United States Court of Appeals
                      For the First Circuit


No. 13-2084

                    UNITED STATES OF AMERICA,

                            Appellee,

                                v.

     XAVIER JIMÉNEZ-BENCEVI, a/k/a Xavi, a/k/a Benjie Rafael
    Alicea-Colón, a/k/a José Andino, a/k/a Reinaldo Jiménez-
           Bencevi, a/k/a Benjamín Amésquita-González,

                      Defendant, Appellant.


          APPEAL FROM THE UNITED STATES DISTRICT COURT
                 FOR THE DISTRICT OF PUERTO RICO

         [Hon. José Antonio Fusté, U.S. District Judge]


                              Before

                 Torruella, Thompson and Kayatta,
                          Circuit Judges.


     John R. Martin, with whom Laura Maldonado-Rodríguez, were on
brief, for appellant.
     Luke V. Cass, Assistant United States Attorney, with whom Rosa
Emilia Rodríguez-Vélez, United States Attorney, Nelson Pérez-Sosa,
Assistant United States Attorney, Chief, Appellate Division, and
John A. Mathews II, Assistant United States Attorney, were on
brief, for appellee.



                           June 3, 2015
          TORRUELLA, Circuit Judge.       Appellant Xavier Jiménez-

Bencevi ("Jiménez") was convicted of tampering with a federal

witness, possession of a firearm in furtherance of a crime of

violence, use of a firearm during and in relation to crimes charged

in the indictment, and use of a cell phone in attempting to commit

kidnapping. Because the acts resulted in the death of the witness,

Delia Sánchez-Sánchez ("Sánchez"), Jiménez faced the death penalty,

though the jury ultimately rejected that punishment and instead

recommended a sentence of life imprisonment without the possibility

of release.

          Jiménez now appeals, complaining that his trial was

fatally flawed in three respects.         First, he argues that the

district court violated his immunity agreement with the government

when it insisted that a defense expert be informed of a proffer

made in an attempt to negotiate a plea.    Second, he claims that the

district court improperly restricted his right to cross-examine two

cooperating witnesses by preventing Jiménez from inquiring into

their exposure to a death-penalty-eligible offense.         Finally,

Jiménez contends that, with respect to the witness tampering

charge, the evidence was insufficient to support his conviction

because the government did not prove beyond a reasonable doubt that

Jiménez murdered Sánchez to prevent her from providing evidence to

federal authorities regarding a federal crime.     Though we find no

merit to Jiménez's second and third claims of error, we agree that


                               -2-
the district court improperly violated the immunity agreement.

Accordingly, for the reasons that follow, we reverse.

                          I.   Background

          On June 21, 2010, Sánchez was shot and killed in broad

daylight in front of the Colmado Hernández mini market in Bayamón,

Puerto Rico.   The entire incident was captured on the market's

security camera.   According to the footage, a car carrying Sánchez

and two others -- later identified as Ronnie Pérez-Albino ("Pérez")

and his mother Gloria Albino-Figueroa ("Albino") -- arrived at the

Colmado Hernández at approximately 2:00 p.m.      Both Sánchez and

Albino exited the vehicle, and almost immediately thereafter a

white Honda Accord arrived.    Two men, neither of whom could be

identified from the video, exited the Honda, grabbed Sánchez, and

attempted to force her inside their car.      Sánchez resisted and

screamed, and a struggle ensued.1     She eventually fell to the

ground, at which point one of the men -- wearing jeans and a black

shirt with a white design -- removed from his waistband a pistol

which appeared to have been modified to fire automatically and shot

Sánchez seven times.   With Sánchez still lying on the ground, the

two men got back into the white Honda and drove away.

          Following an investigation, authorities came to believe

that the shooter was Jiménez, the owner of a drug point at the



1
  While this struggle was occurring, Pérez pulled his mother back
inside his vehicle.

                                -3-
Falín Torrech housing project in Sierra Bayamón and a fugitive who

had posted bond and fled from a pending Puerto Rico murder charge.

His brother Alexis Jiménez ("Alexis") was also Sánchez's boyfriend.

Jiménez was indicted on March 23, 2012, and arrested three days

later.   On January 10, 2013, the grand jury returned the present

superseding indictment.      This four-count indictment charged: (1)

tampering with a witness in violation of 18 U.S.C. § 1512(a)(1)(C)

by killing Sánchez through the use of a firearm with the intent to

prevent her from communicating to a federal law enforcement officer

information related to the commission or the possible commission of

a federal offense; (2) possession of a firearm modified to fire

automatically in furtherance of the crimes charged in Counts One

and   Four    of   the   indictment,    in    violation   of   18   U.S.C.

§ 924(c)(1)(A)(iii) and (B)(ii); (3) using a firearm during and in

relation to the crimes charged in Counts One and Four of the

indictment, in violation of 18 U.S.C. § 924(j); and (4) using a

cell phone in attempting to commit the kidnapping of Sánchez, in

violation of 18 U.S.C. § 1201(a)(1).         The indictment also included

a notice of special findings necessary for the government to seek

the death penalty.

             Approximately one month before the trial's April 15,

2013, start date, Jiménez approached the government regarding the

possibility of entering a guilty plea in exchange for the removal

of the death penalty.      In addition to agreeing to a sentence of


                                  -4-
life without the possibility of release, the government required

Jiménez to provide a proffer containing both a detailed admission

of his guilt to all the crimes he was charged with and any known

information regarding other federal offenders.              The parties also

agreed that the proffer would be covered by direct use immunity.

The agreement provided that

            the United States agrees that no statements
            contained in the written proffer will be used
            against [Jiménez] directly in any criminal
            case in the District of Puerto Rico. However,
            the United States may make derivative use of
            and may pursue any investigative leads
            suggested by any statements or information
            provided, including use in any criminal case
            against [Jiménez]. That is, the United States
            remains free to investigate any leads derived
            from information provided by [Jiménez], and to
            use any evidence gained as a result of such
            investigation in any subsequent prosecution of
            [him]. Further, should [Jiménez] subsequently
            testify in a manner inconsistent with any
            information provided in the written proffer,
            he may and will be cross-examined, confronted
            and impeached by these statements.

After    reviewing   Jiménez's   proffer,       the    government   ultimately

rejected his offer to plead guilty, and the case proceeded to

trial.

            The trial's guilt phase lasted three days, and the

government presented over ten witnesses.2             Carmen Fernández-Ortega

("Tata"),    a   resident   of   the    Falín   Torrech     housing   project,

testified that both her husband and Jiménez's brother Alexis sold



2
    Only the witnesses relevant to this appeal will be discussed.

                                       -5-
crack cocaine and marijuana for Jiménez at the drug point.        She

explained that she and Sánchez were friends and that Sánchez was

vocal about her disapproval of her boyfriend Alexis's involvement

in the drug operation. Indeed, according to Tata, whenever Sánchez

would arrive at the drug point, Jiménez would become upset and a

confrontation would ensue.

          Tata further testified that, as "a joke," she and Sánchez

would record each other's conversations on their cell phones and

that many of those conversations involved Jiménez.     She elaborated

on one conversation in particular, where Sánchez stated that she

would "turn him in to Justice."         Tata's husband overheard this

recording and informed Jiménez.    Jiménez subsequently listened to

the recording himself, became upset, hit Tata in the chest with the

phone, and left, taking the phone with him.

          Pérez and Albino also testified, explaining how and why

they brought Sánchez to the Colmado Hernández mini market the day

she was murdered.   Pérez testified that Jiménez had heard a cell

phone recording of Sánchez in which she stated that she would hand

him over to federal agents, and as a result Jiménez had asked Pérez

to locate Sánchez for him because he wanted to stop her from

talking to the authorities. To accomplish this, Pérez enlisted the

help of his mother, Albino.   According to Albino, Sánchez was her

neighbor and the two had a friendly relationship which often

involved Albino giving Sánchez a ride to the Colmado Hernández mini


                                  -6-
market.    Pérez and Albino exploited this relationship and offered

to drive Sánchez to the Colmado Hernández mini market on June 21,

2010, the day of the murder, so that Sánchez could withdraw money

there.    Pérez explained that once Sánchez accepted their offer, he

informed Jiménez that they would arrive around 2:00 p.m.

            Both Pérez and Albino identified the shooter in the video

as Jiménez. Pérez stated that after the murder, Jiménez called him

and told him that he "wanted to shoot her in the forehead, but that

he had to bring the chip down."          Jiménez added that Pérez needed

"to shut [his] mouth or the same thing would happen to [him]."

Albino corroborated this, testifying that "Xavier took out a pistol

from his waist and shot [Sánchez]."          She added that Jiménez killed

Sánchez "[b]ecause she was going to hand him over to the Feds."

            In addition to these three witnesses, the government

linked    Jiménez   to   the   crime   through   the   following   evidence:

testimony of numerous police, forensic, and cooperating witnesses;

the previously-described surveillance footage outside the Colmado

Hernández mini market; phone records between Jiménez and Pérez;

photographs of Jiménez found in a wallet in the white Honda Accord;

and the combination of video footage at a Kentucky Fried Chicken

showing a man with the same black shirt and white design as the

shooter purchasing food, and a KFC food receipt (found in the Honda

Accord) showing Jiménez contemporaneously purchasing food there.

The government also provided the testimony of Luz Enid Aponte,


                                       -7-
Sánchez's probation officer, who testified that on June 8, 2010, an

FBI task force officer asked her not to visit Sánchez because

Alexis had been stopped and questioned about whether Sánchez was

providing information to the government.3       When Aponte and Sánchez

met approximately one week later as part of Sánchez's probation

requirements, Sánchez confirmed to Aponte that she was cooperating

with the FBI, that Jiménez owned a drug point at Falín Torrech, and

that he had threatened her.

           Jiménez's defense strategy, meanwhile, was to create

reasonable doubt by suggesting that the shooter in the video was

not Jiménez but rather Raymond Jiménez ("Raymond"), Jiménez's

brother and the twin brother of Alexis.            To accomplish this,

Jiménez intended to employ a two-prong approach.       First, he worked

to discredit Pérez and Albino through cross-examination aimed at

establishing that they were either protecting or in fear of the

real shooter.    Jiménez introduced telephone records between Pérez

and two major drug offenders -- José Jiménez-Echevarría ("Lechón")

and   Harold   Ayala-Vásquez   ("Harry")   --   throughout   the   day   of

Sánchez's murder, and Pérez admitted that he never told the agents



3
   Sánchez was indeed providing information to the government.
Officers inspecting Sánchez's body found a piece of paper
containing telephone numbers belonging to federal agents. One of
those numbers belonged to FBI Task Force Investigative Agent Pablo
Irizarry-Ayala ("Irizarry"), who testified that he had met with
Sánchez and she had provided the FBI with information related to
both Jiménez –- who she described as the leader of an organization
in the Falín Torrech housing project in Bayamón -- and Alexis.

                                  -8-
about these calls.     Moreover, Pérez conceded that he gave the

agents several different versions of the events surrounding the

shooting.     Jiménez also elicited testimony to the effect that

Sánchez had bragged that she was going to take everybody down and

that "everybody" included both Lechón, who was in a relationship

with Albino, and Raymond.

            Jiménez next aimed to demonstrate that Pérez and Albino

were biased as a result of the plea and cooperation agreements they

each had signed with the government.   According to the agreements,

Pérez and Albino each agreed to plead guilty to tampering with a

witness and to cooperate with the government against Jiménez, and,

in exchange, the government would recommend a sentence of no more

than seventy months.      When Jiménez's counsel asked Pérez if,

"[w]hen you were arrested for your involvement in this case, a

death eligible Indictment was filed against you?" the government

objected, and a bench conference ensued.   During the sidebar, the

government argued that Pérez was only charged with tampering with

a witness, which was not a death-eligible offense.         Jiménez,

meanwhile, argued that although Pérez and Albino were indicted on

non-death-eligible offenses, the initial complaints filed against

them were certified as potential death-penalty cases, and he had a

right to probe whether the ultimate indictments not charging death-

eligible offenses were the result of a covert agreement with the

government.


                                 -9-
          The   district   court   reviewed   Pérez's   indictment   and

rejected Jiménez's argument, concluding that "[t]his is not a death

penalty eligible case, what he pled to."      It added that Pérez

          pled under 10-452 with tampering with a
          witness.   That's what he was charged with.
          Therefore, it was totally misleading to
          indicate to the jury or try to make the jury
          understand that at one point in time he was a
          death penalty eligible defendant.     He was
          never a death penalty eligible defendant.
          It's as simple as that.

The bench conference then ended, and Jiménez continued with his

cross-examination, exploring other aspects of Pérez's plea and

cooperation agreement, as well as other topics such as Pérez's

involvement with drugs, his destruction of property, and violations

while in federal prison.

          Following the cross-examination, the parties revisited

the death-penalty issue outside the presence of the jury.       During

this exchange, the district court sought more information so it

could determine whether Pérez's and Albino's indictments were

indeed the result of an agreement with the government.               The

government responded that there was no cooperation agreement in

place at the time the indictment was filed and that the reason the

government decided not to indict for a death-eligible offense was

because it lacked any evidence that either Pérez or Albino knew

that Jiménez planned to kill Sánchez at the Colmado Hernández mini

market.   According to the government, it wanted to charge "what

[it] could reasonably prove beyond a reasonable doubt for sure."

                                   -10-
           Still      not   entirely      convinced,       the    district    court

proceeded to question both Pérez's and Albino's defense counsels.

Both   attorneys   confirmed       what    the    government      had   proffered,

explaining to the district court that there was never a deal

trading   cooperation       for    a    non-death-eligible         "wishy    washy"

indictment.    They also emphasized that even before the indictments

were filed, both attorneys were adamant in communications with the

government that neither Pérez nor Albino took Sánchez to the mini

market knowing that she was going to be killed.                  Given all of this

information,    the     district       court     upheld    its    initial    ruling

prohibiting Jiménez from questioning either Pérez or Albino about

exposure to the death penalty. It emphasized, however, that except

for the death-penalty inquiry, Jiménez could ask any question he

wanted on the issue of the plea agreement.                Though Jiménez did not

ask Pérez anything further, he did question Albino about her plea

and cooperation agreement and explored her potential bias due to

her desire for a lower sentence.

           The second prong of Jiménez's defense strategy focused on

the surveillance video.           As noted above, the video showed the

shooter wearing jeans and a black shirt with a white design but did

not capture his face.         Jiménez intended to present the expert

testimony of William J. Stokes, the former Chief of the Special

Photographic Unit of the FBI Laboratory in Washington, D.C., who

would have testified that the person in the surveillance video


                                        -11-
could not have been Jiménez.       Specifically, Stokes would have

testified that after reviewing the surveillance footage and going

to the Colmado Hernández mini market to take measurements, he

concluded that the shooter in the video was at least 5'10½" --

several inches taller than Jiménez, who stood at 5'7".         Jiménez

would have also introduced evidence showing that his brother

Raymond was approximately 5'10".

           The   government   objected   before   trial   to   Stokes's

testimony, based on the proffer Jiménez had made in an attempt to

negotiate a plea.    According to the government, it was unethical

for Jiménez's counsel to present an expert stating that the shooter

was too tall to be Jiménez because the proffer agreement admitted

that Jiménez "was the shooter of Sánchez-Sánchez."        The district

court rejected this argument, but nevertheless opined that Jiménez

did have an obligation to inform Stokes of the information in the

proffer:

           I want you to be clear that I am not telling
           you on the record in case there is an appeal
           or something that I am foreclosing you [from
           calling Stokes]. What I am saying is that if
           there is a proffer, a proffer that clearly
           establishes a point, and that proffer comes to
           -- comes before me in the context of the
           pretrial practice of this case, as it
           happened, I cannot in good conscience allow an
           expert who has not been made aware of the
           proffer to give an expert opinion on something
           where he's missing evidence, he's missing
           facts, because I would then be in a sense part
           and parcel to the giving of evidence that is
           not realistic or true.


                                 -12-
Jiménez objected, arguing that "[i]f that's the fact, then [Stokes]

can be cross-examined about [the proffer], and then it comes in, so

we're stuck."     The district court essentially agreed, stating that

"[i]f it comes out good the way you do it, fine.         If it bounces in

your face, it's a big problem that you have."

            During trial the following day, Jiménez raised the issue

again in an attempt to make a proffer to the court.         The district

court reemphasized its prior point, explaining that "[w]hat you

cannot do is hire an expert, once again, give him selective

information for him to give you an opinion when you know that some

of the facts that he has, that he doesn't have, make his opinion

totally wrong.     You cannot do that."    The court effectively made

clear that the expert could not offer his opinion as it stood to

the jury.    If Jiménez called the expert to do so, the district

court would voir dire him, revealing the substance of the proffer.

Then, reasoned the court, the expert would likely recant. And even

if he did not, the court would not allow Jiménez to "use an expert

to give an imprimatur of expertise on something that [Jiménez]

know[s] is totally false."         As a result, Jiménez never called

Stokes to testify.

            Jiménez was ultimately convicted on all four counts of

the superseding indictment. Following the guilty verdict, the case

proceeded to the sentencing phase to determine whether or not the

death   penalty   would   be   imposed.   After   five   days,   the   jury


                                   -13-
unanimously rejected the death penalty and recommended a sentence

of life without the possibility of release.           The district court

imposed this sentence on August 6, 2013, and this timely appeal

followed.

                            II.    Discussion

            On appeal, Jiménez raises three issues. First, he argues

that the district court violated his immunity agreement with the

government when it insisted that Stokes be informed of admissions

made in Jiménez's proffer, despite the proffer being protected by

direct-use immunity.      Second, Jiménez claims that the district

court improperly restricted his cross-examination of Pérez and

Albino by preventing him from inquiring into their initial exposure

to a death-penalty-eligible offense as a bias and motivation for

their cooperation and testimony.      Finally, Jiménez contends that,

with respect to Count One's witness tampering charge, the evidence

was insufficient to support his conviction because the government

did not prove beyond a reasonable doubt that he murdered Sánchez to

prevent   her   from   providing   evidence     to   federal   authorities

regarding a federal crime.    We address each in turn.

A.   The Immunity Agreement

            We first address Jiménez's argument that the district

court violated his immunity agreement with the government -- made

in a desperate attempt by Jiménez to negotiate a plea and avoid the

death penalty -- when the district court required Jiménez to inform


                                   -14-
Stokes, his photographic and video expert, of the proffer (and thus

Jiménez's admissions) before the expert would be permitted to

testify.   Before we reach the merits, however, we must address a

potential procedural barrier raised by the government: that Jiménez

waived this argument.

           1.   Waiver

           The government contends that because Jiménez never called

Stokes to testify at trial, he waived any objection regarding

Stokes's potential testimony.     In support, it cites to a host of

cases -- from this Circuit and others -- that uniformly hold that

a defendant cannot challenge conditional in limine rulings unless

the witness actually testifies at trial and the conditional ruling

is upheld. See, e.g., United States v. Vázquez-Botet, 

,

50 n.7 (1st Cir. 2008); United States v. Holmquist, 

,

164 (1st Cir. 1994); see also Jones v. Kassulke, No. 95-6459, 

, at *4 (6th Cir. Oct. 23, 1997) (unpublished table

decision); Bedoya v. Coughlin, 

, 352 (2d Cir. 1996);

United States v. Cree, 

, 479 (8th Cir. 1985).

           Vázquez-Botet and Holmquist, however, establish only the

general    proposition   that   when    a   district   court   has   only

conditionally ruled on evidence or testimony, and remains willing

to consider it, a party must offer it if that party wishes to later

complain about its exclusion.      Waiver simply does not apply to

failures to revisit unconditional in limine rulings.       See Crowe v.


                                 -15-
Bolduc, 

, 133 (1st Cir. 2003); 

n.12.

               While the court strongly tipped its hand that it would

insist that the expert be made aware of the proffer, and likely be

exposed to cross-examination on the issue, we agree that, initially

at    least,    some    of   those   remarks   in   and   of   themselves   were

conditional.      However, throughout the exchange, the district court

made its views increasingly definitive. When Jiménez revisited the

issue again at trial, he received reaffirmance of the district

court's decision that the expert must be told of the proffer before

the court would even consider allowing him to testify.              Along with

this requirement came the district court's ultimate conclusion that

the expert would likely recant upon learning of the proffer; and if

he did not, the court would not allow him to testify.4             This ruling

can only be characterized as unconditional, and thus Vázquez-Botet

and    Holmquist       are   inapplicable.      We    therefore    reject    the



4
     The district court stated that

       I offered you to have the witness sit here and be voir
       dired and be asked whether in light of that information,
       he would still be willing to give his testimony. And I
       bet you that he would have said no, because once he gets
       to know the reality of the facts, no serious individual
       is going to take the stand and give the testimony of the
       kind that you want under these circumstances.

It then clarified that while Jiménez's counsel could argue
"whatever [he] want[ed]," he could "not use an expert to give an
imprimatur of expertise on something that [counsel] know[s] is
totally false."

                                       -16-
government's waiver argument and turn to the merits of Jiménez's

objection.

             2.   The District Court's Actions

             "Informal   immunity     agreements,   such   as   proffer

agreements, 'are shaped . . . by the language of the contract

conferring the immunity.'"      United States v. Melvin, 

,

37 (1st Cir. 2013) (alteration in original) (quoting United States

v. Hogan, 

, 388 (1st Cir. 1988)).         Accordingly, the

meaning of the proffer agreement, and whether it was violated, are

reviewed de novo. 

this review, we are primarily

guided by contract-law principles, including the familiar tenets

that contracts should be construed to give effect to every word,

clause, and phrase, and that when a term is ambiguous, it is to be

construed against the drafter -- in this case the government.      

primarily guided, though, because the agreement is made in

the course of a criminal proceeding.          To that end, "[p]roffer

agreements are sui generis, and the contract-law principles that

courts use in construing them are glossed with a concern that the

defendant's consent to appear at a proffer session should not

become a lever that can be used to uproot his right to fundamental

fairness under the Due Process Clause." 

see also United

States v. $87,118.00 in U.S. Currency, 

, 517 (7th Cir.

1996) ("[S]uch agreements are unique contracts and the ordinary

contract principles are supplemented with a concern that the


                                    -17-
bargaining   process   not     violate    the   defendant's   rights    to

fundamental fairness under the Due Process Clause." (internal

quotation marks omitted)). As a result, a violation of an immunity

agreement is a due process violation.       

.

          Rule 410 of the Federal Rules of Evidence and Rule 11(f)

of the Federal Rules of Criminal Procedure set the background rule:

subject to certain non-applicable exceptions, "statements made in

the course of plea negotiations . . . are inadmissible."               This

background   rule,   though,   may   be   waived.    United   States     v.

Mezzanatto, 

, 197, 210 (1995).           Here, the parties

agreed to a waiver that stated as follows:

          So long as [Jiménez] provides complete and
          truthful information in the written proffer,
          he shall have the protection afforded by
          direct use immunity; that is, the United
          States agrees that no statements contained in
          the written proffer will be used against him
          directly in any criminal case in the District
          of Puerto Rico.    However, the United States
          may make derivative use of and may pursue any
          investigative    leads   suggested    by   any
          statements or information provided, including
          use in any criminal case against [Jiménez].
          That is, the United States remains free to
          investigate any leads derived from information
          provided by [Jiménez], and to use any evidence
          gained as a result of such investigation in
          any subsequent prosecution of [Jiménez].
          Further, should [Jiménez] subsequently testify
          in a manner inconsistent with any information
          provided in the written proffer, he may and
          will   be   cross-examined,   confronted   and
          impeached by these statements.

Nothing in this language even remotely granted the government the

right to use the proffered admission in cross-examining Jiménez's

                                  -18-
witnesses.    The omission is especially telling when this agreement

is compared to others used both in this Circuit and throughout the

country which grant the government permission to use the proffer to

rebut contrary evidence elicited from other defense witnesses.

Cf., e.g., 

("No statements made or other

information provided . . . will be used by the United States

Attorney directly against him, except for purposes of cross-

examination and/or impeachment . . . ." (second alteration in

original)); United States v. Chiu, 

, 626 (9th Cir.

1997) ("[T]he government may use . . . statements made by you or

your client at the meeting and all evidence obtained directly or

indirectly    from    those   statements     for     the    purpose       of   cross-

examination should your client testify, or to rebut any evidence,

argument or representation offered by or on behalf of your client

in connection with the trial . . . .").

             It is clear, therefore, that the government could not use

the proffer to cross-examine or otherwise impugn the expert.                        As

the district court itself noted, the proffer language "does not

include   the    possibilit[y]      of    opening     the    door    through        the

presentation     of   evidence.      It    has   to    be    if     the   defendant

testifies."      Yet this is more or less what the district court

itself    did,   treating     the    proposed       expert    testimony        as     a

justification for the court's use of the proffer.                 Indeed, it went

further, first using the proffer to find as a fact that Jiménez was


                                     -19-
the shooter, and then announcing that the expert would either come

to that conclusion when shown the proffer, or not be allowed to

testify.    This is, in no uncertain terms, a violation of Jiménez's

right to due process of law.     See 

.

            The government makes a number of arguments in an attempt

to overcome this obvious violation.         We find none persuasive.

First, it suggests that the district court's order allowing the

proffer to be used against Jiménez was a derivative, not direct,

use   of   the   proffer.   However,   derivative   means   "[s]omething

derived; a thing flowing, proceeding, or originating from another."

United States v. Scott, 

, 304 (D. Mass. 2014)

(alteration in original) (quoting The New Shorter Oxford English

Dictionary 641 (1993)) (internal quotation marks omitted).         Here,

by contrast, the district court would not have used any information

derived or flowing from the proffer after subsequent investigation;

it would have used the proffer itself.     See 

(holding that an officer's voice identification of the defendant,

made after hearing the defendant during a proffer session, was a

direct use of the proffer); United States v. Pielago, 

,

710 (11th Cir. 1998) (explaining direct use immunity to mean that

the government "may not use [the information or statements] as

evidence to obtain an indictment or guilty verdict").

            In this manner, the district court itself treated the

proffer as irrefutably establishing a fact (that Jiménez was the


                                 -20-
shooter) and then used that fact as a basis for precluding the

expert from giving expert testimony that refuted it. As noted, the

district   court   did   not   claim   that   the   proffer   allowed   the

government to use it to knock out Jiménez's expert witness.

Rather, the court asserted its own independent authority as a

"gatekeeper" of expert testimony under Rule 702, to use the proffer

in this manner.     In so proceeding, the district court clearly

erred.

           To begin, we see little advantage and much unfairness in

allowing a district court to use a defendant's proffer against the

defendant in a manner not allowed by the proffer.             If a proffer

allows only uses A and B, but the government can give the proffer

to the court, which then uses it to do C at trial, proffers -- a

valuable tool for both law enforcement and defendants facing severe

sentences -- will be rendered unpredictable in their enforcement,

and thus less likely to be made.         The aim of an agreement not to

use a proffer at trial against a non-testifying defendant is not to

keep the government from using the evidence, it is to keep the

judge and jury from using the evidence.

           Second, the district court was simply wrong to treat the

proffer as establishing a fact, much less the fact of guilt. There

are many possible reasons why a defendant seeking to avoid the

death penalty might conditionally admit to a false fact to see if




                                  -21-
a sentence can be avoided.5       He might so fear death over a long

sentence that a trade-off is seen as reasonable; he might be

protecting another person; he might be of impaired capacity; or he

might be deluded.    A proffer, much less an unaccepted proffer, is

simply not the same thing as a guilty plea or conviction.           Yet, the

district   court   treated   it   as   such   in   order   to   eliminate   an

important defense witness.

           A simplified example highlights the error here.           Imagine

the defense found a high-resolution video of the shooting, clearly

showing that the shooter was someone other than Jiménez, and

Jiménez wanted to use an expert to authenticate the video.             Under

the district court's reasoning, such a piece of evidence would have

been automatically excluded as not "realistic or true" because it

contradicted the statement in the proffer.           This makes no sense.6


5
   In no way are we suggesting that a defendant's proffer and
admission of guilt should be taken with a grain of salt. In the
run-of-the-mill case, it is in a defendant's best interest to tell
the truth, and he or she often has little incentive to lie.
However, as the Supreme Court has stated for over forty years,
"death is different." See, e.g., Ring v. Arizona, 

,
605-06 (2002); Murray v. Carrier, 

, 526 (1986)
(Brennan, J., dissenting); Gregg v. Georgia, 

, 188
(1976).    A defendant facing the death penalty has a strong
incentive to say whatever is needed to eliminate a potential death
sentence and preserve his life.    Indeed, when we asked learned
counsel at oral argument whether he believes defendants sometimes
admit guilt in a proffer in order to avoid a severe sentence even
though they are not guilty, learned counsel unequivocally and
succinctly stated, "Yes."
6
   To the extent one tries to distinguish this example by arguing
that the expert testimony here is less compelling, we note that
such an argument would hinge on a judgment about the persuasiveness

                                   -22-
            Finally, the government argues that it was acceptable for

the district court to require the proffer be disclosed because

allowing Stokes to testify without knowledge of the proffer would

have created an ethical violation since Jiménez's counsel would be

allowing   the    presentation     of    false   testimony.     We   disagree.

Attorneys practicing before the District Court for the District of

Puerto Rico are bound by the American Bar Association's Model Rules

of Professional Conduct.      D.P.R. R. 83E(a).        Rule 3.3(a) of these

Rules requires a lawyer to "not knowingly . . . offer evidence that

the lawyer knows to be false."            Model Rules of Prof'l Conduct R.

3.3(a)(3). The comment to this Rule elaborates that the prohibition

"only applies if the lawyer knows that the evidence is false" and

that a "lawyer's reasonable belief that evidence is false does not

preclude its presentation to the trier of fact."              

            Here, Jiménez's counsel had reason to be skeptical of the

admission and thus did not "know" that Stokes's expert opinion was

false.     First, when Jiménez was initially arrested, he denied

involvement, instead stating that the shooter was his brother

Raymond.    Second, as discussed above, the two eye-witnesses --

Pérez and Albino -- were not the most credible of witnesses: they

provided    the    police   with    changing      stories,    they   withheld

information regarding who they were in contact with the day of



of that testimony -- a judgment which would go well beyond any
gate-keeping role.

                                        -23-
Sánchez's murder, they had relationships with two other likely

suspects, and their testimony was part of a plea and cooperation

agreement.    Third, Stokes -- a former FBI agent with over twenty-

five years experience who was trained in examining photographic and

video evidence -- opined that the shooter was too tall to be

Jiménez.   Fourth, Jiménez was desperate to avoid the death penalty

and the government was adamant that it would not consider any plea

agreement unless Jiménez admitted to all of the charges. Given all

of this, Jiménez's counsel could reasonably conclude that Jiménez's

admission might have been false and that he was simply stating

whatever he had to in order to avoid the death penalty.

             Moreover,   there   is    nothing   to   suggest   that   Stokes

believed his testimony was false.            This is no different than an

alibi witness believing, though possibly mistakenly, that he or she

saw a defendant at one location despite a defendant's proffer to

the contrary.     Under the district court's and the government's

rationale, the alibi witness would be unable to testify.               This is

not what our justice system requires.7           See, e.g., Mich. Op. CI-


7
   We also take issue with the district court's comment that it
"ha[s] an obligation to make certain that the facts that come out
are as truthful as possible to the reality of the case. I cannot
close my eyes to that reality. It would be improper, wrong for me
to do that, and I will not allow that." District courts "close
their eyes" to pertinent evidence all the time. For example, that
is the whole point of motions to suppress; if evidence or
statements are suppressed, courts and parties pretend that the
evidence does not exist. Similarly, if evidence is excluded under
Rule 403 of the Federal Rules of Evidence, pertinent and relevant
evidence is ignored by the court and the parties because of a

                                      -24-
1164 (Jan. 23, 1987) (finding no ethical violation in presenting an

alibi witness who truthfully believes that the defendant was

somewhere else at the time of the offense even though the client

had revealed to counsel that he committed the crime).

            The government points to two district court cases which

contrarily hold that a defense attorney is ethically bound from

presenting evidence which conflicts with statements made during his

client's proffer, even if that proffer is subject to direct-use

immunity.    See United States v. Burnett, Criminal Action No. 08-

201-03, 

, at *5 (E.D. Pa. July 17, 2009) ("Absent a

good-faith basis, within the operation of the Pennsylvania Rules of

Professional     Conduct,    [defendant's]   counsel   may    not    present

evidence    or   arguments   on   [defendant's]   behalf     that   directly

contradict the admissions made by [defendant] during his proffer

sessions."); United States v. Lauersen, No. 98CR1134 (WHP), 

, at *1 (S.D.N.Y. Nov. 13, 2000) ("This Court finds that

[defendant's] waiver of rights is invalid to the extent that the

Government seeks to use her statements for purposes other than to

impeach [defendant] if she were to testify.            However, absent a

good-faith basis, [defendant's] counsel may not present evidence or

arguments on [defendant's] behalf that directly contradict specific


belief that it is unduly prejudicial. This is no different.
Jiménez's proffer, for all intents and purposes, did not exist
unless he testified. Just like excluded evidence, the district
court had an obligation to "close [its] eye to that reality" unless
Jiménez took the stand.

                                    -25-
factual assertions summarized in the Form FD-302 prepared by the

Government.").    Both cases, however, carve out an exception for

evidence presented with a "good-faith basis."     Burnett, 

, at *5;   Lauersen, 

, at *1.   We believe that

the situation presented here, for the reasons discussed above,

would qualify as a "good-faith basis" for presenting Stokes's

expert opinion even though it is contrary to the proffer.     But to

the extent that it would not, we simply note that these cases are

not binding on us, and we believe them to be incorrect.

          3. Harmless Error

          Our conclusion that the breach of the immunity agreement

violated Jiménez's due process rights does not end our discussion.

Instead, we must still determine whether this ruling was harmless.8

To that end, the government must show beyond any reasonable doubt

that the jury's verdict would not have been influenced by the

district court's error.   See 

("Because the

government's adherence to the terms of the proffer agreement is


8
   As we noted in Melvin, "[i]t is open to legitimate question
whether the rule demanding 'automatic reversal' based on 'policy
interest[s]' might apply" to the violation of an immunity

n.3 (second alteration in original)
(quoting Puckett v. United States, 

, 141 & n.3 (2009)).
The Second Circuit, for example, has ruled that it does.        See
United States v. Pelletier, 

, 303 (2d Cir. 1990) ("The
deliberate direct use at trial of all of a defendant's immunized
grand jury testimony in violation of the government's express
agreement to the contrary violates due process and cannot be
considered harmless error." (internal citation omitted)). Like in
Melvin, we decline to answer this question because the error was
not harmless. See 

n.3.

                                -26-
insured by the Due Process Clause, its failure to adhere is

perforce of constitutional dimension.    It follows inexorably that

the   stricter   harmless-error   standard   [of   harmless   beyond   a

reasonable doubt] applies to such a failure.").      This is something

it cannot do.

           As discussed above, the government's evidence consisted

primarily of the following: forensic data linking Jiménez to the

white Honda Accord involved in the shooting; video showing Jiménez

wearing clothing similar to that of the shooter; Tata's testimony

(1) that Sánchez and Jiménez did not get along due to Alexis's

involvement with Jiménez's drug trade and (2) that Jiménez heard a

recording where Sánchez said she was going to report Jiménez to the

Feds; and the testimony and eye-witness identifications by Pérez

and Albino.   With the exception of Pérez's and Albino's testimony,

much of this evidence was circumstantial.

           Of this evidence, by far the most damning was Pérez's and

Albino's testimony that, at Jiménez's request, they took Sánchez to

the Colmado Hernández mini market and then watched as Jiménez

exited the white Honda, tried to abduct Sánchez, and then murdered

her in broad daylight when the abduction failed.      This testimony,

however, was vigorously attacked on cross-examination.         Jiménez

highlighted that both Pérez and Albino were potentially biased and

provided multiple reasons for this bias, including strong personal

relationships with others who may have wanted Sánchez dead, fear


                                  -27-
for their safety should they implicate the true shooter, and the

cooperation agreements made with the government to ensure more

lenient sentences.

               Though   the   jury   ultimately    found   Pérez     and   Albino

credible enough to convict Jiménez, we cannot say beyond all

reasonable doubt that the jury would have continued to credit this

testimony and would have come to the same guilty verdict had

Jiménez been able to provide expert testimony -- from the former

Chief of the Special Photographic Unit of the FBI Laboratory, no

less -- concluding that the shooter in the video was too tall to be

Jiménez.       The jury may very likely still have convicted Jiménez,

but it may not have.           Accordingly, the error was not harmless

beyond     a    reasonable    doubt,   and    we   must    reverse    Jiménez's

conviction.

B.   Restrictions on Cross Examination

               Though we are already reversing Jiménez's conviction, we

will still address his Confrontation Clause argument because it has

been fully briefed and will almost certainly arise again should

Jiménez be retried. See Compagnie Nationale Air France v. Castano,

, 208 (1st Cir. 1966) ("Since there must be a new

trial, and this matter is likely to come up again, we will deal

with it.").      According to Jiménez, the district court violated his

Sixth Amendment right to confrontation by forbidding any cross-




                                       -28-
examination about Pérez's or Albino's initial exposure to the death

penalty.   We disagree.

           The Sixth Amendment's Confrontation Clause "guarantees

criminal defendants the right to cross-examine those who testify

against them."    United States v. Vega Molina, 

, 522

(1st Cir. 2005) (citing Davis v. Alaska, 

, 315 (1974)).

It extends to cross-examination "reasonably necessary to delineate

and present the defendant's theory of defense," 

"the right to cross-examine the government's witness about his bias

against the defendant and his motive for testifying," United States

v. Ofray-Campos, 

, 36 (1st Cir. 2008).    Indeed, we have

consistently held that "cross-examination is the principal means by

which the believability of a witness and the truth of his testimony

are tested."     Brown v. Powell, 

, 3 (1st Cir. 1992)

(quoting Kentucky v. Stincer, 

, 736 (1987)) (internal

quotation marks omitted).

           This right, however, has limits, and "[t]he Confrontation

Clause does not give a defendant the right to cross-examine on

every conceivable theory of bias."      United States v. Martínez-

Vives, 

, 53 (1st Cir. 2007) (alteration in original)

(quoting United States v. Callipari, 

, 38-39 (1st Cir.

2004), vacated on other grounds, 

(2005))(internal

quotation marks omitted).     As the Supreme Court explained in

Delaware v. Van Arsdall, 

, 679 (1986),


                                -29-
            [i]t does not follow, of course, that the
            Confrontation Clause of the Sixth Amendment
            prevents a trial judge from imposing any
            limits on defense counsel's inquiry into the
            potential bias of a prosecution witness. On
            the contrary, trial judges retain wide
            latitude insofar as the Confrontation Clause
            is concerned to impose reasonable limits on
            such cross-examination based on concerns
            about,   among   other  things,   harassment,
            prejudice, confusion of the      issues, the
            witness' safety, or interrogation that is
            repetitive or only marginally relevant.


            To that end, our review of a district court's decision to

limit cross-examination involves a two-step inquiry.                   First, we

"review de novo the district court's conclusion that, even though

cross-examination      was   limited,        the   defendant     was     afforded

sufficient leeway to establish a reasonably complete picture of the

witness'   veracity,    bias,   and    motivation."        United      States    v.

Capozzi, 

, 723 (1st Cir. 2007) (quoting United States

v. Byrne, 

, 21 (1st Cir. 2006)) (internal quotation

marks   omitted).       Then,   assuming       this   initial    threshold       is

satisfied, we "review the particular limitations only for abuse of

discretion."     

.

            Here we have little doubt that Jiménez was able to paint

for the jury a complete picture of both Pérez and Albino such that

he "was afforded a reasonable opportunity to impeach" them.                     

marks omitted).                Regarding Pérez, Jiménez

introduced a number of facts calling both his identification of

Jiménez    and   his   credibility    into     question.        First,   Jiménez

                                      -30-
established that beginning the morning of June 21, 2010, and

continuing until after Sánchez's murder that afternoon, Pérez had

multiple conversations with Lechón and Harry -- both of whom were

involved in drug dealing in Falín Torrech and both of whom were

included in Sánchez's threat to take everybody down -- yet failed

to reveal this information to the authorities.               Second, Jiménez

elicited   the    fact   that   Pérez    provided     the   authorities   with

inconsistent versions of his story.         As to Albino, Jiménez showed

a motive for implicating him and protecting Lechón, who he alleged

was potentially the true shooter: Albino was in a relationship with

Lechón.

           Moreover,      though   the     district     court   forbade    any

questioning about death-penalty exposure, it never prohibited

Jiménez from discussing the plea and cooperation agreement itself.

To the contrary, Jiménez cross-examined both Pérez and Albino about

the details of the agreement and their understanding that they

would receive a more-lenient sentence if they cooperated.                 That

Jiménez could not emphasize just how severe Pérez's and Albino's

possible sentences could have been had they not cooperated did

nothing to detract from his central argument: both Pérez and Albino

were   biased    and   motivated   to   provide   incriminating    testimony

against Jiménez in an attempt to look out for their own best

interests and receive a lighter sentence.               We have previously

upheld a district court's decision to prohibit cross-examination


                                    -31-
into a cooperating witness's exposure to the death penalty so long

as the defendant could still probe into other aspects of the plea

agreement, and we see no reason to deviate from that position here.

See 

("[T]he district court did not commit

constitutional error when it declined to allow [defendant] to

inquire into the subject of [the cooperating witness's] avoidance

of the potential death penalty attached to this uncharged crime

which [the witness] had supposedly avoided by cooperating with the

government" because defendant "had considerable ammunition . . .

from which to demonstrate that [the witness] had a powerful motive

to testify in a manner supportive of the government.").

           Reviewing the cross-examinations as a whole, we conclude

that   Jiménez   provided    a    "reasonably   complete   picture   of   the

witness[es]' veracity, bias, and motivation" despite the district

court's limitation, and therefore the limitation did not violate

the Confrontation Clause.         See 

(finding   no    violation   of   the   Confrontation   Clause   where    the

district court prevented the jury from hearing the potential

penalty of life imprisonment that a cooperating witness avoided by

pleading guilty because the jury "was clearly given sufficient

information from which it could conclude that the [accomplice] had

a substantial motivation to testify against petitioner," such as

the specifics of the accomplice's plea agreement, the witness's

criminal record, that the witness had given the police a different


                                     -32-
statement than his testimony, that the witness had stolen the

murder weapon, and that the witness had reviewed the investigative

file before testifying); United States v. Twomey, 

,

1139-40 (1st Cir. 1986) (restricting cross-examination into an

unsubstantiated charge that the witness was involved in two murders

in part because "the circumstances from which the jury could decide

whether [the witness] might have been inclined to testify falsely

in favor of the government was adequately presented"); cf. Vega

(finding a Sixth Amendment violation

where the district court precluded any cross-examination into a

cooperating   witnesses's   motive   for   enlisting   in   the   robbery

scheme).

           Having found that Jiménez's opportunity to impeach Pérez

and Albino satisfied this initial threshold, we turn to whether the

district court nevertheless abused its discretion in precluding

this line of questioning.     "An abuse of discretion has occurred

only if the jury is left without 'sufficient information concerning

formative events to make a discriminating appraisal of a witness's

motives and bias.'"   

(quoting Harris v.

United States, 

, 636 (1st Cir. 1966)) (internal

quotation marks omitted); see also 

("'To establish that the district court has abused its discretion,

the defendant must show that the limitations imposed were clearly

prejudicial.'" (quoting United States v. Williams, 

,


                                -33-
639 (1st Cir. 1993))).         In other words, the restrictions must be

"manifestly unreasonable or overbroad."           

(citation and internal quotation marks omitted).

             Here,    the   district    court's   limitation    was   neither

unreasonable nor overbroad.        We have already explained how Jiménez

questioned Pérez and Albino about the details of their plea and

cooperation agreements and about their other potential biases and

motivations for testifying.            Moreover, as the district court

correctly    noted,    while   a   complaint   alleging    a   death-eligible

offense was initially filed, Pérez and Albino were never indicted

on this charge and consequently were never actually exposed to the

death penalty.       Still, when Jiménez argued that this was precisely

because of an agreement, the district court inquired further and

questioned the government and both witnesses' attorneys.                Each

party   provided      the   same   information:    the    non-death-eligible

indictment was not a result of an agreement among the parties but

rather due to the lack of evidence that either Pérez or Albino knew

Sánchez would be killed at the Colmado Hernández mini market.            The

district court accepted this explanation and, as a result, believed

that raising the issue with the jury would be misleading and

confusing.

             Given the district court's "wide latitude insofar as the

Confrontation Clause is concerned to impose reasonable limits" on

cross-examination, Van 

, this conclusion


                                       -34-
was not "manifestly unreasonable."    Nor did it prejudice Jiménez.

See 

. Accordingly, we find no abuse of

discretion by the district court in prohibiting Jiménez from

inquiring into the witnesses' potential exposure to the death

penalty.   See 

("Nor did the court's

decision to bar the questioning constitute an abuse of its general

discretion. . . .    Any risk that [the witness] would have been

charged with the death penalty offense was at best . . . wholly

speculative."); United States v. Álvarez, 

, 82 (1st Cir.

1993) (finding no abuse of discretion where the district court

prevented the jury from learning of the exact penalties the witness

would face if found guilty); 

(finding

no abuse of discretion where the district court restricted cross-

examination into a witness's supposed involvement in two murders to

establish bias in part because "[t]here is no evidence to support

such a charge, and, in fact, [the witness's] plea agreement

explicitly states that it does not protect him from prosecution for

crimes of violence").

C.   Sufficiency of the Evidence for Count One

           Finally, we must still address Jiménez's sufficiency

argument for double jeopardy purposes.     See Marshall v. Bristol

Superior Court, 

, 18 (1st Cir. 2014) ("It is black

letter law that 'the Double Jeopardy Clause precludes a second

trial once the reviewing court has found the evidence legally


                               -35-
insufficient.'" (quoting Burks v. United States, 

, 18

(1978))). According to Jiménez, there was insufficient evidence to

support his conviction on Count One, the witness tampering charge,

and thus his Rule 29 motion for judgment of acquittal of Count One

should have been granted.          We review this allegation de novo.

United States v. Pérez-Meléndez, 

, 40 (1st Cir. 2010).

In doing so,

            we examine the evidence, both direct and
            circumstantial, in the light most favorable to
            the jury's verdict.     We do not assess the
            credibility of a witness, as that is a role
            reserved for the jury.       Nor need we be
            convinced that the government succeeded in
            eliminating every possible theory consistent
            with the defendant's innocence.     Rather, we
            must decide whether that evidence, including
            all plausible inferences drawn therefrom,
            would allow a rational factfinder to conclude
            beyond a reasonable doubt that the defendant
            committed the charged crime.

States v. Troy, 

, 24 (1st Cir.

2009)) (internal quotation marks and emphasis omitted); see also

United States v. Sepúlveda, 

, 1173 (1st Cir. 1993).

This   is   a    "formidable"    standard   of    review,    so   "defendants

challenging convictions for insufficiency of the evidence face an

uphill battle on appeal."        

(quoting

United States v. Lipscomb, 

, 40 (1st Cir. 2008))

(internal quotation marks omitted).

            In    order   to    establish   a    violation   of   18   U.S.C.

§ 1512(a)(1)(C), the government must prove beyond a reasonable


                                     -36-
doubt    that    there   was    "(1)     a    killing      or   attempted   killing,

(2) committed with a particular intent, namely an intent (a) to

'prevent' a 'communication' (b) about 'the commission or possible

commission of a Federal offense' (c) to a federal 'law enforcement

officer or judge.'" Fowler v. United States, 

, 2049

(2011) (quoting 18 U.S.C. § 1512(a)(1)(C)). Here, Jiménez concedes

that the government satisfied its burden for most of these elements

and only challenges the proof for the element that Sánchez was

killed    in    order    to    prevent       her    from   providing    information

concerning "the commission or the possible commission of a Federal

offense."       According to Jiménez, the evidence showed that if he

killed Sánchez, it was done to prevent her from communicating his

whereabouts to federal officials so that he could be arrested on

the outstanding Puerto Rico murder charge for which he was a

fugitive.       In support of this contention, Jiménez points to the

investigative notes which reported that Sánchez was "willing to

provide [Jiménez's] location to the feds to have him arrested on an

outstanding state warrant."

               While we agree that a jury could have come to this

conclusion, we "need not conclude that only a guilty verdict

appropriately could be reached" in order to sustain the conviction.

(emphasis added).                    To the contrary, "it

is enough that the finding of guilt draws its essence from a

plausible reading of the record."                  Id.; see also Pérez-Meléndez,


                                         

("Nor need we be convinced that the government

succeeded in eliminating every possible theory consistent with the

defendant's innocence." (quoting 

) (internal

quotation marks omitted)). And a review of the record satisfies us

that the government has met its burden.

             At trial, Tata testified that Sánchez was unhappy that

Alexis -- her boyfriend and Jiménez's brother -- was involved in

Jiménez's drug operation. As a result, she and Jiménez did not get

along, and whenever she would arrive at the drug point, Jiménez

would become upset and a confrontation would ensue.                   Tata further

testified that she recorded Sánchez saying that Sánchez would "turn

[Jiménez] in to Justice."             Given that their rocky relationship

stemmed from Jiménez's drug activities and not his status as a

fugitive, the jury could have plausibly inferred that Jiménez

understood    Sánchez      to   be   referring     to   his    drug    trafficking

activities, which is clearly a federal offense.                   See, e.g., 21

U.S.C. §§ 841(a)(1) and 846 (criminalizing possession of controlled

substances with the intent to distribute and conspiracy to possess

controlled substances with the intent to distribute, respectively).

             The   government        presented    additional     circumstantial

evidence supporting this inference.              First, Aponte testified that

on June 8, 2010, an FBI task force officer had asked her not to

visit Sánchez because Alexis had been stopped and questioned about

whether   Sánchez    was    providing     information     to    the    government.


                                        -38-
Aponte added that Sánchez later confirmed that she was cooperating

with the FBI, that Jiménez owned a drug point at Falín Torrech, and

that he had threatened her.        Officer Irizarry similarly testified

that Sánchez had provided him with information regarding Jiménez's

drug operations.9         Pérez, meanwhile, testified that Sánchez had

bragged that she was going to take everybody down. It is plausible

to infer that both Alexis and Pérez would have reported these

incidents to Jiménez, and that Jiménez would have interpreted both

the questioning of Alexis and the use of "everybody" to refer to

the drug activity to which multiple people were involved, and not

to Jiménez's status as a fugitive.

              Taking all of this evidence together and making plausible

inferences in the light most favorable to the jury's verdict, we

believe   a    rational    factfinder   could   have   concluded   beyond   a

reasonable doubt that Jiménez intended to prevent Sánchez from

providing information to federal authorities regarding Jiménez's




9
    In his recitation of the facts, Jiménez suggests that the
government violated both 18 U.S.C. § 3432 and Rule 26.2 of the
Federal Rules of Criminal Procedure when it called Officer Irizarry
to testify in support of this element. Jiménez provides no legal
arguments or citations to support this claim, however, so it is
therefore waived. See United States v. Zannino, 

, 17
(1st Cir. 1990) ("[It is a] settled appellate rule that issues
adverted to in a perfunctory manner, unaccompanied by some effort
at developed argumentation, are deemed waived. It is not enough
merely to mention a possible argument in the most skeletal way,
leaving the court to do counsel's work, create the ossature for the
argument, and put flesh on its bones." (internal citations
omitted)).

                                    -39-
narcotics operation -- a federal offense. Accordingly, his Rule 29

motion was properly denied.

                                III. Conclusion

             To    summarize,    the   district     court's   order   requiring

Jiménez's expert witness, Stokes, to be informed of admissions made

by Jiménez in his proffer statement contravened the immunity

agreement, and thus violated Jiménez's due process rights.                This

error was not harmless beyond a reasonable doubt, and therefore

Jiménez's conviction cannot stand.            Should Jiménez be retried, it

will be well within the district court's discretion to limit the

cross-examinations of Pérez and Albino to prohibit any references

to their potential exposure to the death penalty, so long as

Jiménez   is      given   the   same   sufficient    leeway   to   establish   a

reasonably complete picture of both Pérez's and Albino's veracity

as he was during this trial.           Finally, even though the conviction

is reversed due to the violation of the immunity agreement, we

conclude for double jeopardy purposes that there was sufficient

evidence for the jury to have found that Jiménez killed Sánchez in

order   to   prevent      her   from   providing    information    to   federal

authorities concerning "the commission or the possible commission

of a Federal offense," and thus his Rule 29 motion for judgment of

acquittal as to Count One -- the witness tampering charge -- was

properly denied.

             REVERSED.


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