                     FOR PUBLICATION

   UNITED STATES COURT OF APPEALS
        FOR THE NINTH CIRCUIT


 UNITED STATES OF AMERICA,                         No. 15-10521
                  Plaintiff-Appellee,
                                                      D.C. No.
                      v.                           4:13-cr-01851-
                                                     JAS-BPV-1
 CHRISTOPHER JAMES PRESTON,
              Defendant-Appellant.                    OPINION



        Appeal from the United States District Court
                 for the District of Arizona
         James Alan Soto, District Judge, Presiding

              Argued and Submitted June 8, 2017
                    Pasadena, California

                     Filed October 17, 2017

   Before: Stephen Reinhardt and Alex Kozinski, Circuit
        Judges, and Terrence Berg, * District Judge.

                   Opinion by Judge Berg;
                Concurrence by Judge Kozinski



    *
      The Honorable Terrence Berg, United States District Judge for the
Eastern District of Michigan, sitting by designation.
2                 UNITED STATES V. PRESTON

                          SUMMARY **


                          Criminal Law

     The panel reversed a conviction on two counts of
aggravated sexual abuse of a child, and remanded for a new
trial.

    The panel held that the cumulative effect of the
following errors rendered the defendant’s trial
fundamentally unfair: (1) improper witness testimony that
bolstered the alleged victim’s credibility and offered opinion
on the credibility of sex abuse allegations in general;
(2) prejudicial propensity evidence in the form of the
defendant’s ex-wife’s testimony regarding a child-incest
fantasy the defendant allegedly had in 2003; and
(3) prosecutorial misconduct – namely, commenting on the
defendant’s decision not to testify, witness vouching, and
misstating the evidence in summation.

    Concurring, Judge Kozinski joined the majority opinion,
including Part III.B, because the district court erred in
admitting testimony about the defendant’s masturbation to
establish intent, where the government provided no other
rationale for introduction of this evidence. Judge Kozinski
wrote that in the event of a retrial, he does not read this
court’s ruling as precluding the government from identifying
a different basis on which to seek admission of the
testimony, such as to show that the defendant was sexually
aroused by young boys.

    **
       This summary constitutes no part of the opinion of the court. It
has been prepared by court staff for the convenience of the reader.
                UNITED STATES V. PRESTON                  3

                        COUNSEL

M. Edith Cunningham (argued), Assistant Federal Public
Defender; Jon M. Sands, Federal Public Defender; Office of
the Federal Public Defender, Tucson, Arizona; for
Defendant-Appellant.

Robert L. Miskell (argued), Chief, Appellate Section; United
States Attorney’s Office, Tucson, Arizona; for Plaintiff-
Appellee.


                        OPINION

BERG, District Judge:

    In 2015, Christopher Preston was convicted on two
counts of aggravated sexual abuse of a child. He appeals,
arguing that evidentiary errors and prosecutorial misconduct
rendered his trial fundamentally unfair. We agree. There
were a number of trial errors and, considering that evidence
of guilt was not overwhelming, their cumulative effect
prejudiced Preston. Accordingly, we REVERSE.

I. BACKGROUND

   A. Statement of Facts

    In 1998, Christopher Preston lived with his then-wife
Andrea Preston on the Tohono O’odham reservation in
Tucson, Arizona, where he worked as an electrician. Preston
befriended one of his colleagues, Sean Fox, who had three
stepsons—Timothy, Barry, and Mitchell Rosenberg. Mr.
Fox, his stepsons, and his wife Kathleen (the boys’ mother),
would occasionally visit the Prestons’ home to socialize.
4               UNITED STATES V. PRESTON

Other times, Mr. Fox went over with just the boys to strip
copper or play catch.

    That year, Preston was an assistant coach for a little
league baseball team in northwest Tucson. He arranged for
Timothy Rosenberg (“Rosenberg”)—the alleged victim in
this case, who was ten at the time—to join the team. The
fields the team practiced and played on were about an hour’s
drive from Sean Fox and Kathleen Rosenberg’s home.
Because of this logistical challenge, Rosenberg’s parents
generally did not transport him to his games or practices.
Instead, Preston did.

    Some weekends, the team played in tournaments
spanning Friday, Saturday night, and Sunday. On such
weekends, Rosenberg would stay overnight at Preston’s
home on both Friday and Saturday. Rosenberg’s brother
Barry, who was fourteen at the time, testified that these
overnights occurred on ten or more occasions. When the
1998 Little League season ended, Rosenberg stopped going
to Preston’s house. A year or two later, the Fox/Rosenberg
family moved to Kansas and lost touch with the Prestons.

    By 2012, Rosenberg was a twenty-four-year-old living
in Kansas, experiencing troubles with the law and abusing
drugs and alcohol. On March 12 that year, he was admitted
to an emergency room in Wichita for an anxiety attack.
Upon discharge from the hospital, he went to his mother’s
home. In talking with his mother, Rosenberg disclosed that
Preston had molested him in 1998. This was the first time
Rosenberg had revealed this information to anyone. Ms.
Rosenberg called the police and arranged for her son to see
her former therapist, Gail Bussart.

   Bussart treated Rosenberg from March 2012 to January
2013. During treatment, Rosenberg told Bussart that Preston
                UNITED STATES V. PRESTON                  5

sexually abused him over an eighteen-month period
beginning when he was ten. He did not, however, provide
details. Bussart stopped seeing Rosenberg on January 3,
2013, because she thought he was lying about his substance
abuse.

    From late March through late April 2013, Tohono
O’odham officers and FBI agents interviewed Rosenberg.
Unlike in his conversations with Bussart, Rosenberg
provided them with details about the alleged molestation.
Specifically, he told a Tohono O’odham officer that Preston
molested him when he was seven or eight years old and that
he clearly remembered it happening twenty times. He added
that the abuse occurred on Preston’s living-room couch and
that Preston would put his penis between Rosenberg’s legs
and direct Rosenberg to masturbate him until he ejaculated.
In addition, Rosenberg met with two FBI agents and, before
the meeting, sent them a journal that he had kept throughout
his treatment by Bussart (although, according to Rosenberg,
Bussart never read it). In the journal, Rosenberg recorded
previously unrevealed information, including that: Preston
and Rosenberg had fellated one another; Rosenberg was not
certain whether he had been anally penetrated; and
Rosenberg once saw Preston in his room watching
pornography with a bottle of lubricant.

    In October 2012, Tohono O’odham Detective Manny
Rodriguez interviewed Preston about Rosenberg’s
allegations, which Preston denied. The interview was
recorded. A few days later, FBI Special Agent Mark
Dellacroce interviewed Preston and administered a
polygraph examination to him. This interview was not
recorded. Dellacroce testified at trial that, during the
interview, Preston denied Rosenberg’s allegations, but also
stated that he “could not remember” receiving oral sex from
6               UNITED STATES V. PRESTON

Rosenberg because at that time “[Preston] was a meth
addict.”

    B. Procedural History

    On October 23, 2013 a grand jury returned an indictment
charging Preston with two counts (Counts 1 and 2) of
aggravated sexual abuse of a child, in violation of 18 U.S.C.
§ 2241(c), and two counts (Counts 3 and 4) of abusive sexual
contact of a child, in violation of 18 U.S.C. § 2244(a)(5).

     On August 10, 2015, a six-day jury trial commenced.
The only direct evidence offered at trial was Rosenberg’s
testimony. Although Preston did not testify, he presented
evidence of his denials through the testimony of the law
enforcement officials who interviewed him. At the close of
its case, the government conceded that the evidence did not
support a conviction on Count 4, which was dismissed. On
August 18, 2015, the jury found Preston guilty of Counts 1
and 2 and not guilty of Count 3. On October 26, 2015, the
district court sentenced Preston to concurrent terms of
162 months in prison on Counts 1 and 2 and imposed
concurrent terms of lifetime supervised release and special
assessments totaling $200.

    On appeal, Preston argues that the district court and the
prosecutor committed a variety of errors and that these
errors—either independently or cumulatively—deprived
him of his right to a fair trial. The testifying witnesses
relevant to his appeal include Gail Bussart (Rosenberg’s
therapist), Agent Dellacroce (the FBI agent who interviewed
Preston), Andrea Preston (Preston’s ex-wife), Timothy
Rosenberg (the alleged victim), Barry Rosenberg
(Rosenberg’s brother), and Dr. Simpson (Preston’s memory
expert).
                 UNITED STATES V. PRESTON                     7

II. STANDARD OF REVIEW

    This Court reviews challenged evidentiary rulings for
abuse of discretion, United States v. Torralba-Mendia,
784 F.3d 652, 659 (9th Cir. 2015), and, if the district court
erred, usually then asks whether the error was harmless,
United States v. Job, 851 F.3d 889, 902 (9th Cir. 2017).
Claims of prosecutorial misconduct are also generally
reviewed under the harmless error standard. United States
v. Alcantra-Castillo, 788 F.3d 1186, 1190 (9th Cir. 2015).
Where a defendant raises an issue on appeal that was not
raised before the district court, the review is for plain error.
United States v. Pelisamen, 641 F.3d 399, 404 (9th Cir.
2011).

    Where, however, as here, there are multiple trial errors,
“‘a balkanized, issue-by-issue . . . review’ is far less
effective than analyzing the overall effect of the errors in the
context of the evidence introduced at trial against the
defendant.” United States v. Frederick, 78 F.3d 1370, 181
(9th Cir. 1996) (quoting United States v. Wallace, 848 F.3d
1464, 1476 (9th Cir. 1988)). This is because the cumulative
effect of multiple trial errors “‘can violate due process even
where no single error . . . would independently warrant
reversal.’” Parle v. Runnels, 505 F.3d 922, 927 (9th Cir.
2007) (citation omitted); see also, e.g., Thomas v. Hubbard,
273 F.3d 1164, 1181 (9th Cir. 2011). In deciding whether
the combined effect of multiple errors prejudiced a
defendant we ask whether the errors stand in “‘unique
symmetry . . . , such that [they] amplify each other in relation
to a key contested issue in the case.’” Ybarra v. McDaniel,
656 F.3d 984, 1001 (9th Cir. 2011) (quoting Parle, F.3d 505
at 933).
8                UNITED STATES V. PRESTON

III.      DISCUSSION

    Preston raises over fifteen individual trial errors, across
seven different categories. We reverse based on the
cumulative effect of the following: (1) improper witness
testimony that bolstered Rosenberg’s credibility and offered
opinion on the credibility of sex abuse allegations in general;
(2) prejudicial propensity evidence in the form of Preston’s
ex-wife’s testimony regarding a child-incest fantasy Preston
allegedly had in 2003; and (3) prosecutorial misconduct,
namely: commenting on Preston’s decision not to testify,
witness vouching, and misstating the evidence in
summation. Because we find cumulative error, we do not
decide the prejudice caused by any of these individual errors,
nor do we reach the merits of the remaining errors Preston
alleges.

       A. Testimony Bolstering Rosenberg and Opining on
          Sex Abuse Generally

    The first set of trial errors we discuss arises from
testimony by Gail Bussart, Barry Rosenberg, and Agent
Dellacroce that suggested Rosenberg’s allegations of abuse
were believable or were likely to be true. This set of errors
also involves a portion of Bussart’s testimony, offered as lay
opinion, which opined on the general believability of sex
abuse allegations and on whether Rosenberg demonstrated
emotions consistent with sex abuse victims generally.

          1. Legal Standards

    Just as “[i]t is emphatically the province and duty of the
judicial department to say what the law is,” Marbury v.
Madison, 5 U.S. 137, 177 (1803), it is emphatically the
“province and duty [of the jury] to determine . . . the weight
and the credibility of the testimony of the witnesses . . . . ”
                 UNITED STATES V. PRESTON                     9

Allis v. United States, 155 U.S. 117, 121 (1894); United
States v. Bonds, 784 F.3d 582, 603 (9th Cir. 2015) (“[W]e
must respect the exclusive province of the jury to determine
the credibility of witnesses . . . .) (citation omitted).
Accordingly, “testimony regarding a witness’s credibility is
prohibited unless it is admissible as character evidence.”
United States v. Sanchez-Lima, 161 F.3d 545, 548 (9th Cir.
1998).

    Additionally, while expert witnesses may testify in the
form of opinion as to general matters based on specialized
knowledge, Fed. R. Evid. 702, lay witnesses may not. Fed.
R. Evid. 701.

       2. Gail Bussart’s Testimony

    The first portion of Bussart’s testimony alleged to be
error arises from an email that she wrote to one of her
supervisors, stating, “[I] saw [Rosenberg] on January 3,
2013, I suspected lies and dishonest behavior at that time . . .
I reinterated [sic] to [Rosenberg] the necessity of clean and
sober behavioral [sic] in order for this therapist to continue
with services.” In a written opinion overruling the
government’s objection, the district court admitted this
email, under Fed. R. Evid. 608, as Bussart’s opinion of
Rosenberg’s character for untruthfulness with respect to
drug and alcohol use. The Court added, “[t]he Government,
of course, can cross-examine the therapist on her opinion as
to whether her opinion is limited to lies about drug use or is
made more broadly.”

    Preston argues—and we agree—that there were three
instances of error related to this email during Bussart’s
testimony:
10              UNITED STATES V. PRESTON

   First, on direct examination, the government and Bussart
had the following exchange:

       “Q: [When you emailed your supervisor] that
       you thought Tim was lying to you . . . did you
       think he was lying to you about the alcohol
       and drugs or did you think he was lying to
       you about the sexual abuse?

       A: The alcohol and drug use.

       Q: Not the sexual abuse?

       A: Not the sexual abuse.”

Defense counsel objected to the government’s initial
question on the bases of foundation and speculation, but the
district court overruled the objection.

   Second, on cross-examination, defense counsel and
Bussart had the following exchange:

       “Q: [A]s far as the suspicion of lies, you just
       say, “I suspected lies, dishonest behavior at
       the time,” but you don’t specifically refer-
       ence or say about drug use?

       A: I only talked to her about his alcohol and
       drug use, nothing else [. . .]

       Q: And you can’t say for sure what else he
       has possibly lied to you about?

       A: I can say he wasn’t lying about his sexual
       abuse. It is my opinion, my professional
       opinion.
                 UNITED STATES V. PRESTON                     11

    Third, as its final question on redirect, the government
asked Bussart, “[i]s it your opinion that Tim Rosenberg was
truthful to you about the sexual abuse?” She replied, “[i]t is,
yes.”

      Shortly after this question was asked, defense counsel
objected and the district court overruled the objection,
stating that it was “tardy” and that the question was
“appropriate . . . in view of the questions that were asked in
cross.” The next day, however, the district court issued a
curative instruction to the jury regarding Bussart’s
testimony. The court stated, “You are the exclusive judges
of who to believe . . . so to the extent that Ms. Bussart offered
any opinion or belief about the truthfulness of another
witness, you must disregard that and decide for yourselves
. . . .” In its final charge to the jury, the court repeated this
instruction.

    The government does not contest that it was improper for
Bussart to indicate that she believed Rosenberg was telling
the truth about the sexual abuse allegations. Rather, the
government argues that we should not review this issue
because, in moving to admit Bussart’s email, the defense
invited any error that occurred. The government points out
that the district court’s order admitting the email “expressly
allowed the [prosecutor] to clarify the extent of [Bussart’s]
opinion.”

     The defense did not invite this error. The district court
allowed the defense to question Bussart about her opinion in
the email regarding Rosenberg’s truthfulness about drug and
alcohol use and granted the government permission to
“cross-examine [her] . . . as to whether her opinion is limited
to lies about drug use or is made more broadly.” This ruling
did not authorize the government to elicit Bussart’s
opinion—which the prosecutor did on both direct and
12                 UNITED STATES V. PRESTON

redirect—as to whether Rosenberg was telling the truth
about the ultimate issue: whether Preston sexually abused
him. 1    Although some of defense counsel’s cross-
examination may have expanded the area of inquiry (for
example, “you can’t say for sure what else he has possibly
lied to you about?”), this line of questioning was a response
to the government’s elicitation of Bussart’s statement that
she believed Rosenberg’s allegations. Defense counsel did
not invite Bussart’s three clearly improper statements
regarding her belief in the veracity of Rosenberg’s
allegations, and the district court abused its discretion by
allowing them.

    In addition to improper opinion testimony indicating that
she believed Rosenberg individually, Bussart gave improper
opinion testimony as a lay witness about whether sex abuse
victims generally tell the truth. The government never
noticed Bussart as an expert, and the district court denied the
government’s request, the day before trial, to offer expert
testimony concerning a worksheet entitled “Adult Grooming
Behaviors for Sexual Abuse of Children.” The court
instructed the government that Bussart was allowed to testify
about her treatment of Rosenberg specifically and about
grooming, but only to the extent that the topic came up
during treatment. The court did not allow her to offer an
opinion as an expert on any topic.




     1
       Based on the district court’s preliminary ruling, a proper question
for the prosecutor to ask Bussart would have been: “Is your opinion about
Rosenberg’s lack of truthfulness limited to his statements to you
concerning his use of drugs and alcohol, or are you saying he was
generally untruthful?”
                 UNITED STATES V. PRESTON                    13

    At trial, Bussart offered two opinions regarding sexual
abuse generally, and the district court erred in allowing her
to do so.

    First, although defense counsel failed to object, the
district court plainly erred in allowing Bussart to answer the
following juror question: “To the best of your knowledge,
have you treated males for sexual abuse only to find the
abuse to be false?” Bussart replied, “I have not experienced
that even when I have done—treated men and women or
girls or boys, yes, that the allegation has normally been true.”
The court should have stricken this testimony. Testifying as
a lay witness, Bussart did not offer any factual basis in
support of the assertion that all the allegations made by
people she treated had “normally been true.”

    Second, the district court abused its discretion by
permitting the following juror question over defense
counsel’s objection, which was posed by a juror to Bussart:
“Based off of your sessions with Tim and his emotions, did
his emotions demonstrate similarity to those of a person that
had been a victim of sexual abuse?” Bussart replied, “Yes.
Very much so.” The court had not qualified Bussart to offer
expert opinion concerning how sex abuse victims generally
demonstrate their emotions. To permit this question and
response was an abuse of discretion, running afoul of the
court’s instruction that Bussart could only testify about her
personal experience in treating Rosenberg.

    In sum, the district court abused its discretion in
(1) allowing the government’s line of questioning that led to
Bussart’s three improper statements indicating that she
believed Rosenberg’s allegations, and (2) permitting a
juror’s question to be asked regarding whether Rosenberg
demonstrated his emotions in a manner consistent with sex
abuse victims generally. In addition, it was plainly
14              UNITED STATES V. PRESTON

erroneous for the district court to allow Bussart to state that
allegations of sexual abuse in her patients had normally been
true. We do not decide the prejudicial effect of these errors
independently. Instead, we reserve our analysis of the
prejudicial effect of Bussart’s testimony until the end of the
opinion, where we discuss the cumulative effect of all the
errors at trial. See infra Part III.D.

       3. Barry Rosenberg’s Testimony

    The next improper opinion testimony we consider is that
offered by Barry Rosenberg, Tim Rosenberg’s brother.

    In the summer of 1998, Barry, then fourteen years old,
also frequently spent time at Preston’s home. At trial he
testified about his experiences there. Preston contends that
the following testimony—elicited in response to a juror
question—impermissibly allowed Barry to offer his opinion
that he found his brother’s allegations of sexual abuse to be
believable:

       Q: “What was your response when you
       learned about the allegations of sexual abuse
       by the defendant?”

       A: “[T]here wasn’t any questioning my
       brother about what he was saying. There was
       just understanding. I can understand. I can
       see. Things make sense to me.”

    The defense did not object to this question or to Barry’s
answer, and the issue was therefore not preserved for appeal.
Consequently, we review for plain error. The government
argues that the statement “there wasn’t any questioning my
brother about what he was saying” was ambiguous. While
that statement may be interpreted in different ways, one
                 UNITED STATES V. PRESTON                   15

reasonable way of interpreting it is that Barry found “what
[his brother] was saying” to be beyond question. In any
event, Barry’s four subsequent statements—“There was just
understanding. I can understand. I can see. Things make
sense to me”—were more definitive. In this context, the
“things” that Barry understood, saw, and made sense to him,
were his brother’s allegations that Preston sexually abused
him. Because a reasonable juror would have understood this
testimony as Barry professing his belief in the veracity of his
brother’s allegations, permitting this testimony was plain
error. Barry Rosenberg’s statements will factor into our
cumulative error analysis.

       4. Agent Dellacroce’s Testimony

    In the course of his investigation, Special Agent
Dellacroce interviewed Preston and gave him a polygraph
exam. In a pretrial ruling, the district court held that
Dellacroce could not mention the polygraph or its results but
could testify about the questions he asked Preston during the
exam, as well as Preston’s answers. During direct
examination, the government and Dellacroce had the
following exchange:

       Q: [. . .] Did you ask the defendant did you
       put your penis in [Rosenberg’s] mouth at
       your house?

       A: Yes.

       Q: And what was the defendant’s response to
       [the] question[]?

       A: No.
16                UNITED STATES V. PRESTON

        Q: Did you indicate to the defendant that you
        did not believe him?

        A. Yes.

        Q: What was the defendant’s response when
        you told him you didn’t believe him?

        A: Preston never denied receiving blow jobs
        from [Rosenberg] . . . [he] stated that he
        could not remember receiving blow jobs
        from [Rosenberg] because that is when he
        was a meth addict.”

    Preston made no objection about this testimony, and the
government, citing an unpublished disposition, argues that it
was not plain error to allow it because Dellacroce was
merely describing an interrogation technique—he told
Preston he did not believe him in order to try and elicit a
confession. The record before us does not support the
government’s position that Agent Dellacroce was testifying
to his investigative techniques—or that the jury would have
any way of knowing that. We simply have the question,
“Did you indicate to the defendant that you did not believe
him?” and the answer, “Yes”—a statement from a witness
that the defendant’s denial was not credible. Moreover, no
curative instruction was given. It was thus plainly erroneous
for the district court to allow Dellacroce to testify that he did
not believe Preston’s denial of Rosenberg’s allegations. We
will weigh Dellacroce’s statements in our cumulative error
analysis.
                UNITED STATES V. PRESTON                   17

   B. Preston’s Alleged 2003 Child-Incest Fantasy

   Preston contends that the district court erred in admitting
the testimony of his ex-wife—Andrea Preston—that in
2003, five years after Preston allegedly abused Rosenberg,
she witnessed Preston masturbating while looking at a
computer image of his eight-year-old stepson clothed in
socks and underwear.

    Before trial, defense counsel moved to exclude this
testimony as impermissible propensity evidence and the
government responded that it should be admitted under Fed.
R. Evid. 404(b) to prove Preston’s intent to molest
Rosenberg. In a written order, the trial court denied the
motion and found the evidence to be admissible under the
intent exception to Rule 404(b). At trial, as expected,
Andrea Preston testified to having witnessed the defendant
masturbating to a picture of his eight-year-old stepson some
five years after the abuse charged in the indictment allegedly
occurred. In its summation, the government reiterated her
testimony, adding that this evidence, “only goes to
[Preston’s] intent and that’s it.”

    For the reasons set forth below, we find that the district
court abused its discretion in allowing Ms. Preston’s
testimony.

       1. Legal Standards

     Rule 404 of the Federal Rules of Evidence creates a
general prohibition on using evidence of a person’s character
or character trait in order to prove that on a particular
occasion a person acted in accordance with that character or
trait. Fed. R. Evid. 404(a)(1). There is also a particular
prohibition against using evidence of other crimes, wrongs,
or acts to prove a person’s character in order to show that on
18              UNITED STATES V. PRESTON

a particular occasion the person acted in accordance with
that character. Fed. R. Evid. 404(b)(1). This same Rule,
however, carves out certain “permitted uses” of such
evidence. Specifically, evidence of other crimes, wrongs, or
acts may be admissible “for another purpose, such as proving
motive, opportunity, intent, preparation, plan, knowledge,
identity, absence of mistake, or lack of accident.” Fed. R.
Evid. 404(b)(2). Even where 404(b) evidence falls within a
permitted purpose, it should be excluded, under Rule 403, if
the court finds that its probative value is substantially
outweighed by a danger of unfair prejudice. Fed. R. Evid.
403.

    This case involves evidence of an “other act” that
occurred some five years after the events charged in the
indictment. We have held that evidence of a subsequent act
may be admitted under 404(b). United States v. Lloyd,
807 F.3d 1128 (9th Cir. 2015). But in introducing other act
evidence, the government always must show: (1) that the act
tends to prove a material element or point, (2) that the act is
not too remote in time from the crime charged, and (3) that
the evidence is sufficient to support a finding that the
defendant committed the subsequent act. Id.

    When seeking to introduce other act 404(b) evidence for
the purpose of proving intent, the proposing party must show
that the other “act is similar to the offense charged.” United
States v. Hadley, 918 F.2d 848, 851 (9th Cir. 1990)
(evidence of prior isolation and sodomy of students
sufficiently similar to charged crime of isolation and sodomy
of a student); see also, e.g., United States v. Vo, 413 F.3d
1010, 1018–19 (9th Cir. 2005) (prior conviction for cocaine
trafficking sufficiently similar to charged crime of
methamphetamine distribution); United States v. Ayers,
924 F.2d 1468, 1474 (9th Cir. 1991) (prior purchase of
                 UNITED STATES V. PRESTON                    19

numerous cashier’s checks, for amounts that did not trigger
banks’ duty to report them to the Internal Revenue Service,
sufficiently similar to charged crime of tax evasion). This
showing of similarity is necessary because if the other act is
not sufficiently similar to the crime charged, “it does not tell
the jury anything about what the defendant intended . . .
unless, of course, one argues (impermissibly) that the [other]
act establishes that the defendant has criminal propensities.”
United States v. Miller, 874 F.2d 1255, 1269 (9th Cir. 1989).

       2. Analysis

    In a written Order admitting Ms. Preston’s testimony
about the 2003 masturbation incident, the district court held
in relevant part:

       “Evidence that the Defendant was sexually
       interested in a young boy approximately the
       same age the victim was at the time of the
       charged events could make it more likely that
       the Defendant had the intent to commit
       sexual acts in this case or that such acts were
       not a mistake. The evidence is, therefore,
       relevant. The similarity between the victim’s
       age at the time of the charged acts and the age
       of the boy in the image creates a high
       probative value for that evidence, and it is not
       substantially outweighed by any prejudice
       caused to the Defendant.

       Finally, the evidence is sufficiently similar
       under Rule 404(b) to show the Defendant’s
       intent because of the similarity in the age of
       the victim and boy in the image;
       approximately five years subsequent is not
       too remote in time, see United States v.
20               UNITED STATES V. PRESTON

       Johnson, 132 F.3d 1279, 1283 (9th Cir.
       1997); eyewitness testimony from the
       Defendant’s ex-wife is sufficient to introduce
       the evidence to the jury; and, the evidence is
       probative of the Defendant’s intent to engage
       in sexual conduct, an essential element of at
       least one charged act.”

    On appeal, Preston argues that the subsequent act was
not sufficiently similar to the crime charged to be properly
admitted via 404(b) under an intent theory of admissibility.
Moreover, Preston contends that the district court should
have excluded the evidence under Rule 403, because intent
was not in dispute in this case and therefore any marginal
probative value of this evidence was substantially
outweighed by the danger that the jury would draw a
propensity inference against Preston on the basis of his ex-
wife’s highly prejudicial testimony.

    We agree with Preston. In admitting Andrea Preston’s
testimony, the district court abused its discretion in two
ways. First, under Hadley, the district court must find that
the “other act” sought to be introduced under 404(b) to prove
intent is similar to the crime charged. Here, the district court
found only that the age of Preston’s stepson in the
photograph to which Preston masturbated (8 years old) was
similar to Rosenberg’s age when Preston allegedly molested
him (10 years old). This finding does not adequately explain
or discuss how the act of masturbating to a picture of a boy
in underwear—a non-criminal act—is similar to the crime of
real-life sexual abuse of a child. The district court therefore
abused its discretion in admitting Ms. Preston’s testimony
without complying with Rule 404(b)’s similarity
requirement expressed in Hadley and other cases.
                   UNITED STATES V. PRESTON                          21

    Second, the district court abused its discretion by finding
the evidence admissible under Rule 403. Rule 403 is meant
to “ensure that potentially devastating evidence of little
probative value will not reach the jury.” United States v.
Lemay, 260 F.3d 1018, 1026 (9th Cir. 2001). We have long
held that “[w]here the evidence is of very slight (if any)
probative value, it’s an abuse of discretion to admit it if
there’s even a modest likelihood of unfair prejudice or a
small risk of misleading the jury.” United States v. Wiggan,
700 F.3d 1204, 1213 (9th Cir. 2012) (quoting United States
v. Hitt, 981 F.2d 422, 424 (9th Cir.1992)).

    Evidence of a subsequent masturbation incident linked
to child-incest fantasy is highly prejudicial to a defendant
charged with child molestation; a jury confronted with such
disgusting evidence is likely to conclude that the defendant
“is the type” to molest a child. See United States v. Curtin,
489 F.3d 935, 964 (9th Cir. 2007) (Kleinfeld, J. concurring)
(“incest has had a rare power to disgust” (quoting Richard
A. Posner, Sex and Reason 201 (1994)). Moreover, as this
Court has recognized, in many cases, the “link between
fantasy and intent is too tenuous to be probative,” as
“[p]eople commonly fantasize about doing things they have
no intention of actually doing.” 2 And fantasy is even less
probative of intent in cases where, as here, intent is not
actually disputed—that is, where the defense is a general
denial of committing the offense, rather than an admission
to an act coupled with a specific denial of the requisite intent.
When the defendant generally denies committing the offense

    2
      Where the other acts offered are specific incidents of prior child
molestation—which would clearly be similar to the charged offense
here—Federal Rule of Evidence 414 expressly permits them to be
admitted “on any matter to which it is relevant.” Other acts of mere
fantasy or auto-eroticism, however, are not permitted under this rule.
22                  UNITED STATES V. PRESTON

of sexual abuse, the victim’s testimony that the abuse
occurred—if accepted by the jury—effectively proves all of
the elements of the offense, including that the defendant
intended to seek sexual gratification. In such circumstances,
proof of another act showing a defendant’s sexual
proclivities toward children contributes little to the
government’s case. It just tempts the jury to draw the
impermissible inference that the defendant has a propensity
to sexually abuse children. 3

     Here, the “visceral impact” of this evidence “far exceeds
[its] probative value.” See Hitt, 921 F.2d at 424 (finding that
mere “photographs of firearms often have a visceral impact
that far exceeds their probative value”). Because Preston’s
alleged 2003 incest fantasy had little probative value (abuse
and fantasy are dissimilar acts, and Preston did not put intent
at issue in the case), and great potential to inspire prejudice
(incest is a uniquely disgusting act, and juries are apt to draw
a propensity inference from other act evidence), the district
court abused its discretion in admitting it.

    In sum, the district court abused its discretion in
(1) admitting Andrea Preston’s testimony under Rule 404(b)

     3
      This scenario stands in contrast to sexual misconduct cases where
a defendant puts intent at issue and other act evidence of their deviant
fantasies, therefore, increases in probative value. See, e.g., Curtin,
489 F.3d at 950 (child-sex stories in defendant’s possession probative of
intent where he was charged with attempting to engage in a sexual act
with a minor and admitted to talking to an individual online who
identified as a minor but testified that he intended her to be an adult
roleplaying a teen); United States v. Cunningham, 607 F. App’x. 715
(9th Cir. 2015) (child pornography that the defendant downloaded
probative of intent where he was charged with intending to use a child to
produce a sexually explicit visual depiction and admitted taking pictures
of a child but testified that he did not intend for any of the pictures to be
pornographic).
                 UNITED STATES V. PRESTON                     23

without first establishing how Preston’s masturbation
fantasy was similar to sexually abusing Rosenberg, and
(2) admitting the evidence under Rule 403 given its slight
probative value and high risk of unfair prejudice. We will
analyze this prejudicial effect within our cumulative error
analysis.

    C. Prosecutorial Misconduct

    The next set of alleged trial errors relates to prosecutorial
misconduct. Specifically, Preston argues that the prosecutor
improperly commented on Preston’s decision not to testify,
impermissibly vouched for Rosenberg, and misstated the
evidence in summation.

        1. Commenting on Preston’s Failure to Testify

     To realize the Fifth Amendment’s guarantee against
compelled self-incrimination, the Supreme Court has held
that it is improper for a prosecutor to comment on a
defendant’s decision not to testify. Griffin v. California,
380 U.S. 609, 615 (1965). The government may comment
on the defense’s argument, but may not make a comment “‘if
it is manifestly intended to call attention to the defendant’s
failure to testify, or is of such a character that the jury would
naturally and necessarily take it to be a comment on the
failure to testify.’” Rhoades v. Henry, 598 F.3d 495, 510 (9th
Cir. 2010) (quoting Lincoln v. Sunn, 807 F.2d 805, 809) (9th
Cir. 1987)). Thus, where a defendant is the only possible
witness who could rebut the testimony of the government
witnesses, it is inappropriate for a prosecutor to point out the
lack of witnesses or testimony on the other side, because
“‘this can only cause the jury to naturally look to the only
other evidence there is—the defendant—and, hence, this
could be a prohibited comment on the defendant’s failure to
24                UNITED STATES V. PRESTON

testify.’” Lincoln at 809 (quoting United States v. Cianciulli,
482 F. Supp. 585, 591–92 (E.D. Pa. 1979)).

    Preston argues that the prosecutor impermissibly
commented on his failure to testify when the government
stated in summation, “[Rosenberg] was sexually abused. He
told you under oath on the stand. There’s no evidence,
there’s no testimony in this case that contradicts Tim
Rosenberg’s testimony.”

    Here, although the prosecutor did not mention Preston
by name, the government’s comment was impermissible
under Lincoln because it directed the jury’s attention to a
lack of testimony contradicting Rosenberg. The only person
who could have provided testimony to contradict
Rosenberg’s version of the events was Preston, since the
only other two persons present in the home at the time the
abuse allegedly occurred—Barry Rosenberg and Andrea
Preston—testified that they never suspected anything. In
this context, it was plain error for the prosecutor to state that
“there’s no testimony in this case that contradicts Tim
Rosenberg’s testimony,” because the jury would have
immediately inferred that they did not hear testimony from
Preston, the only witness who could have directly
contradicted Rosenberg’s allegations. 4 We reserve an
analysis of the prejudicial effect of the prosecutor’s
comment for our cumulative error analysis.




     4
      Moreover, the prosecutor’s statement that there was no evidence
contradicting Rosenberg’s testimony was, strictly speaking, incorrect:
both Agent Dellacroce and Detective Rodriguez testified that, during
their respective interviews of Preston, he denied Rosenberg’s
allegations.
                UNITED STATES V. PRESTON                 25

       2. Vouching for Rosenberg

    Preston further argues that the government
impermissibly vouched for the veracity of Rosenberg’s
testimony. “Improper vouching consists of placing the
prestige of the government behind a witness through
personal assurances of the witness’s veracity, or suggesting
that information not presented to the jury supports the
witness’s testimony.” United States v. Ruiz, 710 F.3d 1077,
1085 (9th Cir. 2013) (citation omitted).

    Preston contends that the government offered personal
assurances of Rosenberg’s veracity in the following
instances:

       1. In opening, the government stated, “The
       truth always comes out no matter how many
       years have passed . . . And the truth in this
       case is that the defendant, Christopher
       Preston, put his penis in ten-year-old
       Timothy Rosenberg’s mouth . . . .”

       2. In summation, the government reiterated,
       “The truth will always come out . . . . And in
       this case the truth has come out.” The
       government further noted, “In the end . . .
       ladies and gentlemen, the truth came out of
       the mouth of Tim Rosenberg.”

       3. In rebuttal, referring to Rosenberg’s
       testimony, the government stated, “And that
       is the truth in this case. That is the evidence
       in this case.”        Later in rebuttal, the
       government added, “[Rosenberg] has come
       here to court . . . to testify to you as to the
       truth of what happened . . . the
26              UNITED STATES V. PRESTON

       uncontroverted truth as to what happened.”
       The government also stated, “the crux of this
       case, the core of the truth of what Timothy
       Rosenberg testified to in detail on the stand
       under oath is that the defendant sexually
       molested him as a child. . . .” Finally, the
       government declared, “[Rosenberg] probably
       wishes that the drinking and the drugs . . .
       could erase this memory of what happened.
       But it can’t. And it didn’t. Because it is the
       truth of what happened.”

    The defense objected only to the final comment.
Although the court overruled the objection, the government
did remind the jury that “what attorneys argue to you
obviously is not evidence” and stated “we are not vouching
for [Rosenberg] . . . what the government is saying is this is
what the evidence shows, this is what the testimony shows,
this is what—Tim’s testimony has been corroborated.”

    In United States v. Weatherspoon, we held that the
government improperly vouched for its witness where the
prosecutor stated “three times over in rapid succession that a
witness ‘told the truth.’” 410 F.3d 1142, 1148 (9th Cir. 2005)
(noting that the “ethical bar is set higher for the prosecutor
than for the criminal defense lawyer”). In this case, the
prosecutor stated at least three times that Rosenberg told the
truth or that his allegations were true ((1) “the truth in this
case is that [Preston] put his penis in [Rosenberg’s mouth];”
(2) “In the end . . . the truth came out of the mouth of
[Rosenberg]; and (3) “Rosenberg probably wishes that the
[drugs] could erase this memory . . . But they can’t . . .
Because this is the truth of what happened.”). As in
Weatherspoon, this amounted to improper vouching. The
district court abused its discretion in allowing the final
                 UNITED STATES V. PRESTON                     27

comment over defense counsel’s objection. Accordingly,
these statements will factor into our cumulative error
analysis.

        3. Misstatement of the Evidence

    Finally, Preston argues that the government misstated
the evidence in summation. A prosecuting attorney may not
misstate or manipulate the evidence at trial. Darden v.
Wainwright, 477 U.S. 168, 182 (1986); United States v.
Kojayan, 8 F.3d 1315, 1320–22 (9th Cir. 1993).

    During summation and again in rebuttal, government
counsel stated to the jury, without objection, that the defense
was asking them to believe that Rosenberg is “making up
these allegations because he is a vicious, cold, calculating
human being,” and that “the only two possibilities in this
case are that Rosenberg is telling the truth,” or that he “is
truly despicable and evil and lying about everything for no
reason.” This argument misstates the evidence. The defense
presented no evidence suggesting that Rosenberg was a
“vicious” or “evil” liar, nor was this line of attack part of any
argument advanced by the defense. Instead, the defense
simply provided expert opinion testimony that Rosenberg
may have experienced memory problems as a consequence
of his drug use. The defense’s memory expert, Dr. Simpson,
testified that individuals, and especially drug addicts, can
make “source monitoring errors,” whereby they confuse an
imagined, dreamed, or hallucinated event with one that
actually occurred. The prosecutor posed a false choice to the
jury (that either what Rosenberg is saying is the truth, or else
he is an evil liar). The government also misstated the nature
of the evidence (which was actually that Rosenberg could be
misremembering or could be telling the truth). It was plainly
improper for the prosecutor to characterize the evidence in
28              UNITED STATES V. PRESTON

this manner, and the government’s statements will be
factored into our cumulative error analysis.

     D. Cumulative Error Analysis

     Having identified the trial errors in this case, we turn
now to a discussion of whether their cumulative effect
prejudiced Preston. Below is a summary of the errors at
trial—including a description of any mitigating or
aggravating factors (such as a curative instruction or a jury
question indicating that a juror did not follow a curative
instruction)—followed by an analysis of these errors within
the context of the trial and in view of the strength of the
government’s case.

        1. Trial Errors

    The first series of errors relates to the opinion testimony
that bolstered the veracity of Rosenberg’s testimony.
Bussart stated on three separate occasions that she believed
Rosenberg’s allegations were true; Barry Rosenberg
testified that he did not question his brother’s allegations
because they made sense to him; and Agent Dellacroce
testified that he did not believe Preston when he denied
Rosenberg’s allegations. In addition, Bussart impermissibly
offered her opinion that victims’ sexual abuse allegations are
generally true and that Rosenberg’s emotions were similar
to those of a person who has suffered sexual abuse.

    The court did give a curative instruction following
Bussart’s testimony, explaining to the jury that they must
disregard any witness’s opinion about the truthfulness of
another witness. However, after Agent Dellacroce testified
that he did not believe Preston’s denial two separate jurors
sought to ask Agent Dellacroce—who testified after
Bussart—why he did not believe Preston. This suggests that
                UNITED STATES V. PRESTON                    29

the jurors focused on Dellacroce’s opinion that Preston was
not believable, and that they had trouble absorbing the
court’s earlier instruction to disregard witness testimony
about the truthfulness of others. See Avila v. Los Angeles
Police Dept., 758 F.3d 1096, 1118 n.17 (9th Cir. 2014)
(Vinson, J., dissenting) (jury questions can serve as evidence
of the effectiveness of curative instructions).

    Next, the trial court erred in allowing Ms. Preston to
testify that in 2003 she saw Preston masturbating to a picture
of his eight-year-old stepson in socks and underwear. In
summation, the government reiterated her testimony and
added that this evidence, “only goes to [Preston’s] intent and
that’s it.”

     Finally, the errors included the following conduct by the
prosecutor: (1) commenting on Preston’s decision not to
testify, (2) asserting at least three times that Rosenberg was
telling the truth (which the prosecutor tried to mitigate after
the fact, by reminding the jury that what attorneys argue is
not evidence), and (3) suggesting inaccurately that the
evidence presented a choice between either believing
Rosenberg and finding Preston guilty, or necessarily finding
that Rosenberg was a diabolical liar and that Preston was not
guilty.

       2. Cumulative Effect

    The government correctly highlighted the key issue in
this case in its summation to the jury by stating that, “[i]n
this case really there’s only one question: do you believe Tim
Rosenberg or not?” The cumulative effect of these trial
errors prejudiced Preston because almost all of them
implicated this very question. Because this cumulative effect
is so clear, we do not decide the individual prejudice of any
of the errors.
30               UNITED STATES V. PRESTON

     Three of the errors involve statements—by Bussart,
Barry Rosenberg, and the prosecutor—either asserting or
implying that Tim Rosenberg’s testimony was true. Two
others, Agent Dellacroce’s testimony and the prosecutor’s
comment on Preston’s decision not to testify, improperly
suggested the inverse—that Preston’s denial of the
allegations was false. Moreover, the prosecutor suggested
that the jury could only find Preston not guilty by deciding
that Tim Rosenberg—for whom the government and many
of their witnesses had vouched—was a diabolical liar. In
this way, the errors at trial were not isolated. Indeed, they
stand in “unique symmetry such that they amplify each other
in relation to [the] key,” and only, “contested issue in the
case”—whether the alleged victim, Tim Rosenberg, was
telling the truth. Ybarra v. McDaniel, 656 F.3d 984, 1001
(9th Cir. 2011) (quoting Parle v. Runnels, 505 F.3d 922, 933
(9th Cir. 2007)).

    The only error in this case that did not relate to bolstering
Rosenberg as a truth-teller was hardly insignificant. Andrea
Preston’s testimony about Preston’s masturbation suggested
he had the character of a child molester. Where intent was
not in dispute, allowing such inflammatory evidence likely
had a prejudicial effect by encouraging the jury to believe
that Preston was the type of person who would sexually
abuse Rosenberg.

    Moreover, the government’s case hinged almost entirely
on Rosenberg’s testimony. The government points out that
Preston’s denials of the allegations were not credible
because he told Agent Dellacroce that he “could not
remember” whether he received oral sex from Rosenberg.
But Agent Dellacroce equivocated on this point and the
interview was not recorded. The only other witnesses
present in the Preston home when the molestation allegedly
                UNITED STATES V. PRESTON                    31

took place, Barry Rosenberg and Andrea Preston, testified
that they never suspected anything. Thus, the only
substantial proof that the government offered at trial was
Rosenberg’s testimony.

    In sum, there were multiple errors in the trial that
unfairly bolstered the victim’s credibility, and an additional
error that portrayed the defendant as the “type of person”
who would molest a child. In addition, the government’s
case hinged entirely on Rosenberg’s credibility, with little
additional proof to corroborate his allegations. The
cumulative effect of these errors rendered Preston’s trial
fundamentally unfair, and his conviction must therefore be
reversed and the case remanded for a new trial.

IV.    Conclusion

   For the foregoing reasons, the matter is REVERSED
AND REMANDED FOR PROCEEDINGS NOT
INCONSISTENT WITH THIS OPINION.



KOZINSKI, Circuit Judge, concurring:

    I join the majority opinion, including Part III.B, because
the district court erred in admitting the testimony about
Preston’s masturbation to establish intent. The government
provided no other rationale when seeking to introduce this
evidence at trial. In the event of a retrial, I do not read our
ruling as precluding the government from identifying a
different basis on which to seek admission of the testimony,
such as to show that Preston was sexually aroused by young
boys.
