                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,               
                Plaintiff-Appellee,            06-10145
               v.                              D.C. No.
LAWRENCE COHEN,                             CR-04-00119-KJD
             Defendant-Appellant.
                                        

UNITED STATES OF AMERICA,               
                  Plaintiff-Appellee,         No. 06-10199
                 v.                            D.C. No.
IRWIN A. SCHIFF,                            CR-04-00119-KJD
             Defendant-Appellant.
                                        

UNITED STATES OF AMERICA,                    No. 06-10201
                Plaintiff-Appellee,
               v.                              D.C. No.
                                            CR-04-00119-KJD
CYNTHIA NEUN,
                                               OPINION
             Defendant-Appellant.
                                        
        Appeal from the United States District Court
                 for the District of Nevada
         Kent J. Dawson, District Judge, Presiding

                 Argued and Submitted
       November 5, 2007—San Francisco, California

                  Filed December 26, 2007
                            16705
16706            UNITED STATES v. COHEN
    Before: Sidney R. Thomas, Richard C. Tallman, and
              Sandra S. Ikuta, Circuit Judges.

               Opinion by Judge Tallman
                       UNITED STATES v. COHEN                       16709
                              COUNSEL

Chad A. Bowers (argued), Las Vegas, Nevada, for appellant
Lawrence Cohen.

Michael V. Cristalli (argued), Las Vegas, Nevada, for appel-
lant Cynthia Neun.

Sheldon R. Waxman (argued), South Haven, Michigan, for
appellant Irwin Schiff.

Mark Determan (argued), United States Department of Jus-
tice, Tax Division, Washington, D.C., for the appellee.


                              OPINION

TALLMAN, Circuit Judge:

   These consolidated appeals follow the convictions and sen-
tences of a well-known recidivist tax protestor, Irwin Schiff,
and two of his acolytes, Cynthia Neun and Lawrence Cohen.
After Schiff’s last release from prison in 1991 for income tax
evasion, he opened a store in Las Vegas, Nevada, where he
sold books, audio tapes, videos and instructional packages,
many created by him, explaining how to “legally stop paying
income taxes.”1 Cohen and Neun worked at the store, and,
together with Schiff, they provided “consultation services” to
clients who wished to avoid paying federal income taxes.
They encouraged their clients to file “zero returns,” federal
individual income tax returns containing a zero on every line
related to income and expenses, and, in most cases, seeking
  1
   In United States v. Schiff, 379 F.3d 621, 630 (9th Cir. 2004), we upheld
a preliminary injunction on the sale of a book authored by Schiff, The
Federal Mafia: How the Government Illegally Imposes and Unlawfully
Collects Income Taxes, finding that it constituted fraudulent commercial
speech.
16710                   UNITED STATES v. COHEN
an improper refund of all federal income taxes withheld dur-
ing the tax year for which it was filed.

   Following a twenty-three day joint trial in which Schiff
represented himself, the jury returned guilty verdicts with
respect to many of the counts in the indictment. In particular,
Cohen was convicted of one count of aiding and assisting in
the filing of a false federal income tax return in violation of
26 U.S.C. § 7206(2), for which he received a thirty-three
month sentence.2 At trial, the district court summarily con-
victed Schiff of fifteen counts of criminal contempt pursuant
to 18 U.S.C. § 4013 based on his unruly courtroom behavior.
Schiff’s total sentence for those convictions was twelve
months in prison to be served consecutively to his tax evasion
and conspiracy sentence.

  Cohen argues that his conviction must be overturned
because the district court wrongfully excluded the expert testi-
mony of his psychiatrist who would have offered evidence of
   2
     Schiff was convicted of conspiracy to defraud the government for the
purpose of impeding and impairing the Internal Revenue Service in viola-
tion of 18 U.S.C. § 371 (also known as a “Klein conspiracy”; see United
States v. Klein, 247 F.2d 908 (2d Cir. 1957)); five counts of aiding and
assisting in the filing of false federal income tax returns in violation of 26
U.S.C. § 7206(2) (“aiding and assisting”), one count of tax evasion in vio-
lation of 26 U.S.C. § 7201, and six counts of filing false income tax
returns in violation of 26 U.S.C. § 7206(1). Neun was convicted of one
count of conspiracy, nine counts of aiding and assisting, three counts of
willfully failing to file income tax returns in violation of 26 U.S.C. § 7203,
one count of social security disability fraud in violation of 42 U.S.C.
§ 408(a)(3), and one count of theft of government property in violation of
18 U.S.C. § 641. In an accompanying memorandum disposition filed con-
temporaneously with this opinion, we affirm Schiff’s convictions and his
resulting 151-month sentence. We also affirm Neun’s convictions. She
does not challenge her sentence on appeal.
   3
     18 U.S.C. § 401 states, in relevant part, “A court of the United States
shall have power to punish by fine or imprisonment, or both, at its discre-
tion, such contempt of its authority, and none other, as — (1) Misbehavior
of any person in its presence or so near thereto as to obstruct the adminis-
tration of justice . . . .”
                     UNITED STATES v. COHEN                 16711
Cohen’s mental state. We agree, and we reverse Cohen’s con-
viction, vacate his sentence, and remand for a new trial.

   Schiff challenges the contempt convictions and the result-
ing sentences. We vacate the contempt convictions due to the
district court’s failure to properly file contempt orders for
each of those convictions as required by Federal Rule of
Criminal Procedure 42(b) and our precedent. We remand to
allow the district court to file those orders in proper form, to
then reinstate the contempt convictions and reimpose punish-
ment for Schiff’s contumacious behavior.

                                 I

                                A

   Schiff’s convictions for criminal contempt arose primarily
from his refusal to heed repeated warnings by the trial judge
to cease arguing to the jury his erroneous views of the law.
Schiff often instructed witnesses to read passages from his
books explaining his characterization of the voluntary nature
of the federal income tax. For example, one witness read,
“There is no question that it is . . . all correct. Paying and fil-
ing income tax[ ] are, by law, voluntary.” Schiff frequently
couched misstatements of the law in questions to witnesses.
For example, Schiff asked one witness, “Were you aware that
none of those sections [of the Internal Revenue Code] said
you . . . were required to file a tax return?” On another occa-
sion, Schiff asked a witness whether she was aware that
“there’s no provision in the law that allows the IRS to put on
liens[.]” Schiff also asked a witness whether a passage from
one of Schiff’s books “tr[ies] to establish the fact that income
in the ordinary sense is not exactly income in the tax sense.”
Schiff’s defiance also took the form of his persistent refusal
to cease particular lines of questioning after the district judge
had previously ruled them improper and misleading.

  During the first eight days of trial, the district judge dealt
with Schiff’s misconduct by sustaining the government’s
16712                UNITED STATES v. COHEN
objections and sometimes explaining to Schiff the legal basis
for doing so. Schiff nonetheless persisted. On the ninth day of
trial, following yet another transgression, the district judge
warned Schiff at a sidebar conference that if his insolence
continued, he would risk a contempt citation and sanctions.

   Schiff still did not heed the warnings. The next day, Schiff
suggested to the jury during his questioning of a witness that
the law does not prohibit the concealment of one’s assets from
the government. He also improperly suggested that the gov-
ernment lacked the power to investigate criminal violations of
the Internal Revenue Code. He continued to ask similar ques-
tions even after two objections by the government were prop-
erly sustained.

   At that point, the understandably exasperated district judge
summarily held Schiff in criminal contempt and sentenced
him to one day in jail, “deferred until the conclusion of this
trial. The next time it will double and it will continue to dou-
ble until you . . . respect the rulings of the Court.” Despite fair
warning as to the consequences of persisting in this manner,
Schiff’s contumacious behavior continued, and he was there-
after sanctioned fourteen more times during the trial. On each
of these occasions, the district judge simply stated “sanctions”
so as not to “let the sanctions overly influence the jury.”

  At Schiff’s post-trial sentencing hearing, the district judge
reduced the sentence for ten of the fifteen sanctions to one
month each:

    So, on the first sanction, it was one day; on the sec-
    ond sanction, it was two days; on the third, four
    days; on the fourth, eight days; on the fifth, sixteen
    days for a total of approximately one month cumula-
    tively as of sanction number five.

    Thereafter, what I have decided to do is impose one
    month for each successive sanction resulting in a
                       UNITED STATES v. COHEN                      16713
      total of twelve months as the sentence for contempt
      citations during trial.4

The district court briefly explained on the record its reasons
for remitting this sentence, but did not file contempt orders
for any of the convictions. Schiff was not afforded the oppor-
tunity to address the court with respect to his contempt con-
victions. Nor does it appear from the record that the court
notified Schiff in advance of the sentencing hearing that his
contempt convictions would be addressed.

                                    B

   Schiff raises three challenges to his contempt convictions
and sentence. First, he argues that the district court erred by
failing to file contempt orders as required by Federal Rule of
Criminal Procedure 42(b). Second, he asserts that the sentence
violates his right to due process under the Fifth Amendment
because he did not receive notice or an opportunity to be
heard at the post-trial sentencing hearing. Third, he maintains
that the sentence violated his Sixth Amendment right to a trial
by jury because his sentence exceeded six months. We
address each of these arguments in turn.

                                    1

   We review summary contempt convictions for abuse of dis-
cretion. United States v. Flynt, 756 F.2d 1352, 1362 (9th Cir.),
modified, 764 F.2d 675 (9th Cir. 1985). Federal Rule of Crim-
inal Procedure 42(b) authorizes a district court to “summarily
punish a person who commits criminal contempt in its pres-
  4
    The district court made a mathematical error in calculating Schiff’s
punishment for criminal contempt. If the combined punishment for the
first five contempt convictions totals thirty one days (1 + 2 + 4 + 8 + 16
= 31), and the punishment for the remaining ten convictions are each one
month, then the total punishment is eleven months, not twelve. We will
discuss the implications of this error below.
16714               UNITED STATES v. COHEN
ence if the judge saw or heard the contemptuous conduct and
so certifies . . . . The contempt order must recite the facts, be
signed by the judge, and be filed with the clerk.” (emphasis
added).

   Here, the district court did not file the requisite contempt
orders. The government argues that we should excuse the
oversight because the district court “made the reasons for the
sanctions abundantly clear on the record.” The government
relies on United States v. Marshall, 451 F.2d 372, 377 (9th
Cir. 1971), for the proposition that the “[t]he function of the
certificate [of contempt] is not to give notice to the defendant
or to frame an issue to be tried, but solely to permit an appel-
late court to review the judge’s action.” In the government’s
view, where, as here, the district court enunciates on the
record the basis for the summary contempt conviction, a sepa-
rate certificate is not required.

   [1] The government is mistaken. Our case law establishes
that the district judge must file a contempt order setting forth
in detail the factual basis of the contempt conviction and certi-
fying that the district judge personally witnessed the conduct
giving rise to the conviction. See id. at 374-75 (emphasizing
that contempt orders are “ ‘more than a formality,’ ” and find-
ing the contempt orders at issue insufficient because they con-
tained “[c]onclusory language and general citations to the
record”); see, e.g., In re Contempt of Greenberg, 849 F.2d
1251, 1254 (9th Cir. 1988) (rejecting the government’s argu-
ment that the district judge’s failure to certify that he “ ‘saw
or heard’ ” the conduct giving rise to the contempt conviction
could be cured by looking to the trial transcript and inferring
that the court must have seen or heard the conduct). The gov-
ernment’s recommendation that we forgive the district court’s
failure to issue contempt orders and accept oral findings as a
substitute runs contrary to the explicit language of Rule 42(b)
as well as every case of which we are aware to have consid-
ered this issue. See United States v. Robinson, 922 F.2d 1531,
1534-35 (11th Cir. 1991) (holding that a contempt order must
                    UNITED STATES v. COHEN                 16715
set forth the specific facts giving rise to the contempt); United
States v. Schrimsher, 493 F.2d 842, 845 (5th Cir. 1974)
(same); Pietsch v. President of U.S., 434 F.2d 861, 863 (2d
Cir. 1970) (same); Tauber v. Gordon, 350 F.2d 843, 845 (3d
Cir. 1965) (same).

   [2] We see no choice under our precedent interpreting Rule
42(b) but to vacate Schiff’s criminal contempt convictions
and remand to allow the district court to comply with the rule.
In doing so, we understand the difficulty posed by an irascible
pro se defendant like Schiff who presents himself in such a
challenging manner to a trial judge who is earnestly attempt-
ing to maintain a fair and impartial trial through order and
decorum in the courtroom. We remand to the district court to
allow it to file the requisite fifteen contempt orders. See Mar-
shall, 451 F.2d at 378; United States v. Mars, 551 F.2d 711,
715 (6th Cir. 1977); United States v. Vano (In re Herbert
Shafer), 496 F.2d 1195, 1196 (5th Cir. 1974). On remand, the
district court may reinstate the contempt convictions and
resentence him so long as it does not increase the individual
punishments for any of the fifteen convictions. As discussed
in footnote four, the district court made a mathematical error
in computing Schiff’s sentence, and using the district court’s
logic as to how the sentence was calculated, the correct sen-
tence in total is not more than eleven months. The district
court retains the discretion to impose the contempt sentence
consecutively to Schiff’s other sentences should it again
choose to do so.

                               2

   Next, we address Schiff’s argument that his sentences for
the contempt convictions were imposed in violation of his
Fifth Amendment right to due process and Sixth Amendment
right to a jury trial. The contours of Schiff’s argument are less
than clear. He seems to be arguing that, in effect, he was not
summarily convicted and punished for criminal contempt fif-
teen times during trial, but rather, was cited fifteen times dur-
16716               UNITED STATES v. COHEN
ing trial and, at the post-trial sentencing hearing, was given a
single sentence exceeding six months.

   In Schiff’s view, where a person is cited for criminal con-
tempt during trial but punished after, that person is entitled
under the Fifth Amendment’s Due Process Clause to notice
and an opportunity to be heard at the sentencing hearing.
Schiff also contends that where a person is given a single pun-
ishment for multiple acts of contempt, that person is entitled
under the Sixth Amendment to a jury trial if the punishment
exceeds six months. We do not disagree with those general
legal propositions. See Taylor v. Hayes, 418 U.S. 488, 498-99
(1974) (holding that an attorney, who was cited for contempt
during trial but was sentenced after the trial, was entitled to
“reasonable notice of the specific charges and opportunity to
be heard in his own behalf”) (citing Groppi v. Leslie, 404 U.S.
496, 506 (1972)); Int’l Union, United Mine Workers of Am.
v. Bagwell, 512 U.S. 821, 832 (1994) (“If a court delays pun-
ishing a direct contempt until the completion of trial, . . . due
process requires that the contemnor’s rights to notice and a
hearing be respected.”) (citing Taylor, 418 U.S. at 498);
Codispoti v. Pennsylvania, 418 U.S. 506, 517 (1974) (holding
that the appellants were entitled to a jury trial where they
were cited multiple times for criminal contempt during the
trial, and given a sentence after the trial in excess of six
months).

   [3] However, we reject Schiff’s premise based on his con-
tention that he was cited during trial for contempt but con-
victed and sentenced after. The district court summarily
convicted and sentenced Schiff at the time each of the fifteen
separate contumacious acts occurred. The record clearly
shows that Schiff was informed in advance of the progressive
punishment that would be imposed for each repeated act in
contempt of the district court’s mid-trial rulings committed in
the presence of the court and the jury. He was not entitled to
relitigate his misbehavior after the trial because each mid-trial
contempt conviction and sentence became final at the time the
                   UNITED STATES v. COHEN                16717
contemptuous conduct occurred, and he was summarily sanc-
tioned for it as the district judge tried as best he could to
maintain order and coerce Schiff into complying with his rul-
ings.

   Schiff relies primarily on Taylor v. Hayes, 418 U.S. at 488.
There, a state court judge “informed” an attorney nine times
during a trial that he was in contempt of court, but did not
sentence the attorney for those convictions until after the
trial’s conclusion, when he imposed a combined sentence of
four and a half years in prison, though that sentence was ulti-
mately reduced by about one year. Id. at 490-94. At the time
of sentencing, the judge did not permit the lawyer to speak in
his own defense. Id. at 490. On appeal, the lawyer contended
that the due process clause entitled him to notice and an
opportunity to be heard prior to final conviction and sentence.
Id. at 496. The Court agreed.

   The Court began its analysis by noting that the case before
it did not involve the trial judge’s exercise of his summary
contempt power. Id. at 497 (“We are not concerned here with
the trial judge’s power, for the purpose of maintaining order
in the courtroom, to punish summarily and without notice or
hearing contemptuous conduct committed in his presence and
observed by him.”) (citation omitted). The Court observed
that

    [N]o sentence was imposed during the trial, and it
    does not appear to us that any final adjudication of
    contempt was entered until after the verdict was
    returned. It was then that the [trial judge] proceeded
    to describe and characterize petitioner’s various acts
    during trial as contemptuous, to find him guilty of
    nine acts of contempt, and to sentence him immedi-
    ately for each of those acts.

Id. The Court devotes the remainder of its opinion to explain-
ing why, in the context of a non-summary contempt convic-
16718               UNITED STATES v. COHEN
tion, the contemnor is entitled to “reasonable notice of the
specific charges and opportunity to be heard in his own
behalf.” Id. at 499 (citing Groppi v. Leslie, 404 U.S. 496, 506
& n.11 (1948)).

  Unlike the trial court in Taylor, the district court convicted
and punished Schiff immediately as each act of contempt
occurred. During the first eight days of trial, the district court
warned Schiff innumerable times to obey court orders. On the
ninth day, after Schiff continued to disregard the court’s
admonishments, the court explicitly held Schiff in criminal
contempt and punished him immediately by imposing one day
of incarceration. We have no difficulty concluding that this
constituted a final adjudication and punishment for the first
contumacious act that occurred in the court’s presence.

   [4] The closer question is whether the district court’s sim-
ple utterance of the word “sanction” after each of the subse-
quent fourteen contumacious acts in an apparent attempt to
prevent Schiff’s contemptuous behavior from distracting the
jury, constitutes a final adjudication and sentencing. We hold
that it does. At the time of the first contempt conviction, the
district court expressly provided Schiff with a formula for
determining the punishment that would attach to further acts
of contempt. Under that formula, he was fairly warned that
the sentence imposed for each successive contumacious act
doubled. The district court also informed Schiff at the time of
the first contemptuous act that rather than bring the proceed-
ings to a halt each time Schiff engaged in contempt of the
court’s rulings, the district court would simply state “sanc-
tions.” That word thus had a two-fold meaning: first, it meant
that Schiff was being held in criminal contempt; second, it
provided, based on the punitive formula previously
announced, the specific punishment for each act of contempt.
We see nothing wrong with a district court employing such
progressive punishment and providing fair warning in
advance to the contemnor in order to curb persistent miscon-
duct and maintain order in the proceedings.
                    UNITED STATES v. COHEN                 16719
   When the district court stated “sanctions,” that word did not
denote simply a citation whose implications would be dis-
cussed after trial in conjunction with other contempt citations.
Rather, the district court treated each instance of contemptu-
ous conduct as a “discrete and separate matter,” Codispoti,
418 U.S. at 515, and punished each act at the time it occurred.
Each conviction and each punishment attempted to serve the
immediate and compelling need to preserve order and “pre-
vent ‘demoralization of the court’s authority.’ ” In re Oliver,
333 U.S. 257, 275 (1948) (quoting Cooke v. United States,
267 U.S. 517, 536 (1925)). That it did not have the desired
effect on Schiff is regrettable. But the manner in which the
contempt and related punishment were imposed do not pro-
vide grounds upon which to excuse what he did in the face of
fair warning.

   Our conclusion is not altered by the fact that after the trial,
the district court chose to reduce the respective punishments
for ten of the contempt convictions to one month each. The
function of that hearing was not to determine whether Schiff
should be held in criminal contempt, and if so, to impose a
sentence. Schiff had already been convicted and sentenced on
fifteen separate occasions. Rather, the function of that hearing
was to sentence Schiff for the guilty verdicts that the jury had
returned on the tax and conspiracy counts charged in the
indictment, to add up the fifteen contempt sentences Schiff
had already received, and to determine whether the sentences
should run concurrently or consecutively. The district court’s
discretionary decision to remit the punishments for some of
those later mid-trial contempt convictions does not, in our
view, bring this case into line with those such as Taylor and
Codispoti, where the contemnor was cited during the trial, and
the final decision of whether to hold him in criminal con-
tempt, and if so, the punishment to be imposed for that crime,
was deferred until the trial’s conclusion. The concerns
expressed in Taylor and its progeny about the “heightened
potential for abuse posed by contempt power,” Taylor, 418
16720              UNITED STATES v. COHEN
U.S. at 500, are not implicated when a court reduces a consti-
tutional, earlier-imposed sentence.

   [5] In sum, we conclude that Schiff was summarily cited
and contemporaneously sentenced fifteen separate times dur-
ing the trial for criminal contempt. As a result, he was not
entitled under the Fifth Amendment’s Due Process Clause to
additional notice or an opportunity to be heard with respect to
contesting those convictions or the summary punishments
imposed at the post-trial sentencing hearing. See Taylor, 418
U.S. at 498-99. Also, because none of the individual sen-
tences exceeded six months, he was not entitled under the
Sixth Amendment to have a jury determine his guilt before
punishment was imposed on those contumacious acts commit-
ted in direct defiance of the trial judge’s rulings. See
Codispoti, 418 U.S. at 514 (noting that the right to trial by
jury does not attach where a person is summarily convicted
and sentenced during the trial on multiple occasions, as long
as each sentence does not exceed six months).

                              II

                              A

   The more troublesome issue we address concerns the dis-
trict court’s handling of proffered expert psychiatric evidence
on behalf of appellant Cohen in the face of our precedent. On
June 14, 2005, Cohen’s lawyer filed a notice, pursuant to Fed-
eral Rule of Criminal Procedure 12.2, that he intended to offer
expert testimony by psychiatrist Dr. Norton A. Roitman relat-
ing to Cohen’s “mental disease . . . bearing on . . . the issue
of guilt.” Attached to that notice was a report prepared by Dr.
Roitman, who had met with Cohen on two occasions at the
request of Cohen’s attorney.

   In the report, Dr. Roitman diagnoses Cohen as suffering
from a narcissistic personality disorder, and concludes that
Cohen “did not intend to violate the law, as would be the case
                    UNITED STATES v. COHEN                 16721
with a criminal who acted out of a desire for personal gain”
but rather “[h]is behavior is driven by a mental disorder as
opposed to criminal motivation . . . Although it is true Mr.
Cohen was not delusional or psychotic and was in possession
of basic mental faculties, his will was in the service of irratio-
nal beliefs as a result of narcissistic personality disorder.” The
report also notes that

    Because [Cohen’s] beliefs are fixed and have led
    him to significant adverse consequences, he is irra-
    tional to the point of dysfunction, demonstrated by
    his stubborn adherence in the face of overwhelming
    contradictions and knowledge of substantial penalty.
    . . . Despite evidence to the contrary, his psychologi-
    cal needs dominated his mentation. . . . This is the
    nature of the narcissistic personality in which the
    sufferer could essentially pass a lie detector test
    when asked commonsensical questions while giving
    improbable answers.

   The government moved to bar Dr. Roitman from testifying
and the district court agreed, reasoning that Dr. Roitman
failed to explain “how the alleged mental disorders negate
mens rea. Rather, [his] opinion[ ] merely explain[s] or justif-
[ies] [Cohen’s] conduct.”

                                B

   “We review for abuse of discretion a district court’s deci-
sion to admit or exclude scientific evidence.” United States v.
Finley, 301 F.3d 1000, 1007 (9th Cir. 2002) (citation omit-
ted). “A district court abuses its discretion when it bases its
decision on an erroneous view of the law or a clearly errone-
ous assessment of the facts.” United States v. Campos, 217
F.3d 707, 710 (9th Cir. 2000) (citation omitted).
16722                   UNITED STATES v. COHEN
                                      C

   [6] Federal Rules of Evidence 702 and 704(b) govern the
admissibility of Dr. Roitman’s testimony, and we examine the
exclusion of his testimony under both of these rules.5 See,
e.g., Finley, 301 F.3d at 1012-16 (examining the district
court’s decision to exclude expert testimony from the defen-
dant’s psychologist under Rules 702 and 704(b)); United
States v. Morales, 108 F.3d 1031, 1035 (9th Cir. 1997) (en
banc). “If the evidence could have been excluded under either
rule, the district court did not abuse its discretion.” Morales,
108 F.3d at 1035.

                                      1

   [7] The threshold issue is whether Dr. Roitman’s testimony
would have assisted the trier of fact within the meaning of
Rule 702. According to Cohen, Dr. Roitman’s testimony
would have bolstered the contention that Cohen had a good
faith belief that he was acting in accordance with the law,
thereby negating the mens rea element of 26 U.S.C.
§ 7206(2), which requires that a defendant “[w]illfully”6 assist
in the filing of a false return. See Cheek v. United States, 498
U.S. 192, 201 (1991) (holding that a defendant cannot be con-
victed of violating a federal tax law if he harbors a good faith
belief that he was not violating any of the provisions of the
  5
     Rule 702 provides, “If scientific . . . knowledge will assist the trier of
fact to understand the evidence or to determine a fact in issue, a witness
qualified as an expert . . . may testify thereto in the form of an opinion or
otherwise.” Rule 704(b) prohibits the expert from offering “an opinion or
inference as to whether the defendant did or did not have the mental state
or condition constituting an element of the crime charged or of a defense
thereto.”
   6
     “Willfulness requires that an act be done knowingly and intentionally,
not through ignorance, mistake or accident.” Morales, 108 F.3d at 1037
(citing Ninth Circuit Manual of Model Jury Instructions - Criminal, 5.05
(West 1995)). That is, Cohen had to know that the tax returns he assisted
in filing were false. Id.
                    UNITED STATES v. COHEN                 16723
tax laws). The government counters that Dr. Roitman’s report
was irrelevant because nothing in it suggested

    that defendant was not capable of forming the requi-
    site mens rea for the charged offenses. On the con-
    trary, as the District Court found, Dr. Roitman’s
    report did no more than explain why defendant
    intentionally violated his known legal duties. The
    report does not remotely suggest that defendant
    lacked the mental aptitude to understand his legal
    duties or the ability to act volitionally.

   Cohen argues that United States v. Finley, 301 F.3d at
1000, controls and we agree. There, Finley was seeking fund-
ing to open a chain of bookstores when he met Leroy
Schweitzer, a supposed investment guru who claimed to have
recorded liens against various banks which could be drawn
upon by the issuance of certain negotiable instruments. Id. at
1002-03. Schweitzer gave Finley several of these bogus
instruments, claiming that they were worth nearly seven mil-
lion dollars. Id. at 1003. Every institution presented with one
of these instruments refused to honor it, including the IRS. Id.
at 1003-04. Finley persisted in attempting to pay off his tax
debt with these instruments, and he was eventually prosecuted
for, inter alia, making a false claim against the United States
in violation of 18 U.S.C. § 287. Id. at 1002, 1004. At trial, the
district court excluded under Rule 702 testimony from Fin-
ley’s psychologist that Finley lacked the intent to defraud due
to his delusional disorder “in which . . . information from the
real world . . . is so grossly distorted that the person ends up
with” bizarre, irrational and fixed beliefs. Id. at 1006 (internal
quotation marks omitted).

  We reversed, reasoning that the excluded testimony

    would have offered an explanation as to how an oth-
    erwise normal man could believe that these financial
    instruments were valid and reject all evidence to the
16724               UNITED STATES v. COHEN
    contrary. While Finley could and did testify about
    how and why he believed the instruments were valid,
    only a trained mental health expert could provide a
    counterweight to the government’s allegations
    against Finley.

Id. at 1013.

   [8] The facts in Finley are strikingly similar to those in the
present case. Schweitzer convinced Finley that certain finan-
cial instruments were genuine; Schiff convinced Cohen that
one could legally submit a zero return. Expert testimony prof-
fered by Finley and Cohen suggested they had a tendency to
cling doggedly to their beliefs even in the face of overwhelm-
ing contradictions. The Finley court determined that the
expert testimony could have helped the defendant counter the
government’s argument that he knew the financial instru-
ments were false; similarly, Dr. Roitman’s testimony would
have helped Cohen counter the government’s suggestion that
Cohen knew the zero returns were false.

   [9] We disagree with the government that Dr. Roitman’s
report can only be read to mean that Cohen knew what he was
doing was wrong but did it anyway. In fact, the opposite is
true: a fair reading of Dr. Roitman’s report suggests that once
Cohen adopted Schiff’s views, Cohen would not change his
mind. The report specifically states that Cohen “did not intend
to violate the law.” If Dr. Roitman had been allowed to testify
to that effect, his testimony would have assisted the trier of
fact within the meaning of Rule 702.

   The government’s reliance on United States v. Scholl, 166
F.3d 964, 970 (9th Cir. 1999), is misplaced. There, a defen-
dant charged with filing false tax returns argued that the dis-
trict court had erred in excluding under Rule 702 the
testimony of an expert on compulsive gambling who would
have testified that pathological gamblers, like the defendant,
“have distortions in thinking and ‘denial,’ which impact their
                    UNITED STATES v. COHEN                 16725
ability and emotional wherewithal to keep records.” Id. We
affirmed, noting that there was no evidence presented at the
Daubert hearing that addicted gamblers were incapable of
truthfully reporting their gambling income. Id. “[E]vidence
that compulsive gamblers are in denial . . . would not tend to
show that Scholl did not believe his tax return to be correct
. . . .” Id. at 971.

   Scholl is easily distinguishable from the present case.
According to his expert’s report, a narcissistic personality dis-
order like Cohen’s can cause a person to continue to believe
something to be true despite overwhelming evidence of its
patent absurdity. By contrast, there was no evidence in Scholl
that an addiction to gambling could cause a person to believe
that a false tax return omitting winnings was true.

   Neither United States v. Byers, 730 F.2d 568 (9th Cir.
1984), nor United States v. Demma, 523 F.2d 981 (9th Cir.
1975) (en banc), require a different conclusion. In both cases,
we upheld the exclusion of psychiatric testimony offered to
negate the defendant’s mens rea due to the “ ‘wide latitude
[afforded to the district court] in admitting or excluding psy-
chiatric evidence directed to the capacity of a defendant to
entertain a specific intent.’ ” Byers, 730 F.2d at 571 (quoting
Demma, 523 F.2d at 986). In Byers, the psychiatric testimony
was “ambiguous” and would not “have materially assisted a
jury in determining whether Byers committed a voluntary,
intentional violation of known legal duty.” Id. (citations omit-
ted). By contrast, there is no such ambiguity in Dr. Roitman’s
report. The only question, which we discuss below, is how far
Dr. Roitman should have been permitted to go in explaining
his expert conclusions as they related to Cohen’s ability to
form the intent to evade the tax laws.

                               2

   [10] Rule 704(b) is a limitation on Rule 702. Even if expert
testimony would “assist the trier of fact” within the meaning
16726               UNITED STATES v. COHEN
of Rule 702, such testimony may be excluded under Rule
704(b) if the testimony “state[s] an opinion or inference as to
whether the defendant did or did not have the mental state or
condition constituting an element of the crime charged . . . .”
Fed. R. Evid. 704(b). With respect to the type of inference
precluded under Rule 704(b), the court has stated that the
expert may not “draw[ ] an inference which would necessarily
compel the conclusion” that the defendant lacked the requisite
mens rea. Morales, 108 F.3d at 1037.

   United States v. Morales, 108 F.3d at 1033, and United
States v. Finley, 301 F.3d at 1016, serve as persuasive author-
ity. In Morales, the defendant was charged with willfully
making false entries in a union ledger in violation of 29
U.S.C. § 439(c). 108 F.3d at 1033. At trial, a key issue was
“whether her admitted bookkeeping inaccuracies were inten-
tional or were the result of her ignorance of proper bookkeep-
ing procedures.” Id. at 1034. In support of her argument that
the errors were not willful, Morales proffered expert testi-
mony from a certified public accountant who would have tes-
tified regarding Morales’s poor level of knowledge and
understanding of bookkeeping principles. Id. The district
court excluded the evidence under Rule 704(b) but we
reversed, reasoning that the expert “was not going to state an
opinion or draw an inference that Morales did not intend to
make false entries. Rather, she was going to state her opinion
as to a predicate matter — that Morales had a weak grasp of
bookkeeping principles. . . . Even if the jury believed . . . [the
expert], the jury would still have had to draw its own infer-
ence from that predicate testimony to answer the ultimate fac-
tual question.” Id. at 1037.

  In Finley, we concluded that the psychologist’s testimony
did not violate Rule 704(b) because

    The jury could have accepted the atypical belief
    diagnosis and still concluded that Finley knowingly
    defrauded the banks. If credited, [the expert’s] testi-
                    UNITED STATES v. COHEN                16727
    mony established only that Finley’s beliefs were
    rigid and he would distort or disregard information
    that ran counter to those beliefs. [The expert] did
    not, and would not be allowed to, testify about Fin-
    ley’s specific beliefs with regard to the [bogus]
    financial instruments. The jury was free to conclude
    that Finley knew the notes were fraudulent, despite
    the rigidity of his belief system.

301 F.3d at 1015-16.

   [11] We have little doubt that if Dr. Roitman had been per-
mitted to testify as to all of the conclusions contained in his
report, some of that proffered testimony as contained in his
report would have invaded the province of the jury and vio-
lated Rule 704(b). However, the best way for the district court
to have insured the exclusion of the potentially inadmissible
aspects of Dr. Roitman’s testimony was not to bar him from
testifying altogether, but to sustain the government’s objec-
tions to particular questions likely to elicit inadmissible evi-
dence under the rule. The district court also could have
discussed with the parties before he testified the limits that
would be imposed on the scope of Dr. Roitman’s testimony.
See Finley, 301 F.3d at 1005.

  If the district court had followed that course of action, then
Dr. Roitman’s testimony, like the expert testimony at issue in
Morales and Finley, would have gone to a predicate matter —
whether Cohen suffered from a Narcissistic Personality Disor-
der. Even if the jury had accepted this diagnosis, the jury
would still have been required to determine what impact, if
any, that condition might have on Cohen’s ability to form the
requisite mens rea — the intent to evade the tax laws. As in
Finley, the jury could have accepted the Roitman diagnosis
but determined nonetheless that Cohen knew the zero returns
were false.

  The government relies on United States v. Campos, 217
F.3d at 710-12, in which we affirmed a decision to exclude
16728                   UNITED STATES v. COHEN
testimony by the defendant’s expert polygraph examiner that
the defendant did not know that she was transporting mari-
juana into the United States. Such testimony, according to the
Campos court, “falls squarely within the scope of Rule
704(b)” because, if the testimony was credited, it “necessarily
follows” that the defendant lacked the requisite mens rea. Id.
at 711.

   Campos is easily distinguishable. If Dr. Roitman’s testi-
mony was limited in the manner described above, the jury
could still have concluded that Cohen knew the zero returns
were false but chose nevertheless to assist others in filing
them. But in Campos, if the jury believed the polygraph
expert, the conclusion that the defendant lacked the requisite
mens rea was inescapable.

                                     3

   [12] The government argues that even if Dr. Roitman’s tes-
timony was admissible under Rules 702 and 704(b), it should
have been excluded under Rule 403.7 We disagree. Dr. Roit-
man’s testimony would have been highly probative on the
issue of whether Cohen could have formed the requisite mens
rea, and was unlikely to cause significant confusion with the
jury if properly constrained by compliance with the rules of
evidence.

                                     4

   “Under our test for nonconstitutional error, which we apply
to errors as to the admissibility of expert testimony, we must
reverse unless it is more probable than not that the error did
not materially affect the verdict.” United States v. Rahm, 993
F.2d 1405, 1415 (9th Cir. 1993) (citation omitted).
  7
   Federal Rule of Evidence 403 provides that relevant evidence may be
excluded “if its probative value is substantially outweighed by the danger
of unfair prejudice, confusion of the issues, or misleading the jury . . . .”
                    UNITED STATES v. COHEN                    16729
   [13] The court in Finley concluded that the exclusion of the
expert’s testimony was not harmless because that testimony
was “essential to the defense.” 301 F.3d at 1018. “Finley’s
counsel did not have any other way of explaining the possibil-
ity that Finley suffered from a mental disorder.” Id.; see also
Morales, 108 F.3d at 1040 (holding that the wrongful exclu-
sion of the defendant’s expert witness who would have
offered evidence that the defendant lacked the requisite mens
rea was not harmless error); Rahm, 993 F.2d at 1415 (con-
cluding that the wrongful exclusion of the defendant’s expert
witness, a psychologist who would have testified that the
defendant suffered from “perceptual difficulties” and was
therefore less likely to know that the currency in question was
counterfeit, was not harmless error). Likewise, the exclusion
of Dr. Roitman’s testimony left Cohen without any way to
explain the effect that his mental disorder may have had on
his ability to form the requisite mens rea. We therefore
reverse Cohen’s conviction, vacate his sentence, and remand
for a new trial.

                                III

   Schiff’s criminal contempt convictions are vacated, and the
case is remanded to allow the district court to file the requisite
contempt orders pursuant to Federal Rule of Criminal Proce-
dure 42(b). Any sentence reimposed must not exceed eleven
months. The district court retains the discretion to impose the
contempt punishment to run consecutively to the sentence for
the tax convictions. Cohen’s conviction is reversed, his sen-
tence vacated, and the case is remanded for a new trial. The
remaining issues are addressed in the accompanying memo-
randum disposition.

  AFFIRMED         in   part,   REVERSED         in   part,    and
REMANDED.
