FILED
                                                           United States Court of Appeals
                                 PUBLISH                           Tenth Circuit

                UNITED STATES COURT OF APPEALS January 27, 2020
                                                              Christopher M. Wolpert
                       FOR THE TENTH CIRCUIT                      Clerk of Court
                       _________________________________

UNITED STATES OF AMERICA,

       Plaintiff - Appellee,

v.                                                    No. 18-2182

BRIAN TONY,

       Defendant - Appellant.
                     _________________________________

      APPEAL FROM THE UNITED STATES DISTRICT COURT
             FOR THE DISTRICT OF NEW MEXICO
                ( D.C. No. 1:16-CR-02904-MV-1 )
                _________________________________

Josh Lee, Assistant Federal Public Defender (Virginia L. Grady, Federal
Public Defender, with him on the briefs), Denver, Colorado, for Defendant-
Appellant.

Joseph M. Spindle, Assistant United States Attorney (John C. Anderson,
United States Attorney, and Dustin C. Segovia, Assistant United States
Attorney, Las Cruces, New Mexico, on the brief), Albuquerque, New
Mexico, for Plaintiff-Appellee.
                     _________________________________

Before BRISCOE, KELLY, and BACHARACH, Circuit Judges.
                 _________________________________

BACHARACH, Circuit Judge.
               _________________________________


     This appeal is brought by Mr. Brian Tony, who was convicted of

first-degree murder for fatally stabbing Mr. Pat Garcia during a fight.
Before trial, Mr. Tony sought to introduce evidence that Mr. Garcia had

used methamphetamine before the fight. The district court excluded the

evidence, and Mr. Tony argues that the evidence should have been allowed

into evidence. In our view, the district court excluded the evidence for a

reason unsupported by the record. We thus reverse and remand for a new

trial. 1

I.         The district court excluded the methamphetamine evidence on the
           ground that Mr. Tony failed to identify a proper purpose.

           Mr. Tony admitted that he had killed Mr. Garcia. But Mr. Tony

denied premeditation and asserted self-defense, arguing that he was

protecting himself from Mr. Garcia. Given the assertion of self-defense,

the district court allowed Mr. Tony to present evidence of Mr. Garcia’s

erratic and violent behavior. But Mr. Tony wanted to go further: he wanted

to elicit evidence that Mr. Garcia had reacted erratically and violently

because he was under the influence of methamphetamine. The district court

excluded this evidence under Federal Rule of Evidence 404(b) on the

ground that Mr. Tony had failed to identif y a proper purpose.




1
      Mr. Tony also argues that the judge erred by informing the venire
(upon inquiry) that the case was not a death-penalty case. Given our
reversal based on exclusion of the methamphetamine evidence, we need not
reach Mr. Tony’s argument involving the statement to the venire.

                                         2
II.    Under the abuse-of-discretion standard, reversal is necessary
       when the district court relies on a clearly erroneous
       understanding of the record.

       We review the exclusion of evidence under the abuse-of-discretion

standard. United States v. Ramone, 

, 1234 (10th Cir. 2000).

A court abuses its discretion when relying on a clearly erroneous

understanding of the record. See Cooter & Gell v. Hartmarx Corp., 

, 405 (1990) (“A district court would necessarily abuse its

discretion if it based its ruling on . . . a clearly erroneous assessment of the

evidence.”).

III.   The district court abused its discretion by excluding the
       methamphetamine evidence based on Mr. Tony’s alleged failure
       to identify a proper purpose.

       Rule 404(b) prohibits using evidence of other acts “to prove a

person’s character in order to show that on a particular occasion the person

acted in accordance with the character.” Fed. R. Evid. 404(b)(1). But the

rule provides an exception: evidence of other acts may be admitted for

non-propensity purposes. Fed. R. Evid. 404(b)(2).

       To invoke this exception, the proponent of the evidence bears a

threshold obligation to tell the court what the purpose is. United States v.

Birch, 

, 1093 (10th Cir. 1994). But even if the proponent

identifies a permissible purpose, the evidence may still be inadmissible on

grounds of relevance, unfair prejudice, or necessity of expert testimony.

See Fed. R. Evid. 104(b), 402, 403.

                                       3
      The district court excluded the methamphetamine evidence at the

threshold stage, ruling that Mr. Tony had identified no proper purpose for

the evidence. 2 But this ruling is clearly erroneous based on the record. In

responding to the motion in limine, Mr. Tony stated in writing and in court

that he was offering the methamphetamine evidence to show why Mr.

Garcia was acting erratically and violently. This purpose would have been

permissible under Rule 404(b).

      In responding to the government’s motion in limine to exclude the

methamphetamine evidence, Mr. Tony argued:

            When viewed through a neutral lens, the very evidence
      produced by the Government suggests the victim was the first
      aggressor in this case. The evidence will support that the alleged
      victim was intoxicated on methamphetamine and from the
      electrolytes in his system, that he had been under the influence
      of methamphetamine at the time of the incident. The Defense
      will    introduce    evidence     regarding   the    effects    of
      methamphetamine on human behavior. Such evidence will not be
      offered for the purpose of proving the alleged victim acted in
      conformity with his violent character; rather, pursuant to Rule
      404(b), it will be offered for another purpose. There is no
      question that the alleged victim was not only habitually armed


2
      Mr. Tony also argues that the evidence should have been allowed as
intrinsic evidence. The government argues that Mr. Tony waived this
argument in district court by relying on Rule 404(b). We need not decide
whether Mr. Tony waived the argument. Even if he hadn’t, he would have
forfeited the argument by failing to raise it in district court. United States
v. Tapaha, 

, 909 n.6 (10th Cir. 2018). When an argument is
forfeited, we ordinarily apply plain-error review. United States v. Battles,

, 445 n.9 (10th Cir. 2014). But Mr. Tony does not argue plain
error in this appeal, so we would decline to consider this issue even if it
had not otherwise been waived. United States v. Lamirand, 

,
1098–100 n.7 (10th Cir. 2012).
                                      4
      with a large sheath knife, he used that very knife to inflict a
      potentially mortal wound on the Defendant.

R. vol. I, at 49–50. The government apparently understood this explanation

of the purpose, responding that “the probative value of [Mr. Garcia’s] drug

use to support his ‘violent behavior’ [was] tenuous at best and highly

prejudicial.” 

      The district court then considered the issue at a pretrial hearing.

Moments before discussing the motion in limine, the parties addressed the

need for a jury instruction on self-defense. Urging an instruction on self-

defense, Mr. Tony argued that the jury could reasonably find self-defense

based on his efforts to ward off Mr. Garcia’s methamphetamine-fueled

attack:

            Your Honor, the – I’d ask the Court to take judicial notice
      that meth is one of those drugs that makes people do irrational
      and sometimes highly violent things. Your Honor, we – there
      will be testimony that the deceased kept – kept fighting with Mr.
      Tony continually, and Mr. – the deceased was still alive when
      Mr. Tony finally was able to haul himself out of the arroyo after
      suffering some rather horrible wounds himself. Your Honor, the
      fact that the deceased did have numerous wounds is simply an
      indication how violent the fight itself was, how life-threatening
      it was to Mr. Tony, also.

Suppl. R. vol. IV, at 15. The government again understood the purpose,

acknowledging that Mr. Tony was offering the methamphetamine evidence

to argue that the victim had acted violently: “What Defense is basically

trying to say is somebody who uses methamphetamine is inherently

violent.” 

                                      5
      The court didn’t immediately decide whether it would instruct on

self-defense. The court instead shifted the discussion to the admissibility

of the methamphetamine evidence. With this shift in the discussion, Mr.

Tony did not repeat the purpose offered in his written objection. There was

no need because Mr. Tony had identified this purpose only moments earlier

when arguing that the jury could reasonably find self-defense.

      Given the clarity of Mr. Tony’s explanation and the government’s

understanding, the district court relied on a clearly erroneous view of the

record when ruling that Mr. Tony had failed to identif y a permissible

purpose for the methamphetamine evidence.

IV.   We cannot affirm on alternative grounds.

      This is not to say that the methamphetamine evidence was

admissible, for not all evidence of a witness’s prior drug use is admissible.

Though Mr. Tony identified a proper purpose for the methamphetamine

evidence, it might have been excludable as irrelevant or lacking a

foundation in expert testimony. 3 Fed. R. Evid. 104(b), 402.

      If the evidence were inadmissible on any of these grounds, we might

be able to affirm on alternative grounds. But the district court had


3
      The evidence might have also been excluded under Rule 403, which
requires balancing the evidence’s probative value against dangers such as
the risk of unfair prejudice. Fed. R. Evid. 403. But when a district court
excludes evidence for reasons other than Rule 403, we may not conduct the
balancing test for the first time on appeal. Sprint/United States Mgmt. Co.
v. Mendelsohn, 

, 386–87 (2008).
                                      6
discretion to decide whether the evidence was relevant or required expert

testimony, and the court never exercised that discretion. So we can affirm

on alternative grounds only if it would have been an abuse of discretion to

permit introduction of the evidence. See Ashby v. McKenna, 

,

1151 (10th Cir. 2003) (“[W]ith respect to a matter committed to the district

court’s discretion, we cannot invoke an alternative basis to affirm unless

we can say as a matter of law that ‘it would have been an abuse of

discretion for the trial court to rule otherwise.’” (quoting Orner v. Shalala,

, 1310 (10th Cir. 1994))).

      Under this standard, we consider whether the district court had

discretion to consider the methamphetamine evidence relevant without a

foundation of expert testimony. The government argues that expert witness

testimony was necessary to show that

      •     Mr. Garcia had been under the influence of methamphetamine
            during the fight and

      •     methamphetamine had caused his aggressive behavior.

The district court had discretion to credit these arguments, but the court

also had discretion to reject them.

      The necessity of expert testimony involves the principle of

conditional relevance. Under this principle, a district court may exclude

evidence if the jury could not reasonably find the existence of a

preliminary fact essential to make the evidence relevant. United States v.


                                       7
Platero, 

, 814 (10th Cir. 1995). Though Mr. Tony had agreed

not to present expert testimony, he might not have needed an expert

witness for a reasonable jury to find that Mr. Garcia had been under the

influence of methamphetamine. Methamphetamine had been found on Mr.

Garcia’s body and in his bloodstream. Together, this evidence supported an

inference that Mr. Garcia was on methamphetamine, and lay witnesses may

have been able to testif y that he was high. So Mr. Tony might not have

needed expert testimony to show that methamphetamine causes erratic,

violent behavior. See United States v. Foote, 

, 665 (8th Cir.

1990) (“[T]he effects of cocaine addiction on an individual’s mental

prowess were within the jury’s common understanding.”).

     The district court ultimately had discretion to either (1) decline to

exclude the evidence before hearing whether a lay witness would have

testified that Mr. Garcia was under the influence of methamphetamine or

(2) allow a lay witness to testif y about the effect of methamphetamine on

Mr. Garcia’s behavior. Given this discretion, we cannot affirm on the

government’s alternative grounds. We thus conclude that the district court

abused its discretion in excluding the evidence based on a clearly

erroneous understanding that Mr. Tony had failed to identif y a permissible

purpose.




                                     8
V.    The district court’s error was not harmless.

      Like other errors, abuses of discretion may be harmless. See United

States v. Vaughn, 

, 1051 (10th Cir. 2004) (“[W]e review [the

defendant’s] evidentiary claims for an abuse of discretion, and if we find

an abuse of discretion, we must determine whether the error was

harmless.”). But premature exclusion of the methamphetamine evidence

was not harmless.

      The government bears the burden of showing by a preponderance of

the evidence that the error was harmless. 

error would be harmless

only if it did not substantially affect Mr. Tony’s rights. See United States

v. Glover, 

, 1210 (10th Cir. 2005) (“In non-constitutional

harmless error cases, the government bears the burden of demonstrating, by




4
      In some published cases, we have said that criminal defendants
asserting error bear the burden of proving an effect on their substantial
rights. United States v. Anaya, 

, 448–49 (10th Cir. 1997);
United States v. Mitchell, 

, 1532 (10th Cir. 1997); United
States v. Messner, 

, 1453 (10th Cir. 1997); United States v.
Arutunoff, 

, 1118 (10th Cir. 1993). But both before and after
these cases, we have held that the government bears the burden of showing
harmlessness. See, e.g., United States v. Rivera, 

, 1469 n.4
(10th Cir. 1990) (“[T]he government ordinarily has the burden of proving
that a non-constitutional error was harmless.”); United States v. Harrison,

, 764 (10th Cir. 2014) (“In non-constitutional harmless error
cases, the government bears the burden of demonstrating . . . that the
substantial rights of the defendant were not affected.” (quoting United
States v. Keck, 

, 798 (10th Cir. 2011))).

                                      9
a preponderance of the evidence, that the substantial rights of the

defendant were not affected.”).

      At trial, Mr. Tony denied premeditation and asserted self-defense.

The government focuses on the assertion of self-defense, arguing that the

error was harmless because Mr. Tony could still urge self-defense based on

Mr. Garcia’s erratic and violent behavior. But the government does not

address how the methamphetamine evidence might have affected Mr.

Tony’s denial of premeditation. Without any argument on premeditation,

the government failed to satisf y its burden on harmlessness. We thus must

reverse and remand for further proceedings.

VI.   The appropriate remedy is vacatur of the conviction, not remand
      for consideration of the government’s pretrial argument for
      exclusion under Rule 403.

      Given our need to reverse, we must decide the scope of the remand. 5

Before trial, the government argued in a motion in limine that the

methamphetamine evidence was inadmissible under both Rule 404(b) and

Rule 403. Given the exclusion under Rule 404(b), the court never decided

whether to grant the motion in limine under Rule 403.


5
      In his opening brief, Mr. Tony asked twice for a new trial based on
the erroneous exclusion of methamphetamine evidence. Appellant’s
Opening Br. at 3, 39. In one place, Mr. Tony asked us to remand for the
district court to consider the government’s argument under Rule 403. In a
supplemental letter, Mr. Tony reiterated that he is seeking a new trial
(based on the evidentiary error) rather than a remand for consideration of
the issue under Rule 403.

                                     10
      The government timely objected under Rule 403 and ordinarily would

be entitled to a ruling on this objection. But the government prevailed on

its other objection, obtaining exclusion of the methamphetamine evidence

under Rule 404(b). Given this ruling, we must consider whether to

      •     remand for the district court to decide the admissibility of the
            methamphetamine evidence under Rule 403 or

      •     vacate the conviction and remand for a new trial.

Remanding for the district court to consider the motion in limine would be

troublesome for two reasons.

      First, the trial took place over two years ago. Deciding the Rule 403

issue now would require the district court to travel back in time and

speculate how it would have ruled over two years ago, before hearing the

trial evidence.

      Second, remanding for consideration of the motion in limine would

create a dilemma for the district court, which would have an overwhelming

temptation to rationalize the exclusion of the methamphetamine evidence

under Rule 403. See Dodge v. Cotter Corp., 

, 1229 (10th Cir.

2003) (“We decline to entertain the possibility of a remand to the district

court to make specific findings relative to these experts, for we think no

district court would be well positioned to make valid findings given the

overwhelming temptation to engage in post hoc rationalization of admitting

the experts.”).


                                     11
     For both reasons, we conclude that the appropriate remedy is vacatur

of the murder conviction rather than remand to consider whether to grant

the motion in limine based on Rule 403. See Ruiz-Troche v. Pepsi Cola of

Puerto Rico Bottling Co., 

, 88 (1st Cir. 1998) (deciding that

“the fairest course,” when evidence of the victim’s cocaine use was

improperly excluded, was to order a new trial rather than remand for

consideration of other evidentiary objections); see also Estate of Barabin

v. AstenJohnson, Inc., 

, 465–66 (9th Cir. 2014) (en banc)

(stating that the Court of Appeals would remand for a new trial when the

district court erroneously excluded evidence even if the district court had

failed to address a threshold requirement of admissibility).

     We thus reverse with instructions to vacate the conviction on first-

degree murder and to conduct a new trial on this charge.




                                     12