                            In the

United States Court of Appeals
              For the Seventh Circuit

No. 09-2787

U NITED S TATES OF A MERICA,
                                                Plaintiff-Appellee,
                                v.

M ARK C IESIOLKA,
                                            Defendant-Appellant.


            Appeal from the United States District Court
      for the Northern District of Indiana, Hammond Division.
               No. 2:06 cr 163—Rudy Lozano, Judge.



       A RGUED A PRIL 21, 2010—D ECIDED JULY 26, 2010




 Before C UDAHY, R IPPLE, and H AMILTON, Circuit Judges.
  C UDAHY, Circuit Judge. Mark Ciesiolka was convicted
in 2008 of knowingly attempting to persuade, induce,
entice and coerce a minor to engage in sexual activity
under 18 U.S.C. § 2422(b). His prosecution emanated
from a police sting operation, in which an officer, pur-
porting to be a 13-year-old girl named “Ashley,” engaged
in series of sexually explicit, instant-messaging (“IM”)
conversations on an online Yahoo forum with the defen-
2                                               No. 09-2787

dant. The sting, however, was marred by numerous
oddities. The profile created by the officer displayed a
photo of a woman in her late 20s and indicated that the
user’s interests included “beer” and “Purdue University.”
When asked by the defendant to send pictures during
their IM conversations, the officer inexplicably sent a
photo of a woman in her late 20s. Ciesiolka remarked
that she looked 21. Ashley nevertheless maintained that
she was just 13. Although Ciesiolka and the officer
agreed to meet at a Pizza King, the defendant evidently
got cold feet and, despite repeated encouragement from
Ashley, declined to meet. The officer admitted: “I lie
about my age.”
  The crime with which Ciesiolka was charged required
the government to prove beyond a reasonable doubt
that the defendant believed that “Ashley” was under 18.
We find that the district court improperly relieved the
government of that burden by providing the jury with
an ostrich instruction. Moreover, given the somewhat
bizarre nature of the sting operation itself, replete as it
was with suggestions that Ashley may have been an
adult, it is perhaps unsurprising that the government
sought to bolster its case. It did so by introducing volumi-
nous evidence under Fed. R. Evid. 404(b) of the de-
fendant’s other IM conversations with unknown third
parties, over 100 images of child pornography and/or
erotica discovered on his computer and testimony from
a woman, “SC,” who claimed that Ciesiolka had had sex
with her several times when she was 15. This evidence
took up an entire day of a three-day trial and yet, at
the time of its introduction, was subject only to a single,
No. 09-2787                                             3

pro forma limiting instruction. Because the district court
failed to explain its ruling that the four-factor test
for introducing evidence of prior acts under Rule 404(b)
was satisfied, and since the evidence introduced in uncon-
strained fashion strikes us as perhaps being excessively
prejudicial in light of its probative value, we reverse
and remand for a new trial.


                  I. BACKGROUND
  Pursuant to Indiana’s Safe Childhood Project, Detective
Sergeant Carrie Costello, an officer with the Purdue
University Police Department, initiated an Internet sting
operation to lure and prosecute pedophiles who were
operating online. The defendant in the present case,
Mark Ciesiolka, walked right into the trap. On August 2,
2006, he encountered a person by the name of “Ashley”
in a Yahoo adults-only chat room, entitled “Indiana
Romance.” Ashley’s Yahoo profile photo was of a
woman in her 20s (a fellow police officer) and her stated
interests included “Purdue University” and “beer.” The
profile did not state her age.
  Starting on August 2 and proceeding over the following
two-and-a-half weeks, Ciesiolka and Ashley exchanged
numerous, sexually explicit IM messages. At trial, those
messages were read aloud to the jury by officer Costello,
playing herself, and by special agent Christian Ebel-Orr,
playing the role of Ciesiolka. The defendant and Ashley
informed each other that they lived in Columbus and
Lafayette, respectively. He asked her why she was in a
forum for married people. He inquired as to whether her
4                                               No. 09-2787

mom and dad were home, and asked whether she had a
boyfriend. Somewhat oddly, in response to Ciesiolka’s
request for pictures of herself, Ashley sent a different
photo of the same woman in her late 20s whose picture
adorned Ashley’s online profile. Ciesiolka responded that
she looked 21 or so. Ashley, however, maintained that
she was only 13.
  The defendant asked Ashley whether she was a virgin
and whether she masturbated. She feigned the lack of
knowledge one might expect of a 13-year-old, saying that
she “think[s] so . . . means no sex, right?” As to masturba-
tion, she wrote “[n]ot sure what that is.” During ensuing
conversations, the defendant requested more photos;
Ashley repeatedly asked to see him on his web cam.
Ashley told him she’d gotten in trouble for staying over
at a friend’s house where her friend had gotten some
beer. When asked how much she drank, Ashley ex-
plained: “I didn’t. Don’t like the taste of beer, really, but
everyone else did, so I got in trouble.” Later, Ashley
wrote that she doesn’t usually wear panties, but when
she does they’re thongs. The defendant subsequently
provided her with instructions on how to masturbate.
Ashley referred to her mother’s being “40 something.”
When asked whether she shaves, she replied that
there’s “[n]ot much to shave.” The defendant exposed
himself and masturbated via his web cam during an IM
exchange. He later asked whether it was sad that he was
“looking to a younger lady to tell [him] that [he was]
still sexy.”
 Following these IM conversations, which were both
more explicit and offensive than the preceding summary
No. 09-2787                                             5

might suggest, the talk eventually turned to meeting up.
Ciesiolka said: “I would come see you but might get
in trouble.” He and Ashley ultimately agreed to meet at
a Pizza King at 5 o’clock on Friday, August 18. This
seemed like an opportune time, since Ashley said that
her mother was leaving that Friday for the weekend
to attend a wedding. Ashley said that she would tell
her mom that she was meeting friends to eat. Later,
the defendant asked Ashley if she’d mind if he brought
his 12-year-old son with him to their meeting. He asked
whether she’d have sex with him and explained that
he’d teach both of them. On August 14, Ciesiolka asked
whether “she was going to tell on [him],” explaining that
he “would get into really big trouble.”
  Despite the arrangement, Ciesiolka never showed up
on August 18. In a subsequent message, the defendant
explained to Ashley that he couldn’t meet with his son
there, since he believed his son would tell. Ashley then
wrote: “I lie about my age.” When Ashley subsequently
referenced her upcoming birthday, Ciesiolka asked:
“You will be 15?,” to which Ashley responded “14.”
  Following the last IM conversation, the authorities were
able to track down the defendant, who was arrested on
August 19. During the ensuing trial, the government
introduced evidence of Ciesiolka’s prior bad acts under
Fed. R. Evid. 404(b). This included other IM conversa-
tions the defendant had had with unidentified third
parties—exchanges that were replete with lewd and
offensive details. The jury was also shown approximately
100 images of child pornography or “child erotica” that
6                                                No. 09-2787

had been found on the defendant’s computer. In addi-
tion, the jury heard testimony from a woman to the
effect that the defendant had had sex with her numerous
times when she was 15 years old.
  The content of his IM conversations with Ashley, in
conjunction with the Rule 404(b) evidence introduced
by the government at trial, makes clear that Ciesiolka is,
at the very least, a potentially dangerous individual. But
that fact does not translate into our affirming his ensuing
conviction. Because we find numerous errors in the
district court’s handling of the present case, and since
we cannot confidently conclude that these errors were
harmless, we reverse and remand for a new trial.


                      II. DISCUSSION
    A. The District Court Erred in Providing the Jury with an
       Ostrich Instruction
  A focal point of Ciesiolka’s appeal concerns his
strenuous objection to the district court’s jury instruction
number 18 (the “ostrich instruction”), which provided:
     You may infer knowledge from a combination of
     suspicion and indifference to the truth, if you find
     that a person had a strong suspicion that things
     were not as they seemed or that someone had with-
     held some important facts, yet shut his eyes for fear
     of what he would learn, you may conclude that he
     acted knowingly, as I have used that word. You may
     not conclude that the Defendant had knowledge if he
     was merely negligent in not discovering the truth.
No. 09-2787                                                 7

  Ciesiolka contends that this instruction served to
relieve the government of its obligation to prove beyond
a reasonable doubt that he believed that Ashley was a
minor. He argues that the instruction allowed the jury
to convict him based merely on his suspicion of, and
indifference to, Ashley’s being underage. Ciesiolka also
contends that an ostrich instruction has no proper ap-
plication to the present setting, where learning the
“truth” would have revealed that “Ashley” was an adult
police officer. Of course, discovering that truth from the
outset would have resulted in Ciesiolka’s not having
violated 18 U.S.C. § 2422(b).
  We are thus faced with the question whether the ostrich
instruction was appropriately given to the jury. This
specific question, arising in the context of 18 U.S.C.
§ 2422(b), is a matter of first impression for this court.
  An ostrich instruction obviously fits somewhat awk-
wardly with a sting operation of the kind presented by
this case. Such an instruction is typically employed to
capture individuals who deliberately close their eyes to
the truth. See United States v. Carani, 492 F.3d 867, 873 (7th
Cir. 2007). We have approved the use of ostrich instruc-
tions in a few cases involving police undercover or “sting”
operations, but only in limited circumstances and while
recognizing the danger that such instructions could
relieve the government of its burden of proving the
elements of an offense beyond a reasonable doubt. For
example, in United States v. Kaufmann, 985 F.2d 884, 896-97
(7th Cir. 1993), the defendant was charged with four
money laundering counts involving real criminals with
8                                                 No. 09-2787

money from real criminal dealings, but he was not con-
victed on those charges. He was convicted only on one
charge of attempted money laundering, which involved
an undercover agent’s planned purchase of a sports car
for cash using a straw purchaser. We held that an
ostrich instruction was appropriate for the first four
counts. The jury instructions distinguished between
knowledge for the first four counts and the belief
required to convict on the sting count. Those steps pre-
vented the jury from being misled into finding “belief” on
the fifth count by finding only strong suspicion plus
indifference to the truth. Id. at 896-97.
  Similarly, in United States v. Wilson, 134 F.3d 855 (7th Cir.
1998), the defendant was caught in a sting operation in
which he delivered real cocaine, but he denied knowing
that the bags contained cocaine. We affirmed the use of
an ostrich instruction under those circumstances, where
the truth the defendant denied was actually incriminating
rather than exonerating. Id. at 868-69. And in United
States v. Inglese, 282 F.3d 528 (7th Cir. 2002), the de-
fendants were convicted of selling firearms to under-
cover agents posing as customers with felony convictions
that barred them from lawful purchases. We affirmed
the use of an ostrich instruction where there was ample
evidence that the agents had made it clear that the
sales would be illegal. Id. at 537-38. The use of a straw
purchaser for firearms was illegal even if the “customers”
were undercover agents.
  These narrow uses of ostrich instructions do not
extend to the circumstances of this case, in which knowl-
No. 09-2787                                                9

edge of “Ashley’s” real age would have exonerated the
defendant rather than incriminated him. We have not
approved the use of an ostrich instruction that applied
to a defendant’s mistaken belief about circumstances
where knowledge of the truth would exonerate a defen-
dant, such as “Ashley’s” true age in this case or the
fact that the suspicious substance was baking powder
rather than cocaine in another sort of case. If a district
court gives an ostrich instruction in sting cases, it must
take great care to ensure that the jury understands that
the instruction should not be applied to issues as to
which a defendant’s knowledge of the real truth would
actually exonerate him. In this case, the principal issue
in dispute, if not the only one, fits that description. Ac-
cordingly, we find that it was error to give the ostrich
instruction in this case.
  Even if the ostrich instruction might otherwise have
been proper, there is a second problem with its use in
this case. We have previously made clear that such
an instruction must be given cautiously, lest a jury im-
properly convict a defendant on the basis of negligence.
See United States v. Carrillo, 435 F.3d 767, 781 (7th
Cir. 2006). Of course, ostrich instructions bearing the
potential for misapplication does not mean they are
categorically improper. We have explained that they are
appropriately given to a jury when: (1) a defendant
claims a lack of guilty knowledge and (2) the govern-
ment presents evidence that suggests that the defendant
deliberately avoided the truth. See United States v. Garcia,
580 F.3d 528, 537 (7th Cir. 2009). Ciesiolka claims a lack of
guilty knowledge; thus, the issue is whether the gov-
10                                                 No. 09-2787

ernment introduced sufficient evidence that he remained
deliberately ignorant, thus justifying the instruction. See
id. It is with respect to this second requirement that the
government runs aground.
   Reviewing the record, we do not see what steps the
defendant avoided taking to make sure he did “not
acquire full or exact knowledge” of Ashley’s age. See
United States v. Giovannetti, 919 F.2d 1223, 1228 (7th Cir.
1990); cf. United States v. Inglese, 282 F.3d 528, 537 (7th Cir.
2002). There is little evidence, which we can discern, that
suggests that avenues open to Ciesiolka to confirm
Ashley’s age remained unavailed of. Defendant did not
try to hide from knowledge about Ashley’s age—he
repeatedly raised the issue with her and received con-
flicting information. He asked her her age. Reminded
that her birthday was coming up, he asked her whether
she would be 15. She corrected him, saying that she
would be 14. He asked her whether her parents were
home. He impressed upon her the importance of her not
telling anyone about their conversations or potentially
meeting up. She told him about her lack of sexual experi-
ence and that her mother was “forty something.” All
this inculpatory evidence goes to Ciesiolka’s belief as to
Ashley’s age. But none of it suggests that Ciesiolka delib-
erately closed his eyes as to her age; it rather appears that
he took active steps to discover it. Beyond the previous
examples, including the obvious one of his actually
asking her her age, he asked for pictures of her. When
presented with a photo of a woman in her 20s, he took
positive steps to inquire as to her age, observing that she
No. 09-2787                                                   11

looked 21, and perhaps 18 or 19. She assured him that
she was only 13. These are not the acts of a person who
deliberately avoids learning the truth.
  Complicating matters further, defendant argues that
he thought “Ashley” was an adult woman pretending to
be a 13-year-old girl to play along with his fantasies.
Some evidence lends support to this argument. Ashley’s
profile photo was that of an adult woman in her late 20s.
Her stated interests included beer and Purdue University.
Perhaps the most perplexing feature of the present case
is that, in response to Ciesiolka’s request for pictures of
her, Ashley sent another photo of the same adult woman
who adorned her Yahoo profile. One strains to under-
stand why a police officer in a sting operation of this sort
would send such a picture, which at best would serve to
inject confusion, uncertainty and suspicion as to the
“victim’s” age. In fact, it could surely have led Ciesiolka
to believe that “Ashley” was an adult, pretending to be
younger than she was. 1 The unusual circumstances may


1
   When pressed at oral argument to explain this bizarre
move, counsel for the United States explained that the officer
could not in good conscience have sent a picture of an actual
child to Ciesiolka, knowing full well what the defendant would
have used the picture for. This does not change the fact that the
police officer would have been far better off not sending any
photo whatsoever instead of sending the picture that she did.
If she felt compelled to send some photo, however, she could
presumably have sent an old one of herself or one of her fellow
officers as a child. None of these avenues would seem to
                                                   (continued...)
12                                              No. 09-2787

even have led the defendant to suspect that Ashley was
in fact a police officer, which would be consistent with
his failing to appear at the agreed time and his subse-
quent reluctance to interact with her.
  On this record, with its conflicting information about
Ashley’s age, and at least apart from the quantity of
evidence admitted under Rule 404(b), defendant’s argu-
ment that he believed Ashley was an adult pretending
to be 13 years old has some evidence to support it. As
a result, the ostrich instruction could have invited the
jury to convict the defendant based on mere suspicion
and indifference as to her true age, where knowledge of
her true age would have exonerated him rather than
incriminated him.
  The lack of evidence in the record suggesting Ciesiolka’s
taking steps not to acquire knowledge of Ashley’s age
also renders the district court’s ostrich instruction errone-
ous. The effect of the instruction was indeed to enable
the jury to convict Ciesiolka not because it determined that
he believed that Ashley was under 18, but because it
concluded that he was suspicious and indifferent to
whether she was underage. We therefore agree with
the appellant that this served improperly to relieve the
government of its burden of proof.




1
  (...continued)
have presented ethical issues of the sort deemed controlling
by counsel at oral argument.
No. 09-2787                                                13

  Such an error does not necessarily require us to vacate
the conviction and sentence imposed by the district court,
however. Instead, we must determine whether the error
was harmless. We will reach that conclusion “if the evi-
dence is so strong that a jury would have reached the
same verdict absent the erroneous instruction.” United
States v. Ramsey, 406 F.3d 426, 432 (7th Cir. 2005). It is
possible that an erroneously provided ostrich instruc-
tion can be harmless. United States v. Nobles, 69 F.3d 172,
187 (7th Cir. 1995).
  We cannot confidently conclude that the erroneous
instruction was harmless in the present case. We are
mindful of the risk that our relying on the weight of the
evidence alone to determine harmless error may involve
our usurping the function of the jury. See United States
v. Peak, 856 F.2d 825, 835 n.7 (7th Cir. 1988); see also Obrey
v. Johnson, 400 F.3d 691, 701 (9th Cir. 2005); Burkhart
v. Washington Metropolitan Area Transit Authority, 112
F.3d 1207, 1218 (D.C. Cir. 1997) (Edwards, C.J., concurring).
   Although there is sufficient inculpatory evidence for
a jury to find that Ciesiolka believed “Ashley” was a
minor, the evidence certainly does not compel that con-
clusion. In so holding, we would seem to part company
with the dissent, which contends that the “transcripts
of the conversations between Mr. Ciesiolka and ‘Ashley’
gave the jury a very firm basis for concluding that
Mr. Ciesiolka believed Ashley was a minor.” Dissent at 24.
It seems to us that “a very firm basis” is far from synony-
mous with “conclusive.” Cf. United States v. Hatfield, 591
F.3d 945, 951 (7th Cir. 2010) (remanding for retrial because
14                                              No. 09-2787

the “evidence . . .[,] though strong enough to justify a
verdict of guilt beyond a reasonable doubt, was not
conclusive”). In any event, we do not believe that the
transcripts of the IM conversations between Ciesiolka
and Ashley provide conclusive evidence that the
defendant believed he was in fact conversing with a
minor. Indeed, the government’s case against the defen-
dant was beset by numerous and obvious problems, not
the least of which were Ciesiolka’s commenting that
Ashley looked 21 or so, as well as Ashley’s profile photo
and the photo she sent the defendant being those of an
adult woman in her late 20s, in addition to her stated
interests in beer and Purdue University.
  As the Supreme Court has instructed, the relevant
question must be: “Is it clear beyond a reasonable doubt
that a rational jury would have found the defendant
guilty absent the error?” Neder v. United States, 527 U.S. 1,
18 (1999). Given the significance of the error in intro-
ducing a jury instruction that relieved the government
of its burden of proof, in addition to the exculpatory
evidence just noted, we cannot answer this question in
the affirmative.
  It is only when one embraces the extravagantly profuse
indications of the defendant’s prior bad acts introduced
under Rule 404(b) that his guilty intent and knowledge
become more plausible. It is unsurprising, then, that
the dissent is forced to focus almost exclusively on this
Rule 404(b) evidence. Indeed, the dissent’s approach is
much like that of the government, which made up for an
evidentiary shortfall concerning the crime charged by
No. 09-2787                                              15

spending a full day of a three-day trial showcasing the
defendant’s alleged bad acts in front of the jury. As we
explain below, we have grave concerns about the manner
in which the district court allowed this evidence to be
introduced. Since we conclude that the district court failed
adequately to explain its reasoning in applying the
Rule 404(b) factors before allowing the evidence to be
admitted, we will not use this prior-act evidence to find
that the district court’s mistaken ostrich instruction
was harmless.
  In light of the relevant evidence, there is a distinct
likelihood that the jury convicted Ciesiolka based on his
being merely suspicious and indifferent about Ashley’s
age, rather than on a factual determination, beyond a
reasonable doubt, that the defendant believed Ashley
was a minor. We therefore reverse the judgment and
sentence of the district court and remand for a new trial.
As we now explain, this conclusion is bolstered by the
district court’s handling of the government’s Rule 404(b)
evidence.


  B. The District Court Erred in Failing to Explain its Rea-
     soning in Admitting Highly Prejudicial Evidence Under
     Fed. R. Evid. 404(b)
  Ciesiolka contends that the profuse evidence of his prior
bad acts was improperly admitted under Fed. R. Evid.
404(b), which requires reversal. In considering this argu-
ment, it is important that we delineate precisely the
legitimate ends to which the evidence could be applied. It
is black-letter law that the government cannot introduce
16                                                No. 09-2787

evidence of a defendant’s prior bad acts to show her
propensity to commit the charged crime. See Fed. R. Evid.
404(a); United States v. Perkins, 548 F.3d 510, 513 (7th Cir.
2008). Such evidence may be admitted, however, for non-
propensity purposes, such as “proof of motive, opportu-
nity, intent, preparation, plan, knowledge, identity, or
absence of mistake.” Fed. R. Evid. 404(b). Nevertheless,
evidence sought to be introduced for one of these legiti-
mate purposes will not be admitted if the evidence fails
to meet the requirements of Rule 403. Perkins, 548 F.3d at
514. Specifically, in addition to being offered for non-
propensity purposes, the evidence must (1) show that the
prior act is similar enough and close enough in time to
be relevant to the matter in issue; (2) be sufficient to
support a jury finding that the defendant committed the
similar act; and (3) have probative value that is not sub-
stantially outweighed by the danger of unfair prejudice. Id.
  In the present case, the issue for the jury was whether
Ciesiolka believed that “Ashley” was under 18. It bears
emphasizing that 18 U.S.C. § 2422(b) requires proof of
specific intent. See, e.g., United States v. Murrell, 368 F.3d
1283, 1286 (11th Cir. 2004). It is well established that,
with specific-intent crimes, “the government may present
other acts evidence to prove intent. ” United States v. Long,
86 F.3d 81, 84 (7th Cir. 1996) (quoting United States v. Smith,
995 F.2d 662, 672 (7th Cir. 1993), cert. denied sub nom.
Marren v. United States, 510 U.S. 1056 (1994)). The
question is what limits on such evidence of “other acts”
must be invoked consistent with the strictures of Fed.
R. Evid. 403.
No. 09-2787                                                 17

  As noted above, the evidence concerning the de-
fendant’s online interaction with “Ashley” is somewhat
equivocal. The photos of Ashley were of a woman in
her 20s. She admitted to lying about her age. Ciesiolka
commented that she looked 21. Her interests, as des-
cribed on her Yahoo profile, included beer and Purdue
University. Such facts lend strong support to the defense
argument that Ciesiolka believed he was interacting
with an adult.2 It may have been the case, for instance,
that the defendant believed Ashley was an adult pur-
porting to act as a minor. If this were the case, Ciesiolka
could have gone along with the fantasy without violating
18 U.S.C. § 2422(b).
  Were the jury limited to considering direct evidence of
Ashley and Ciesiolka’s online exchanges alone, these
exculpatory facts might have been enough to create
reasonable doubt in the minds of the jury. No doubt
aware of this possibility, the government appealed
to evidence of prior bad acts to establish that the de-
fendant in fact believed he was interacting with a minor.


2
  Of course, there is considerable inculpatory evidence within
the defendant and Ashley’s IM conversations. For instance,
Ciesiolka impressed upon her the importance of not allowing
anyone to find out about their talk and plans, lest they get in
trouble. Moreover, when she noted her upcoming birthday,
he asked whether it was to be her 15th. These and other inte-
ractions suggest that the defendant believed he was sending
IM messages to a minor. The point for now, though, is that
this evidence is far from conclusive, thus presumably inducing
the government to rely heavily on Rule 404(b) evidence.
18                                                 No. 09-2787

To speak in the terms of Rule 404(b), the government
introduced this evidence to show knowledge and intent.
  In reviewing the permissibility of the character evidence
so introduced, we must distinguish between two sorts
of infirmities. First, to the extent any evidence was ad-
mitted that goes to propensity, but not to the defendant’s
knowledge or intent, then such admission was in error.
Second, even if evidence were introduced to show knowl-
edge or intent, such admission was also improper if
the prior act is not sufficiently similar, if the act’s prejudi-
cial effect substantially outweighs its probative value or
if there is insufficient evidence to support a jury’s
finding that the defendant committed the similar act. We
note from the outset that our review is for abuse of discre-
tion. In the context of Rule 403, we have given “ ‘special
deference’ to the district court’s findings and reverse
only when ‘no reasonable person could take the view
adopted by the trial court.’ ” United States v. LeShore, 543
F.3d 935, 939 (7th Cir. 2008) (quoting United States v.
Cash, 394 F.3d 560, 564 (7th Cir. 2005)).
  Despite this deferential review, we have determined
that district courts abused their discretion in admitting
“extremely prejudicial” Rule 404(b) evidence where that
prejudicial effect is “far greater” than its probative value.
United States v. Heath, 188 F.3d 916, 922-23 (7th Cir. 1999);
see also United States v. Johnson, 584 F.3d 731, 738 (7th Cir.
2009). Importantly, we may also reverse if the district
court failed to consider the prejudicial nature of the
Rule 404(b) evidence before allowing it to be admitted. See
United States v. Macey, 8 F.3d 462, 467 (7th Cir. 1993). Such
No. 09-2787                                                19

“perfunctory” analysis is insufficient. See id.; see also
United States v. Beasley, 809 F.2d 1273, 1279 (7th Cir. 1987).
  We find that the district court abused its discretion in
failing to propound reasons for its conclusion that the
probative value of SC’s testimony, the many images of
child pornography and the content of Ciesiolka’s numer-
ous, offensive IM conversations with third parties
was not substantially outweighed by the risk of unfair
prejudice. We have reviewed the transcript of the
district court’s Rule 404(b) hearing, but could find no
portion within it where the court explained its bare-bones
conclusion that “the probative value of the evidence is not
substantially outweighed by the danger of unfair preju-
dice.”
  The dissent finds fault with this conclusion. In doing
so, it draws attention to one statement of the district
court in advance of trial and to another made in
response to the defendant’s Fed. R. Crim. P. 33 motion
for a new trial. Dissent at 25-27 n.1. But we have not, as the
dissent suggests, “give[n] far too little weight to the
district court’s post-trial ruling.” Id. at 27. Nothing in
either of these statements by the district court makes
reference to any form of prejudice to the defendant.
While it is true that the district court elucidated to
some degree the probative value of the Rule 404(b) evi-
dence, the fact of evidence’s being potentially probative
does not imply—let alone ensure—that this quality is not
substantially outweighed by the danger of unfair preju-
dice. There is no trace of an explanation as to this
crucially important consideration—one that we require
20                                                No. 09-2787

district courts to make when admitting evidence under
Rule 404(b). See, e.g., Macey, 8 F.3d at 467 (observing that
“all 404(b) evidence presents the danger that juries will
equate the prior bad act with the crime charged, and
convict the latter because of the former,” emphasizing that
“[n]owhere did the court consider the prejudicial nature
of [the challenged] testimony,” and finding error as a
result). Here, the potentially prejudicial nature of the
assorted, objectionable material was grossly enhanced
by the time (a full day) required to present it.3
  As noted, a trial court’s “perfunctory” consideration of
this critical question is inadequate and may in itself be
grounds for reversal. We have also observed that “[a] flaw
in the process is easier to detect than is a flaw in the
result” when reviewing district-court rulings under
Rule 404(b). Beasley, 809 F.2d at 1279. Here, we find a
serious flaw in the process.
  Our concern regarding the absence of any considered
explanation is magnified by our belief that the cumulative
impact of the Rule 404(b) evidence may have been unac-
ceptably prejudicial vis-à-vis its probative value. We have
previously explained that the Rule 403 standard incorpo-
rated in the requisite test for admitting evidence under
Rule 404(b) has teeth. See Beasley, 809 F.2d at 1278-79. We


3
  We note that the Rule 404(b) evidence may have been cir-
cumstantially probative in various indirect ways of Ciesiolka’s
state of mind in communicating with the officer, but it was
certainly prejudicial in broadly and deeply impugning his
character.
No. 09-2787                                              21

have emphasized that “[a] rule that a judge may admit
all evidence that the defendant committed crimes of
similar varieties produces the gravest risk of offending
the central prohibition of Rule 404(b): ‘Evidence of other
crimes, wrongs, or acts is not admissible to prove the
character of a person in order to show that he acted in
conformity therewith.’ ” Id. at 1278. We find just such a
risk present in the instant case. The district court
allowed mountains of Rule 404(b) evidence, much
of which was highly prejudicial, to be introduced in a
seemingly unconstrained way.
  The jury’s day-long exposure to voluminous evidence
of Ciesiolka’s prior bad acts, many of which were ap-
palling, created a significant risk of prejudice. There is
a real danger that such evidence, dumped without con-
straint into the record, can lead a jury to convict a defen-
dant not on the basis of proof of the crime with which
he has been charged, but for his simply being a bad person
or for having committed unseemly acts in the past. See
Macey, 8 F.3d at 467. The deluge of Rule 404(b) evidence,
which ran the gamut from the jury’s viewing over 100
images of child pornography to its hearing a woman’s
testimony of her having had sex with the defendant
when she was 15 to the offensive sexual content of defen-
dant’s many IM conversations with unknown third
parties, was certainly prejudicial and probably more
prejudicial than probative. Whether it was unfairly preju-
dicial is a more difficult question in light of our highly
deferential review of district courts’ Rule 403 determina-
tions, but we nevertheless feel compelled to reverse
and remand based on the court’s failure to explain its
reasoning.
22                                                No. 09-2787

  The prejudice could conceivably have been cured by
appropriate limiting instructions. See United States v.
Jones, 455 F.3d 800, 809 (7th Cir. 2006) (noting that such
instructions “are effective in reducing or eliminating
any possible unfair prejudice from the introduction of
Rule 404(b) evidence”) (quoting United States v. Best,
250 F.3d 1084, 1093 (7th Cir. 2001)). In the present case,
during the admission of the Rule 404(b) evidence, the
district court granted only one such instruction, which it
gave to the jury in boiler-plate form at the start of the
second day. The judge refused to provide any further
instructions during the introduction of Rule 404(b) evi-
dence, although repeatedly requested to do so. He did not
explain why.
  Given the extensive evidence of prior bad acts, intro-
duced over an entire day and from multiple sources, and
given the damning nature of that evidence, we are not
confident that the court’s pro forma limiting instruction
sufficiently cured the error. Cf. Johnson, 584 F.3d at 737. See
generally United States v. Smith, 308 F.3d 726, 739 (7th Cir.
2002) (“[J]urors are presumed to follow limiting and
curative instructions unless the matter improperly
before them is so powerfully incriminating that they
cannot reasonably be expected to put it out of their
minds.”). We do not hold that it was necessarily an
abuse of discretion for the district court to refuse to
repeat its limiting instruction, though it surely would
have ameliorated the situation had it done so. Compare,
e.g., United States v. Butler, 102 F.3d 1191, 1196-97 (11th
Cir. 1997) with United States v. Mounts, 35 F.3d 1208,
No. 09-2787                                              23

1215 (7th Cir. 1994) (weighing the value of the “district
court’s careful and repeated instructions to the jury”). But
we do find that, given the context-specific facts of this
highly unusual case, the district court’s failure to
explain its decision to grant the government virtual
carte blanche to introduce all the Rule 404(b) evidence
that it did was an error that was not adequately cured
by the limiting instruction provided.
  For the purposes of remand, we do not suggest that
none of the Rule 404(b) evidence introduced at trial was
properly admissible. Instead, the district court should
carefully analyze each piece of proposed Rule 404(b)
evidence to satisfy itself that the requirements for ad-
missibility are satisfied. Having done so, it should lay
out its reasoning clearly for the record.


                   III. CONCLUSION
  For the foregoing reasons, we reverse the judgment and
sentence of the district court and remand for a new trial.
Our Circuit Rule 36 shall apply on remand.
                                R EVERSED and R EMANDED.
24                                             No. 09-2787

  R IPPLE, Circuit Judge, dissenting. I agree with my col-
leagues that, under the particular facts and circumstances
of this case, the so-called ostrich instruction should not
have been given. We always have recognized that this
instruction must be employed with great caution to
avoid the possibility that a jury might convict a defendant
on the basis of negligence rather than actual knowledge.
See United States v. Carrillo, 435 F.3d 767, 781 (7th Cir.
2006). Accordingly, we have limited the use of the in-
struction to situations in which the defendant claims a
lack of guilty knowledge and the Government produces
a factual basis from which the jury might conclude that
the defendant deliberately avoided the truth. The court’s
measured holding is correct. Under the facts of this
case, the jury could not draw the inference that the defen-
dant deliberately avoided the truth. The ostrich instruc-
tion was therefore improper. I join the opinion of the
court in that limited respect. I note that we do not hold
today that the instruction is always inappropriate in a
sting operation; indeed, our case law recognizes that, in
some circumstances, the instruction may be given in
such a situation. See United States v. Wilson, 134 F.3d
855 (7th Cir. 1998); United States v. Kaufmann, 985 F.2d
884 (7th Cir. 1993).
  With great respect for the contrary view of my col-
leagues, I do not believe that this misstep by the district
court constitutes reversible error. The evidence of the
defendant’s guilt is strong––very strong. The transcripts
of the conversations between Mr. Ciesiolka and “Ashley”
gave the jury a very firm basis for concluding that
Mr. Ciesiolka believed Ashley was a minor and never-
No. 09-2787                                                 25

theless took substantial steps to induce her to engage in
sexual activity. Moreover, unlike my colleagues, in as-
sessing the strength of the Government’s case, I am quite
comfortable in giving full weight to the circumstantial,
but nevertheless substantive, evidence of guilt sup-
plied through the operation of Rule 404(b) of the Federal
Rules of Evidence. All of this evidence was both relevant
and probative of guilt. My reading of the record leaves
me with the firm conviction, moreover, that the district
court allowed the jury to consider the Rule 404(b)
evidence only after extensive litigation of the issue and
after careful judicial consideration.1


1
  During pretrial proceedings, the Government filed a notice of
intent to use Rule 404(b) evidence at trial, see R.50, and
Mr. Ciesiolka opposed the motion, see R.68. On February 25,
2008, the district court held a hearing to consider the motion,
whereby the court scrutinized in detail the several pieces of
Rule 404(b) evidence. The parties filed additional memoranda
on the Rule 404(b) evidence issue, which the district court
duly considered. See R.56, R.57, R.68.
  Then, on February 26, 2008, before trial commenced, the
district court verbally granted the Government’s motion and
ruled that the Rule 404(b) evidence would be admitted. The
district court stated:
    [T]he Court hereby finds admissible the three types of
    evidence set forth in [the] Government’s 404(b), notice
    docket entry No. 50. The Government seeks to intro-
    duce evidence of defendant engaging in sexual conduct
    with a minor, SC, child pornography recovered from
    defendant’s computer, and additional chats recovered
                                                 (continued...)
26                                                      No. 09-2787




1
    (...continued)
       from defendant’s computer. The Court finds that all of
       this evidence is, one, directed toward establishing a
       matter and issue other than defendant’s propensity to
       commit the crime charged; two, similar enough and
       close enough in time to be relevant to the matter at
       issue; three, there is sufficient evidence to support a
       finding by the jury that the defendant committed the
       similar acts, meaning the act occurred, and that the
       defendant was the actor; and, four, the probative value
       of the evidence is not substantially outweighed by the
       danger of unfair prejudice. In this case, the similar acts
       evidence is probative of motive, intent, absence of
       mistake and knowledge, and is therefore admissible.
Tr. at 5-6, vol. I, Feb. 26, 2008.
  After trial, Mr. Ciesiolka filed a Federal Rule of Criminal
Procedure 33 motion for a new trial, whereby he challenged,
inter alia, the district court’s jury instructions concerning the
Rule 404(b) evidence. See R.83. The district court denied the
motion, providing additional explication of its ruling ad-
mitting the Rule 404(b) evidence, and making clear that
further reflection had not altered its estimation of the admissi-
bility of the evidence. See R.91 at 10. The district court stated:
      [T]his Court believes that the child pornography found
      on Ciesiolka’s computer was relevant to proving
      Ciesiolka’s knowledge that “ashley12_km” [sic] was a
      minor and absence of mistake, because it shows that
      Ciesiolka had knowledge and that he did not mistak-
      enly believe he was chatting with an adult—rather, he
      intentionally targeted an individual he believed was a
                                                    (continued...)
No. 09-2787                                                          27

  I cannot concur in my colleagues’ estimation of the
district court’s explanation of its weighing of the benefits
and burdens of admitting the Rule 404(b) evidence. More
precisely, I cannot accept that there is “an absence of any
considered explanation” of the Rule 404(b) evidence
issue. See Op. at 20. In my view, the district court’s verbal
explanation, when combined with its explanation in its
post-trial order, provides far more than an ample basis
for appellate review. In this respect, I respectfully
suggest that my colleagues give far too little weight to the
district court’s post-trial ruling. See Op. at 19-21.2


1
    (...continued)
       minor. As to the repeated rape of Jane Doe, this is also
       probative of Ciesiolka’s knowledge and absence of
       mistake. In United States v. Sebolt, 460 F.3d 910, 917 (7th
       Cir. 2006), the Seventh Circuit found that “[p]rior
       instances of sexual misconduct with a child victim
       may establish a defendant’s sexual interest in children
       and thereby serve as evidence of the defendant’s motive
       to commit a charged offense involving the sexual
       exploitation of children.” Finally, evidence of addi-
       tional Internet chats with other purported minors is
       probative of absence of mistake. It shows that Ciesiolka
       did not make a mistake in soliciting “ashley13_km,” but
       rather that he had a pattern of targeting minors over the
       Internet, and that he knowingly solicited and enticed
       “ashley13_km.”
Id.
2
  It is well-settled that a district court may explain its Rule
404(b) weighing after the Rule 404(b) evidence has been ad-
                                                  (continued...)
28                                                   No. 09-2787

  The court’s decision today is in fundamental tension
with our treatment of this issue in several recent 18 U.S.C.
§ 2422(b) cases in which, it appears, the explanations of
the trial courts in admitting Rule 404(b) evidence were
not as extensive as the one provided by the district court
here. See United States v. Zahursky, 580 F.3d 515, 523-25
(7th Cir. 2009); United States v. Hensley, 574 F.3d 384, 389
(7th Cir. 2009). As Zahursky and Hensley explain, in
§ 2422(b) cases, a transcript of the conversation soliciting
the minor is often before the jury; Rule 404(b) evidence
is particularly well-suited to prove the defendant’s
intent and motive for what he says and does during
those conversations.
  Finally, it is worth noting, indeed emphasizing, that
the district court provided a limiting instruction twice:
during the day-long presentation of the evidence and
again during the jury charge. These limiting instructions
were materially identical to the instructions we approved


2
   (...continued)
mitted. See United States v. Roe, 210 F.3d 741, 745 (7th Cir. 2000)
(“The district court’s post-trial clarifying order gives us a
sufficient basis for appellate review.”); see also United States
v. Ulland, 643 F.2d 537, 540 (8th Cir. 1981) (affirming the admis-
sion of Rule 404(b) evidence based on the district court’s
explanation of its weighing articulated in its post-trial order).
   The court’s implicit suggestion that the district court must
explain its reason for admitting Rule 404(b) evidence prior to
its admission is contrary to the case law. See Op. at 18 (citing
United States v. Macey, 8 F.3d 462, 467 (7th Cir. 1993)). Macey
does not purport to lay down any temporal rules.
No. 09-2787                                            29

in Zahursky and Hensley. We presume that     the jury fol-
lowed its instructions, and we should        continue to
treat Rule 404(b) limiting instructions as   sufficient to
eliminate any residual prejudice presented   by such evi-
dence.
  For these reasons, I would affirm the judgment of the
district court.




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