                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  No. 04-50618
                Plaintiff-Appellee,
               v.                            D.C. No.
                                          CR-04-01463-JAH
LOUIS JOSEPH BAHAMONDE,
                                             OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
          for the Southern District of California
        John A. Houston, District Judge, Presiding

                  Argued and Submitted
           August 2, 2005—Pasadena, California

                   Filed April 25, 2006

     Before: William C. Canby, Jr., Alex Kozinski, and
           Johnnie B. Rawlinson, Circuit Judges.

                 Opinion by Judge Canby;
                Dissent by Judge Rawlinson




                           4595
4598           UNITED STATES v. BAHAMONDE


                      COUNSEL

Kurt D. Hermansen, Federal Defenders of San Diego, Inc.,
San Diego, California, for the appellant.
                    UNITED STATES v. BAHAMONDE                     4599
Stephen R. Cook, Assistant United States Attorney, San
Diego, California, for the appellee.


                              OPINION

CANBY, Circuit Judge:

   Louis Bahamonde appeals his jury convictions for know-
ingly importing marijuana and possession of marijuana with
intent to distribute. 21 U.S.C. §§ 841(a)(1), 952, 960. Baha-
monde contends that the district court erred by excluding the
testimony of the government’s case agent, called by the
defense, on the sole ground that Bahamonde failed to comply
with the Department of Homeland Security’s regulations gov-
erning testimony by its employees. We reverse for two rea-
sons: (1) the regulation, which required disclosure by
Bahamonde without reciprocal disclosure by the government,
violated Bahamonde’s due process rights, and (2) the district
court abridged Bahamonde’s Sixth Amendment rights by
imposing the severe sanction of exclusion of the agent’s entire
testimony without weighing the countervailing interests, such
as Bahamonde’s constitutional rights, prejudice to his
defense, or the availability of alternative sanctions.1

                          BACKGROUND

   In the Southern District of California, a grand jury indicted
Bahamonde for knowingly importing marijuana and posses-
sion of marijuana with intent to distribute. 21 U.S.C.
§§ 841(a)(1), 952, 960. A jury convicted him of both counts.
   1
     Bahamonde also contends that the indictment must be dismissed
because of improper instructions to the grand jury, but this challenge is
foreclosed by our recent decision in United States v. Navarro-Vargas, 408
F.3d 1184 (9th Cir.) (en banc), cert. denied, 126 S. Ct. 736 (2005). Our
disposition of this appeal makes it unnecessary for us to address Baha-
monde’s other contentions.
4600             UNITED STATES v. BAHAMONDE
The district court sentenced him to twenty-seven months in
prison on each count, to run concurrently, followed by three
years of supervised release.

   Bahamonde was convicted because, four hours after driving
from California into Tijuana, Mexico, he attempted to drive
back into the United States carrying twenty-seven kilograms
of marijuana hidden in his car. Customs and Border Protec-
tion Officers stopped Bahamonde’s car and searched it
because Bahamonde appeared nervous at the port of entry.
The case agent, Don Rodmel, interviewed Bahamonde,
arrested him, and conducted the investigation leading to
Bahamonde’s prosecution.

   During questioning and at trial, Bahamonde maintained
that, although there was a large quantity of marijuana hidden
in the car, he did not know it was there. He contended that the
acquaintance from whom he had bought the car, Raul Fuen-
tes, must have hidden the marijuana in the car without telling
Bahamonde. He further contended that, at the time of its
investigation of Bahamonde’s case, the government possessed
substantial information about Fuentes, including his involve-
ment in transporting controlled substances across the border.
Bahamonde sought to show that the government failed to
investigate the possibility that Fuentes, and not Bahamonde,
was the guilty party and that this failure resulted in the wrong
man being prosecuted.

   Agent Rodmel attended the entire trial, sat next to the pros-
ecutor at the prosecutor’s table, assisted him throughout, and
was listed on the government’s witness list. When Baha-
monde attempted to call Agent Rodmel as a witness, however,
the government objected on the sole ground that Bahamonde
had failed to comply with 6 C.F.R. § 5.45(a) (requiring a liti-
gant to “set forth in writing, and with as much specificity as
possible, the nature and relevance of the official information
sought” from Department of Homeland Security witnesses).
                    UNITED STATES v. BAHAMONDE                        4601
   When the district judge asked Bahamonde’s counsel why
he had failed to comply, Bahamonde’s counsel stated that he
believed that the regulation was not a requirement; he merely
followed it sometimes as a courtesy to the government. Baha-
monde’s counsel stated, however, that he would “be happy to
give [Agent Rodmel] a C.F.R. letter right now.” The district
court ruled that this offer to comply was untimely, and
excluded the agent’s testimony. In later denying Bahamonde’s
motion for a mistrial, the district judge specified that he
excluded the witness because Bahamonde’s counsel knew of
the regulation and of the fact that he would need Agent Rod-
mel’s testimony, but failed to comply with the regulation.

                              ANALYSIS

  We conclude that the district court erred in excluding the
agent’s testimony for two reasons.2

  A.    The Regulation Violates Wardius’s Reciprocal
        Discovery Requirement

  [1] The regulation of the Department of Homeland Security
provides, in part:

      If official information is sought, through testimony
      or otherwise, by a request or demand, the party seek-
      ing such . . . testimony must . . . set forth in writing,
      and with as much specificity as possible, the nature
      and relevance of the official information sought. . . .
      Department employees may only . . . testify concern-
  2
   We review de novo whether the district court violated Bahamonde’s
due process or compulsory process rights. See Guam v. Palomo, 35 F.3d
368, 374 (9th Cir. 1994), overruled on other grounds by United States v.
Galindo-Gallegos, 255 F.3d 1154 (9th Cir. 2001); United States v. Lewis,
979 F.2d 1372, 1374 (9th Cir. 1992). In other respects, we review for an
abuse of discretion whether the district court erred by admitting or exclud-
ing evidence. United States v. Hernandez, 109 F.3d 1450, 1452 (9th Cir.
1997) (per curiam).
4602                 UNITED STATES v. BAHAMONDE
      ing those matters which were specified in writing
      and properly approved by the appropriate Depart-
      ment official designated in § 5.44.

6 C.F.R. § 5.45(a).3 4 The regulation contains no requirement
that the government specify the nature of testimony or other
evidence that it intends to use to rebut the demanded testi-
mony.

  [2] The regulation, as applied in this criminal prosecution,
violates due process by failing to provide reciprocal discov-
ery. The governing principle is established by Wardius v.
Oregon, 412 U.S. 470 (1973). In Wardius, the Supreme Court
addressed Oregon’s requirement that a criminal defendant
seeking to offer alibi evidence give notice in advance, “which
  3
   The subsection provides in full:
     (a) If official information is sought, through testimony or other-
     wise, by a request or demand, the party seeking such release or
     testimony must (except as otherwise required by federal law or
     authorized by the Office of the General Counsel) set forth in writ-
     ing, and with as much specificity as possible, the nature and rele-
     vance of the official information sought. Where documents or
     other materials are sought, the party should provide a description
     using the types of information suggested in § 5.3(b). Subject to
     § 5.47, Department employees may only produce, disclose,
     release, comment upon, or testify concerning those matters which
     were specified in writing and properly approved by the appropri-
     ate Department official designated in § 5.44. See United States ex
     rel. Touhy v. Ragen, 340 U.S. 462 (1951). The Office of General
     Counsel may waive the requirement of this subsection in appro-
     priate circumstances.
  4
    Section 5.45(a) does not create a privilege against divulging evidence
because its enabling statute, 5 U.S.C. § 301, states that “[t]his section does
not authorize withholding information from the public or limiting the
availability of records to the public.” See Exxon Shipping Co. v. United
States Dep’t of Interior, 34 F.3d 774, 778 (9th Cir. 1994). The Supreme
Court in a civil case has held, however, that a government agency can
require employees to secure approval of the agency head before respond-
ing to a subpoena. See United States ex rel. Touhy v. Ragen, 340 U.S. 462,
467-68 (1951).
                     UNITED STATES v. BAHAMONDE                        4603
notice shall state specifically the place or places where the
defendant claims to have been at the time or times of the
alleged offense together with the name and residence or busi-
ness address of each witness upon whom the defendant
intends to rely for alibi evidence.” Or. Rev. Stat. § 135.875
(since renumbered as § 135.455). The statute imposed no
reciprocal requirement on the State to provide names and
addresses of witnesses the State intended to call to rebut the
alibi. The Supreme Court held that this imbalance of discov-
ery requirements violated due process when the statute was
invoked to exclude the testimony of the defendant’s alibi wit-
ness. Wardius, 412 U.S. at 472. The Court stated:

      It is fundamentally unfair to require a defendant to
      divulge the details of his own case while at the same
      time subjecting him to the hazard of surprise con-
      cerning refutation of the very pieces of evidence
      which he disclosed to the State.

Id. at 476. This same unfairness inheres in the present crimi-
nal case. Bahamonde was required to state with specificity the
testimony he expected from Agent Rodmel but the govern-
ment was not required at any time to state what evidence it
expected to offer in rebuttal, either from Rodmel or anyone else.5
Nor was there any other requirement in force to compel the
government to reveal that information. See FED. R. CRIM. P.
16 (requiring statements of expected testimony only with
regard to expert witnesses).
  5
    The dissenting opinion here contends that Wardius is inapplicable
because the Department of Homeland Security regulation “was promul-
gated, not as a discovery device, but as a means to control the flow of
information from the agency and insure that no information was disclosed
that should have remained secreted.” Infra, p. 4609. But the regulation
sought not only to control the release of information; it required disclosure
of information from Bahamonde without offering corresponding informa-
tion. That kind of imbalance is what Wardius viewed as fundamentally
unfair.
4604                 UNITED STATES v. BAHAMONDE
   [3] The government points to two differences between
Wardius and this case. First, Washington “grant[ed] no dis-
covery rights to criminal defendants, and indeed, [did] not
even provide defendants with bills of particulars.” Wardius,
412 U.S. at 475. Federal criminal prosecutions, on the other
hand, allow for liberal discovery. Second, whereas alibi
defenses frequently involve people and places unrelated to the
charged offenses, and thus potentially not covered by tradi-
tional discovery rules, the information Bahamonde sought
from Agent Rodmel was available to both parties through the
regular discovery process. According to the government, forc-
ing the defendant to disclose what he planned to ask Agent
Rodmel didn’t give the government any practical advantage.
Wardius held, though, “that in the absence of a strong show-
ing of state interests to the contrary, discovery must be a two-
way street,” and “if there is to be any imbalance in discovery
rights, it should work in the defendant’s favor.” Id. at 475 &
n.9. Nothing in Wardius limits its reasoning to alibi defenses
or trial processes entirely lacking in discovery.

   [4] The regulation, as applied in this case, accordingly falls
squarely within the rule of Wardius.6 We cannot say, on this
record, that this constitutional error was harmless beyond a
  6
    Our decision does not address the validity of the regulation in other cir-
cumstances or contexts. See, e.g., Ragen, 340 U.S. at 467-68 (upholding,
in a civil case, order of Department of Justice prohibiting employees from
responding to subpoenas without permission of the Attorney General or
his Assistants). Nor does our decision conflict with United States v. Hen-
son, 123 F.3d 1226 (9th Cir. 1997), overruling on other grounds recog-
nized by United States v. Foster, 165 F.3d 689, 692 n.5 (9th Cir. 1999) (en
banc). In Henson, the district court quashed the defendant’s subpoena of
a Bureau of Alcohol, Tobacco, and Firearms (ATF) policy manual “be-
cause the evidence could be obtained by questioning the witnesses direct-
ly” and “because Henson did not follow the procedures for obtaining ATF
records outlined” in the regulation. Id. at 1237. The panel affirmed
because “[t]here was nothing to prevent Henson from immediately serving
another subpoena on the ATF that followed the ATF guidelines.” Id. And
Henson was allowed to cross-examine witnesses on the contents of the
manual. Henson did not address a situation where the defendant was
required to state precisely how he planned to use the evidence at trial, and
thus, quashing the subpoena did not implicate Wardius. Here we deal only
with the application of the regulation requiring a criminal defendant to
state how he plans to use material evidence when the government is under
no reciprocal discovery obligation.
                 UNITED STATES v. BAHAMONDE                 4605
reasonable doubt. See Chapman v. California, 386 U.S. 18, 24
(1967) (stating standard for harmlessness of constitutional
error). The marijuana was hidden behind the rear seat (the
inspector felt a hard spot in the seat and used a screwdriver
to pry the backrest aside to reveal the marijuana), in the spare
tire, in the rear bumper, and in the rear door panels. We can-
not say beyond a reasonable doubt that a jury would reject a
defense based on testimony that the government failed to
investigate the possibility that the former owner, a drug traf-
ficker, had left the marijuana in the car without the knowledge
of Bahamonde. We accordingly reverse Bahamonde’s convic-
tion. See Wardius, 412 U.S. at 479.

  B.   Bahamonde Can Challenge the Regulation Without
       Having Attempted to Comply With It

   The government defends the district court’s ruling by rely-
ing primarily on three cases from other circuits, each of which
precluded a defendant from challenging a very similar regula-
tion because he had made no attempt to comply with its
requirements and secure a determination whether the govern-
ment agency would make the information available. See
United States v. Allen, 554 F.2d 398, 406-407 (10th Cir.
1977); United States v. Marino, 658 F.2d 1120, 1125-26 (6th
Cir. 1981) (following Allen but also noting that excluded evi-
dence was not “material”); United States v. Wallace, 32 F.3d
921, 928-29 (5th Cir. 1994) (following Allen and Marino but
also noting that excluded evidence was “cumulative and mar-
ginally relevant”). None of these cases, however, addresses
the problem of imbalance of discovery obligations that were
found to cause a constitutional violation in Wardius, and it is
not clear that this issue was directly raised in the three cases.

   [5] The issue is squarely raised here, however, and Wardius
itself provides the answer. In Wardius, the government argued
that, because the defendant did not comply with the discovery
rule, he should not be allowed to challenge it as violating due
process, particularly because the state courts might have read
4606             UNITED STATES v. BAHAMONDE
a reciprocal discovery right into the statute and avoided the
constitutional issue. Wardius, 412 U.S. at 477. The Court
rejected this argument because it was speculative, and permit-
ted the defendant to challenge the statute without complying
with its disclosure requirements. Id. At 477-78. The Court
stated:

    To be sure, the state court might have construed the
    Oregon statutes so as to save the constitutionality of
    the notice requirement and granted reciprocal dis-
    covery rights. But the state court would also have
    had the option of reading state law as precluding
    reciprocal discovery. If the court adopted this latter
    alternative, it would have had to strike down the
    notice-of-alibi requirement. But petitioner would
    have had only a Pyrrhic victory, since once having
    given the State his alibi information, he could not
    have retracted it. Thus, under this scenario, even
    though the notice-of-alibi rule would have been
    invalidated, the State would still have had the benefit
    of nonreciprocal discovery rights in petitioner’s case
    — the very result which petitioner wishes to avoid
    by challenging the rule.

    . . . [P]etitioner cannot be faulted for taking the legis-
    lature at its word.

Id. Here, too, Bahamonde cannot be faulted for taking the reg-
ulation as written, with its absence of any requirement of
reciprocal discovery. He need not reveal the nature of his
anticipated defense testimony in order to challenge the regula-
tion that improperly requires him to reveal such testimony. If
such a challenge succeeded, he still would have revealed his
defense. We accordingly permit him to challenge the regula-
tion without first complying with its threshold disclosure
requirement.
                  UNITED STATES v. BAHAMONDE                 4607
  C.   The District Court Abused Its Discretion By Failing
       To Weigh Countervailing Interests Before
       Excluding Testimony

   [6] We require a district court, before excluding a defense
witness’s testimony, to balance the countervailing interests in
order to ensure that the exclusion complies with a criminal
defendant’s Sixth Amendment rights. See Eckert v. Tansy,
936 F.2d 444, 446 (9th Cir. 1991) (balancing interests);
Fendler v. Goldsmith, 728 F.2d 1181, 1187-90 (9th Cir.
1983); see also Taylor v. Illinois, 484 U.S. 400, 414-15
(1988). The factors to be weighed include “ ‘[t]he integrity of
the adversary process, which depends both on the presentation
of reliable evidence and the rejection of unreliable evidence;
the interests in the fair and efficient administration of justice;
. . . the potential prejudice to the truth determining function
of the trial process’ . . . the ease with which one can comply
with the statute[;] and whether failure to comply was willful
and motivated by a desire to gain a tactical advantage at trial.”
Eckert, 936 F.2d at 446 (alteration in original) (quoting Tay-
lor, 484 U.S. at 414-15). Additional (or, at least, differently
worded) considerations include “the effectiveness of less
severe sanctions, the impact of preclusion on the evidence at
trial and the outcome of the case, the extent of prosecutorial
surprise or prejudice, and whether the violation was willful.”
Taylor, 484 U.S. at 415 n.19 (citing Fendler, 728 F.2d at
1188-90). The “most significant” consideration is “how
important was the witness?” Fendler, 728 F.2d at 1188.

   [7] Agent Rodmel—the case agent—was very important.
He interviewed Bahamonde, arrested him and conducted the
investigation leading to criminal proceedings against Baha-
monde. With the exception of Raul Fuentes, Agent Rodmel
was the key player in the defense asserted by Bahamonde—
failure of the government to investigate possible third-party
culpability. See United States v. Sager, 227 F.3d 1138, 1145
(9th Cir. 2000) (noting the legitimacy and importance of a
defense of failure to investigate properly); United States v.
4608                UNITED STATES v. BAHAMONDE
Crosby, 75 F.3d 1343, 1349 (9th Cir. 1996) (noting the same
with respect to third-party culpability defense). The impor-
tance of Agent Rodmel to Bahamonde’s defense accordingly
weighs heavily in Bahamonde’s favor.

   [8] The remaining factors mostly weigh in Bahamonde’s
favor, but we do not belabor them because we are reversing
in any event for violation of Wardius’s rule. Having not
weighed any factors militating against exclusion of the wit-
ness, the district court abused its discretion. Moreover, the
government does not suggest that it was prejudiced by the
defendant’s failure to follow the regulation.7 Because the
exclusion of Rodmel’s testimony without weighing the coun-
tervailing interests impinged on his Sixth Amendment rights,
the error is constitutional. See Fendler, 728 F.2d at 1190. We
conclude that, like the constitutional error of applying the
Department’s regulation and for the same reasons, it is not
harmless beyond a reasonable doubt. See Chapman, 386 U.S.
at 24. This error, too, requires that we reverse Bahamonde’s
conviction and remand for a new trial.

                           CONCLUSION

  For the reasons stated, Bahamonde’s convictions are
reversed and the matter is remanded to the district court for
a new trial.

  REVERSED and REMANDED.



RAWLINSON, Circuit Judge, dissenting:

  I respectfully dissent. My primary disagreement with my
  7
   At oral argument, we learned that the prosecutor had complied with the
regulation and received permission from the Department of Homeland
Security to have Agent Rodmel testify (at least on certain topics).
                 UNITED STATES v. BAHAMONDE                4609
colleagues’ resolution of this case is their characterization of
the pivotal issue as one of reciprocal discovery, because I see
this case as involving the agency’s right to control the disclo-
sure of information within its custody.

   As the majority opinion relates, the Department of Home-
land Security (DHS) has promulgated a regulation that
requires one seeking official information from the agency to
describe, in writing, “the nature and relevance of the informa-
tion sought.” 6 C.F.R. § 5.45(a). The regulation was promul-
gated, not as a discovery device, but as a means to control the
flow of information from the agency and ensure that no infor-
mation was disclosed that should have remained secreted. The
regulation cites United States ex rel. Touhy v. Ragen, 340
U.S. 462 (1951), as supporting authority. The majority opin-
ion acknowledges, as it must, that Ragen upheld a Department
of Justice regulation prohibiting its employees from respond-
ing to a subpoena absent permission. See Majority Opinion,
p. 4604, n.6. The majority opinion then converts the issue into
one involving a discovery request, although neither the parties
nor the district court viewed it as such.

  Discovery in criminal cases is governed by a detailed, well-
defined, specific set of rules. See Fed. R. Cr. P. 16. The
evolvement of discovery in criminal cases is reflected in the
Advisory Committee Notes explaining the various amend-
ments to Rule 16. See id., Advisory Committee Notes. I
would not blithely transpose a regulation governing release of
documents into a non-sanctioned amendment of Rule 16. See
United States v. Alvarez, 358 F.3d 1194, 1207 n.8 (9th Cir.
2004) (confirming that Rule 16 governs discovery in criminal
cases and expressly excludes discovery of “statements made
by prospective government witnesses”) (citation omitted).

  This is not a case where Bahamonde made a discovery
request to the government which was improperly refused. Had
such been the case, the federal rules provide the district court
with an array of options to compel compliance. See, e.g. Fed.
4610             UNITED STATES v. BAHAMONDE
R. Cr. P. 16(d). Rather, in this case, counsel for Bahamonde
disregarded a regulation, of which he was well aware, to call
a witness, not to conduct pre-trial discovery.

   In my view, because this is not a discovery case, Wardius
v. Oregon, 412 U.S. 470 (1973), does not control the out-
come. Rather, this case is more akin to United States v. Allen,
554 F.2d 398 (10th Cir. 1977). In Allen, as in this case, the
defendant made no effort to comply with the regulation
requiring similar advance notice and summary of the desired
testimony. In upholding the trial court’s decision declining to
compel the testimony, the Tenth Circuit held:

       Our record shows no effort by defendant to submit
    the affidavit or statement summarizing the testimony
    desired so that the Department could consider the
    request and determine whether to grant permission
    for the testimony. In view of this, we feel that defen-
    dant is in no position to claim error in the court’s
    refusal to require testimony by the prosecutor. We
    feel that the regulation controlling such disclosures
    by Department of Justice employees is valid.

Id. at 407 (citations omitted) (emphasis added).

  A similar result is warranted in this case. Bahamonde was
not requesting pretrial discovery. He was seeking to call a
witness without meeting the requirements of a regulation of
which he was indisputably aware. I would follow the ruling
of the Tenth Circuit in Allen and hold that the district court
acted well within its discretion in excluding the testimony.
Therefore, I respectfully dissent.
