In the
 United States Court of Appeals
              For the Seventh Circuit
                         ____________

No. 06-2180
UNITED STATES OF AMERICA,
                                               Plaintiff-Appellee,
                                v.

FELIX VASQUEZ-RUIZ,
                                           Defendant-Appellant.
                         ____________
           Appeal from the United States District Court
      for the Northern District of Illinois, Eastern Division.
         No. 00 CR 1044—Matthew F. Kennelly, Judge.
                         ____________
ARGUED JANUARY 12, 2007—DECIDED SEPTEMBER 17, 2007
                    ____________


 Before POSNER, WOOD, and SYKES, Circuit Judges.
   WOOD, Circuit Judge. Felix Vasquez-Ruiz ostensibly
practiced medicine in the Chicago area. In reality, he
was bilking insurance companies by ordering a multitude
of unnecessary tests for patients who visited his clinic.
Eventually he was caught and tried on multiple counts
of mail and healthcare fraud. Nine days into his trial,
however, the proceedings took an unexpected and unset-
tling turn when a juror complained to the district judge
that the word “GUILTY” had mysteriously appeared
written in the notebook she had been using during the
trial. The anonymous message, she reported, intimidated
her. The district court immediately interviewed the juror
to make sure that she could remain impartial; it then
2                                             No. 06-2180

issued a cautionary instruction to the rest of the jury.
Later, it denied Vasquez-Ruiz’s motion for a mistrial.
  On February 25, 2002, the jury found Vasquez-Ruiz
guilty on all counts of the indictment; he was sentenced on
September 11, 2002, to a term of 168 months’ imprison-
ment, and the court entered judgment on October 21, 2002.
At that point, Vasquez-Ruiz’s attorney neglected to file a
direct appeal. On February 18, 2005, the district court, in
response to a motion under 28 U.S.C. § 2255, ruled that
the lawyer had rendered ineffective assistance. After a
few more procedural adjustments, the court entered a
fresh judgment, from which Vasquez-Ruiz took a timely
appeal. Before this court, Vasquez-Ruiz challenges both
the judge’s refusal to grant a mistrial and a number of
factual findings made by the district judge at sentenc-
ing. We conclude that this incident gave rise to a presump-
tion of prejudice to the defendant, and that the evidence
was insufficient to rebut that presumption. Under these
circumstances, it was error for the court to refuse to
declare a mistrial. We reverse Vasquez-Ruiz’s convic-
tion and remand for the new trial that he requested.


                            I
  Vasquez-Ruiz began practicing medicine as a general
practitioner in Illinois in 1987. He is a native of Panama
and attended medical school in Brazil; because of his
ethnic background and fluency in Spanish, the majority of
his patients are Hispanic. In 1996, Vasquez-Ruiz began
serving patients at a clinic that was then called Medicorp.
(Medicorp later changed its name to Strategic Group
Limited, but we can safely ignore that fact.) Among
other services, the clinic offered free health screenings,
including free cholesterol and diabetes tests, at local
grocery stores in and around Chicago. Often patients were
approached in the stores and offered the free services;
No. 06-2180                                                3

some were contacted over the telephone and encouraged
to have testing done. Patients who participated in the
screenings could receive their results at the clinic.
Medicorp facilitated clinic visits by offering free transpor-
tation.
  When patients came in to the clinic for their test re-
sults or an examination, they began by filling out question-
naires regarding their medical histories. Vasquez-Ruiz
would then conduct his own interview with the patient,
focusing on what he called “the most common diseases or
disorders in Hispanic patients” such as diabetes, hyperten-
sion, hepatitis, and heart problems. After completing
the interviews, Vasquez-Ruiz would examine the patients
for ailments such as lower back pain, gallstones, urinary
tract infections, allergies, and nerve problems. Frequently,
he would recommend that a patient undergo tests in-
cluding nerve conduction velocity (“NCV”) and somato-
sensory evoked potential (“SSEP”) tests, which are used
primarily to evaluate symptoms of nerve degeneration
such as numbness, tingling, burning or weakness in the
arms and legs. As was proven at trial, and as Vasquez-
Ruiz later admitted in an interview with a special agent
from the Department of Labor, Lynn Mares O’Dea,
Vasquez-Ruiz prescribed these tests for a remarkably high
number of patients knowing that they were medically
unnecessary. He lied to patients, telling them that the
tests were necessary, and he caused false entries to be
made in their medical records, with false descriptions of
complaints and symptoms like numbness or pain in the
extremities to make the tests seem justified. Vasquez-Ruiz
also submitted fraudulent bills to insurers, seeking
reimbursement for the medically unnecessary tests. Some
of the patients were completely healthy and the tests
were nothing worse than superfluous, but fairly innocu-
ous, annoyances. Others actually had serious medical
problems entirely unrelated to any nerve issues (like
4                                               No. 06-2180

gallstones), which went untreated because Vasquez-Ruiz
convinced them that they just needed a nerve test.
  Vasquez-Ruiz was ultimately charged with seven counts
of mail fraud, in violation of 18 U.S.C. § 1341, and twenty
counts of healthcare fraud, in violation of 18 U.S.C. § 1347.
A jury trial began on February 13, 2002. Nine days later,
after the close of evidence, one of the jurors—Elva Diaz,
the only Hispanic member of the jury—informed the
district judge that someone other than herself had written
the word “GUILTY” in capital letters in the notebook
in which she had been taking notes throughout the trial.
Diaz claimed that the mysterious notation made her
feel threatened.
  The district judge immediately brought the issue to the
parties’ attention and identified two concerns raised by the
existence of the note: that Juror Diaz herself may have
been influenced by the mysterious writer, and that some-
one else, perhaps another juror, may have prejudged the
case and was potentially trying to sway others on the
jury. The district court and the parties attempted to
identify the author of the note. The court noted that the
notebooks had been left in the jury room overnight and
that the only person with access to that room was the
cleaning person, who was unlikely to have written in the
notebook. At that point, the judge stated that it was
his “governing assumption” that another juror had writ-
ten the note. The court first questioned Diaz about the
note. She stated that she noticed it for the first time the
previous day while taking notes during the defendant’s
testimony. She said that she had no idea who wrote the
note and had not spoken with any other members of the
jury about it. Asked whether she had been keeping her
notebook in the jury room overnight, she replied, “Well,
sometimes—overnight, over here in that room.” The
district court asked Diaz whether she would be able to
put the event out of her mind and decide the case based
No. 06-2180                                               5

on the law and the evidence without feeling threatened.
Diaz answered, “It’s going to be hard, but yeah, I think I
can do it.” Given the opportunity by the district judge,
neither side wanted Diaz excused from the jury.
  The district judge investigated the possibility that the
notation was left over from the notebook’s use in a previ-
ous trial. Prior to this case, the court would reuse note-
books by tearing used pages out after each trial. Diaz’s
notebook was new, however, and the notation appeared
somewhere in the middle, making it unlikely that a prior
user had written the word, except for the remote possi-
bility that a prior juror had simply written nothing but
his or her verdict in the middle of the notebook. That
possibility was made even less realistic by the fact that
the word “GUILTY” appeared on the very next page
after the one on which Diaz had finished writing the day
before she noticed it. The district court then tried to
compare the handwriting of the word “guilty” with that of
the jurors’ questionnaires, but it failed to detect anything
conclusive. At that point, Vasquez-Ruiz moved for a
mistrial.
  The court denied the motion on two grounds. First, the
judge stated that “it’s not at all clear that this was done
by another juror.” Second, the court believed that a
curative instruction to the entire jury would be sufficient.
Accordingly, the judge instructed the jury as follows:
    Ladies and gentlemen, I need to discuss something
    with you . . . that it’s come to my attention that
    something turned up in one of the juror’s notebooks
    that it’s conceivable might have been written in there
    by another juror in the case, and if so, that might
    suggest that somebody might have potentially made
    up their mind about the result of the case already.
    I don’t know if that’s the case, but that’s—as I said,
    those are the possibilities.
6                                               No. 06-2180

       I want to repeat something that I said to you the
    first ten minutes you came in here and that I then
    again repeated to you at the beginning of the trial, and
    I really want to do this in the strongest possible terms.
    It is vitally important, and; that is, that the defendant
    in this case is presumed to be innocent of the charges,
    and he is every bit as presumed innocent right now as
    he was at the beginning of the case. In fact, the in-
    struction that I will give you once the arguments are
    over will say that the presumption continues not just
    throughout the trial but during your deliberations and
    that it cannot be overcome unless you find unani-
    mously that the government has proved beyond a
    reasonable doubt that the defendant is guilty. And
    I need to tell you that if there is anyone on the jury,
    including the alternates, that has even the slightest
    hesitation of your ability to follow that instruction,
    you have not just frankly a moral obligation but you
    have a legal obligation to tell me that. And even if you
    don’t tell me that right now, you have an obligation to
    tell me that, you know, by some sort of a note at the
    next break in the case. So does everybody understand
    what I’m saying to you?
After deliberations had begun, the district court reminded
the jurors:
    [I]t’s important that your deliberations and your
    decisions all occur within the context of all 12 of you
    being in the jury room discussing the case. If anyone
    attempts to contact you or if anyone in the past has
    given you any notes, attempted to contact you or
    anything at all, it’s important that you give a note to
    the officer so that I have that and I am aware of it.
  On February 25, 2002, Vasquez-Ruiz was convicted of
all charges. He appeals the district court’s denial of his
motion for a mistrial. Additionally, he challenges a num-
ber of factual findings made at sentencing.
No. 06-2180                                               7

                            II
  Vasquez-Ruiz’s primary argument on appeal is that
the district court mishandled the situation involving
Juror Diaz and should have granted his motion for a
mistrial on the ground of the apparent presence of juror
bias. He challenges the district judge’s decision not to
conduct voir dire of each juror to ferret out the person
who wrote “GUILTY” in Diaz’s notebook. The district
court, he claims, abused its discretion when (as Vasquez-
Ruiz sees it) it concluded that it lacked the authority to
conduct individualized voir dire. Vasquez-Ruiz also
argues that even if the district court was aware of its
ability to conduct individualized voir dire, it erred by
deciding not to do so.
  The government responds first that Vasquez-Ruiz
forfeited this issue because he did not ask the district
judge to question each juror individually; this court’s
review, the government insists, can be only for plain error.
But this argument assumes that it was Vasquez-Ruiz’s
burden to ask for the individualized voir dire. In our view,
all that Vasquez-Ruiz had to do was move for a mistrial
(which he did); it was the government’s burden to try to
show that the apparent interference with Juror Diaz’s
autonomy was harmless. The proper standard of review
is thus the familiar abuse of discretion standard, which
is the one we use to review an order denying a motion for
mistrial based on juror bias. See United States v.
McClinton, 

, 1186 (7th Cir. 1998). We have
previously recognized that “[t]he management of juries
traditionally lies within the sound discretion of the trial
judge.” United States v. Wiesner, 

, 1269 (7th
Cir. 1986); see also United States v. Dominguez, 

, 1246 (11th Cir. 2000). A mistake of law is automati-
cally an abuse of discretion. See United States v. Jaderany,

, 994 (7th Cir. 2000).
8                                              No. 06-2180

  There are a number of aspects of this record that give
us grave concern. First is the content of the note. Nothing
could be more central to the jury’s function than an
opinion on ultimate guilt or innocence. This note is there-
fore nothing like the excerpt from the American Judicature
Society that one juror read to her fellows in United States
v. Warner, 

(7th Cir. Aug. 21, 2007). That
article emphasized the “sanctity of the deliberative pro-
cess” in the most general terms. 

This note, in
contrast, looked like a direction to Juror Diaz about how
she should vote in Vasquez-Ruiz’s case. Second is the
district court’s assumption that the note could have been
written only by another juror or a member of the court-
house cleaning staff. True, those are two logical possi-
bilities, but the third is that another person might have
obtained access to Diaz’s notebook and tried to interfere
with the jury’s deliberations. This possibility went largely
unexplored before the district court, probably because
everyone assumed that the security measures that had
been taken with the notebooks (in particular, locking
them in the jury room at night) had successfully insulated
them from outside contact. But Juror Diaz herself was
not able to say unequivocally that she had never taken
the notebook out of the courthouse. Moreover, the court’s
investigation indicated that the handwriting did not
appear to match that of any of the jurors. Even if it was
unlikely that the court cleaning staff would have made
such a notation, one cannot say that this was an impos-
sibility.
   What we are left with is the district court’s implicit
finding of fact that Juror Diaz herself was not the person
who wrote “GUILTY” in the notebook. Logically, therefore,
it was another person, either from the jury or from outside.
If the note was written by an outsider, then we must
analyze what happened using the line of cases that
govern external influences on a jury. The Supreme Court
No. 06-2180                                                9

has held that such influence is presumptively prejudicial.
See Remmer v. United States, 

(1954); see
also 

. That presumption can be rebutted
by the government (and we found that it had been in
Warner, see 

at *11), but there must be
some basis in the record to find rebuttal. The record here
is, in our view, inconclusive.
  First, the district court decided that it was too risky to
question the other jurors about the incident, saying:
    I’m really not—I think it would be—I think it would be
    a mistake to question people. I don’t think I can do
    that. I don’t think I can start questioning jurors in the
    middle of a trial.
Although we do not interpret this statement as an indica-
tion that the judge erroneously thought that he lacked
authority to question individual jurors, it certainly shows
that he thought that questioning was a bad idea in this
case. But this left a void in the record. Under Remmer, the
burden is on the government to rebut the presumption of
prejudice from an external influence on the 

. We see no way that the government can satisfy
that burden without developing all the information.
   District court judges have broad discretion to choose
how to handle different problems that arise with juries.
We will reverse only if they stray beyond these generous
boundaries. But, as we have noted from time to time,
“deference” does not mean “total acquiescence.” The court
recognized that the note raises two general concerns. The
first is that Diaz may have been intimidated or somehow
influenced improperly by its appearance in her notebook.
The second set of issues relates to the content of the
note. Vasquez-Ruiz argues that the note evinces racial
bias, since the only juror to find such a note was also the
only Hispanic on the jury. He suggests that the writer
“may have been motivated by the assumption that [Diaz]
10                                              No. 06-2180

was likely to find in favor of Vasquez-Ruiz due to their
shared ethnic background.” Once again, although this
may be speculation, the real question is the legal one of
who bears the risk of uncertainty in this situation—the
prosecution or the defendant? On the assumption that
someone external to the jury wrote this word, we read
Remmer as holding that it is the prosecution.
  The only remaining question is whether the same
analysis should apply if the author of the note was really
another juror who had prematurely concluded that
Vasquez-Ruiz is guilty. (We stress again that this is just
a guess, even if it may seem like the more likely possi-
bility.) Vasquez-Ruiz urges that the district judge should
have conducted voir dire with each member of the jury
in an effort to determine the note’s origin and purpose, and
that his failure to do so is reversible error. He relies
heavily on McClinton for the proposition that “the District
Court’s failure to conduct individual voir dire . . . consti-
tuted an abuse of discretion.” In McClinton, two jurors
were overheard by others on the jury making potentially
racist comments. The comments also appeared to indicate
that at least one of the jurors had prejudged the guilt of
the defendants, who were African-American. One of the
defendants moved for a mistrial. The district judge dealt
with the situation by questioning each of the jurors
individually. She asked “whether they had any personal
knowledge of the conversation, heard any other statements
of this sort, shared any of these beliefs about
African-Americans, or had any bias or prejudice toward
African-Americans.” 

. The
court additionally inquired whether “the statements
influenced the jurors in any way; whether they could
keep an open mind about the defendants’ guilt or inno-
cence; and whether they could not be impartial for any
reason.” 

process, the judge was able to determine
which jurors had made the inappropriate comments and
No. 06-2180                                               11

what the comments meant. She then excused one of the
jurors and admonished the rest “about the importance
of keeping an open mind,” 

the defendant’s
motion for a mistrial.
  On appeal, this court considered whether the district
court abused its discretion by not declaring an immediate
mistrial. In affirming the lower court’s decision, we
held that the district judge’s handling of the situation
and specifically the decision to question individual jurors
was “a reasonable response to a difficult situation . . .
[and] therefore was not an abuse of her discretion.” 

The broader point here is that the district court’s
actions resulted in the development of a record that
enabled both that court and this one to evaluate the
degree of prejudice that had developed, and to come to
a reasoned conclusion on the question whether the cura-
tive steps were adequate. We are not saying, in this
connection, that there is an ironclad requirement that
individualized voir dire is always necessary. To the
contrary, we have recognized in the past that
    [n]ot every allegation of jury misconduct is sufficiently
    substantial or sufficiently well substantiated to
    warrant putting the jurors on the spot in this fash-
    ion. . . . Quizzing a juror, or perhaps all the jurors, in
    the middle of a trial is likely to unsettle the jury, and
    the judge is not required to do so unless there is a
    much stronger indication of bias or irregularity than
    there was here.
United States v. Stafford, 

, 1112-13 (7th Cir.
1998). Some allegations of misconduct might not warrant
individualized voir dire and others will; other information
may already be in the record that makes this kind of
inquiry unnecessary. Here, where a mysterious note
simply appears in a juror’s notebook, and where we cannot
even say with assurance that it was another juror who
12                                               No. 06-2180

wrote the note in the first place, there was a need to make
a greater effort to find out what had happened before
declaring that it did not make any difference. Such
an investigation would not necessarily involve questioning
the other jurors (an option the district judge rightly
thought held its own risks), but as a last resort such a step
may be unavoidable.
  It is true that the district court tried to address the
situation by giving a curative instruction. We have previ-
ously found a curative instruction to be sufficient in an
instance of serious jury misconduct. In United States v.
Read, 

(7th Cir. 1981), the trial judge
received a note from a juror before the jury had begun
its third day of deliberations:
     According to the letter, most of the jurors made up
     their minds by the second week of trial (the trial lasted
     at least seven weeks); many completely disregarded
     the judge’s instructions that the jurors not look in the
     newspaper financial sections and made a point of
     examining Cenco stock [in a securities fraud case];
     many of these jurors refused to deliberate or discuss
     the case, claiming “all these guys are guilty,” and
     instead worked on crossword puzzles, and several of
     the jurors thought the whole trial was hilarious
     and laughed at the 

. The court denied the defendant’s motion
for a mistrial. Instead, it chose simply to read a cautionary
instruction to the entire jury and interviewed the juror
who sent the note after the jury had returned a verdict
against the defendant. 

this court noted that
the trial judge was “in the best position to sense the
atmosphere of the courtroom as no appellate court can on
a printed record.” 

omitted). We
concluded that the district judge “properly exercised his
discretion in responding to the allegations,” and affirmed
the denial of the motion for mistrial. 

No. 06-2180                                               13

  Vasquez-Ruiz argues that his case is more like United
States v. Resko, 

(3d Cir. 1993), than it is like
Read. In Resko, seven days into a nine-day trial the
judge learned that jurors had been discussing the case
among 

. The defendants asked
the court to conduct individualized voir dire to determine
the nature of the conversations that took place and the
extent of any possible prejudice to the defendant caused
by the premature deliberations. 

They also
moved for a mistrial. In lieu of individualized voir dire,
the court had each juror fill out a questionnaire, which
asked whether he or she had discussed the case. Every
juror answered in the affirmative, although nobody
claimed to have reached a conclusion on guilt or inno-
cence. Concluding that the defendants suffered no preju-
dice, the court denied the motion for mistrial.
  The Third Circuit reversed on appeal. Although the
court recognized “a clear doctrinal distinction between
evidence of improper intra-jury communications and
extra-jury influences” and that “[i]t is well-established
that the latter pose a far more serious threat to the de-
fendant’s right to be tried by an impartial jury,” 

it concluded that simply handing out the questionnaire
without any follow-up “was inadequate to enable the court
to fulfill its responsibility of providing an appropriate
cautionary instruction and of determining whether preju-
dice resulted from the jury misconduct.” 

  We come back, in the end, to the lack of information in
this record about the source of the notation in Juror Diaz’s
notebook. The record is too sparse to permit us to con-
clude that the government rebutted the presumption of
prejudice that arises under Remmer, on the assumption
that the writer was someone not on the jury. Even if the
writer was another juror, we agree with Vasquez-Ruiz that
this case is more like Resko than like Read. If someone
14                                              No. 06-2180

on the jury was trying to pressure Juror Diaz into voting
to convict Vasquez-Ruiz, before deliberations began and
before the court instructed the jury, then the court might
have taken different remedial measures. Perhaps it
would have dismissed the miscreant juror; perhaps it
would have issued a different cautionary instruction;
perhaps it would have declared a mistrial. As it was,
however, we conclude that the unexplained apparent
attempt by someone to tell Juror Diaz to vote “GUILTY”
could be cured only by granting a mistrial.


                            III
  Vasquez-Ruiz also challenged several findings that the
district court made in connection with his sentencing: the
amount of loss attributable to him (U.S. SENTENCING
GUIDELINES MANUAL § 2F1.1 (1998)); the finding that his
fraud involved “the conscious or reckless risk of serious
bodily injury” (id. § 2F1.1(b)(6)(A)); the two-point enhance-
ment for committing an offense “through mass-marketing”
(id. § 2F1.1(b)(3)); and the application of the two-point
“vulnerable victim” enhancement (id. § 3A1.1(b)(1)).
Because we are remanding for a new trial, we need not
reach these points. We note only that at the time Vasquez-
Ruiz was sentenced, the Supreme Court had not yet
decided United States v. Booker, 

(2005), and
so the district court treated the Sentencing Guidelines
as mandatory. Should Vasquez-Ruiz be convicted again,
the district court will naturally treat the Guidelines as
advisory only.
  The judgment of the district court is REVERSED and the
case is REMANDED for further proceedings consistent with
this opinion.
No. 06-2180                                        15

A true Copy:
      Teste:

                   ________________________________
                   Clerk of the United States Court of
                     Appeals for the Seventh Circuit




               USCA-02-C-0072—9-17-07