                            PUBLISHED

UNITED STATES COURT OF APPEALS
                FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,              
                 Plaintiff-Appellee,
                 v.                               No. 02-4104
MARVEL JOHNSON PRINCE-OYIBO,
             Defendant-Appellant.
                                       
           Appeal from the United States District Court
        for the Eastern District of Virginia, at Alexandria.
              Claude M. Hilton, Chief District Judge.
                           (CR-01-438)

                      Argued: January 24, 2003

                      Decided: February 27, 2003

        Before WILLIAMS and KING, Circuit Judges, and
               HAMILTON, Senior Circuit Judge.



Affirmed by published opinion. Judge King wrote the opinion, in
which Judge Williams joined. Senior Judge Hamilton wrote a dissent-
ing opinion.


                             COUNSEL

ARGUED: Matthew Alan Wartel, BYNUM & JENKINS, P.L.L.C.,
Alexandria, Virginia, for Appellant. Eric David Edmondson, Special
Assistant United States Attorney, OFFICE OF THE UNITED
STATES ATTORNEY, Alexandria, Virginia, for Appellee. ON
BRIEF: Paul J. McNulty, United States Attorney, OFFICE OF THE
UNITED STATES ATTORNEY, Alexandria, Virginia, for Appellee.
2                  UNITED STATES v. PRINCE-OYIBO
                             OPINION

KING, Circuit Judge:

   Marvel Johnson Prince-Oyibo appeals his conviction on one count
of travel document fraud. Prior to trial, the Government moved in
limine to exclude both the results of Prince-Oyibo’s polygraph exami-
nation, and evidence that he suffered persecution as a Christian in his
predominantly Muslim home country of Nigeria. During the course of
the jury trial, the district court granted both portions of the Govern-
ment’s motion, thereby excluding both the polygraph evidence and
the evidence of persecution. In his appeal, Prince-Oyibo asserts that
the evidentiary exclusions constitute reversible error. For the reasons
stated below, we disagree and affirm.

                                  I.

   Prince-Oyibo arrived at Dulles International Airport after a flight
from Lagos, Nigeria, by way of Amsterdam, on October 26, 2001. At
border control, he presented his Nigerian passport, with an enclosed
United States non-immigrant B1/B2 tourist type visa foil stamp, to
Immigration and Naturalization Service Inspector Warren Blair.
Inspector Blair had reservations concerning the authenticity of the
visa and referred Prince-Oyibo to secondary inspection for further
investigation. The secondary inspector found additional problems
with the visa and determined that it was not genuine.

   On October 29, 2001, Prince-Oyibo was arrested and was charged
by criminal complaint with travel document fraud, to wit, that he "did
knowingly use, and attempt to use, a false, forged, counterfeited and
altered nonimmigrant visa . . . knowing it to be forged, counterfeited,
altered, and falsely made," in violation of 18 U.S.C. § 1546(a). On
November 27, 2001, a grand jury in the Eastern District of Virginia
returned an indictment charging Prince-Oyibo with the same offense
as the criminal complaint.

  During Prince-Oyibo’s January 30, 2002, jury trial, the Govern-
ment presented the testimony of forensics examiner Lurline Trizna.
Examiner Trizna concluded that, while the passport was genuine and
                    UNITED STATES v. PRINCE-OYIBO                       3
unaltered and the visa was genuine when issued, various subtle abnor-
malities indicated that the visa had subsequently been altered. At the
conclusion of Examiner Trizna’s testimony, the Government intro-
duced a State Department document showing that Prince-Oyibo’s visa
foil had originally been issued to a Nigerian woman.

   At trial, Prince-Oyibo did not challenge the Government’s conten-
tion that his visa had been altered. Rather, his defense was that he
"never intended to get a fraudulent visa"; that his failure to realize the
visa had been altered was reasonable; and that his ignorance of the
proper procedure for obtaining a visa, coupled with his culture’s prac-
tice of "paying officials to do what they are supposed to do," pre-
vented him from realizing that his visa was "counterfeit, altered,
falsely made or otherwise unlawfully obtained."

   Prince-Oyibo took the witness stand at trial to explain the circum-
stances surrounding his acquisition of the visa. This, he stated, was
the first time that he had ever needed a visa. Given his inexperience,
he accepted the offer of a friend, Tony Igberi, to assist him. Igberi
travelled with Prince-Oyibo to Lagos, where they went to the United
States embassy and met a man who appeared to be an embassy
employee. The purported embassy employee had previously been
given certain documentation (Prince-Oyibo’s passport, birth certifi-
cate, and bank statements), as well as US $2,045, all of which Prince-
Oyibo had brought with him to Lagos. Prince-Oyibo completed a visa
application and departed.

   Several weeks later, Prince-Oyibo returned to the embassy on the
appointed date to receive his visa. An embassy employee handed him
both his passport and what he believed to be a legitimate visa. Prince-
Oyibo testified that he did not notice any irregularities; nor was he
made suspicious by the fact that attainment of the visa had required
the payment of such a large sum: he was inexperienced with foreign
travel, and, in Nigeria, it is common to have to "tip" officials to do
their jobs in a timely fashion. Furthermore, when Prince-Oyibo
checked with two airlines (KLM and British Airways) concerning
flights to the United States, both airlines indicated that they had con-
firmed the visa. And when the visa was checked during the Amster-
dam stopover of his KLM flight to Dulles, the visa was again
4                   UNITED STATES v. PRINCE-OYIBO
confirmed. Thus, Prince-Oyibo testified, when he presented the visa
to Inspector Blair, he believed it to be legitimate.

   Prior to trial, Prince-Oyibo had taken and passed a polygraph
examination regarding whether he knew the visa to be false, altered,
counterfeit, or forged. The test, according to the retired FBI forensic
polygrapher who administered it, indicated that Prince-Oyibo was
truthful when he stated that he did not know that the visa was illegiti-
mate. Before trial, the Government moved in limine to exclude this
opinion from evidence, citing our circuit’s per se rule that the results
of polygraph tests are inadmissible. On the day of trial, after hearing
argument on the Government’s motion to exclude Prince-Oyibo’s
polygraph evidence, the court granted the motion.

   Prince-Oyibo also hoped to present evidence showing that he was
a prominent Christian in Nigeria and that, as such, he faced persecu-
tion from his country’s Muslim majority. When asked during his
polygraph examination "Did you come to the U.S. as you were afraid
for your personal safety because of your religious beliefs?", the test
indicated that Prince-Oyibo’s affirmative answer was truthful. Prior
to trial, however, the Government had also moved in limine to
exclude all evidence relating to the defendant’s past or future persecu-
tion. At the start of Prince-Oyibo’s trial, the court withheld judgment
on the admissibility of the persecution evidence, in order to "wait and
see what you all present to see whether or not [it] becomes relevant."
Ultimately, the court found that the persecution evidence was irrele-
vant to the central issue in the case, that is, "whether [the defendant]
got a forged document and knew whether it was forged." Accord-
ingly, the court granted the Government’s motion to exclude all evi-
dence of past or future religious persecution.

   The sole issue before the jury was whether, "when the defendant
used [the] nonimmigrant visa, he knew it was counterfeit, altered,
falsely made or otherwise unlawfully obtained" and "did not act
because of ignorance, mistake, or accident."1 The jury convicted
Prince-Oyibo, and the court sentenced him to three months in prison
    1
   The trial court rejected the prosecution’s "willful blindness" instruc-
tion on the ground that there was insufficient evidence to justify such an
instruction.
                    UNITED STATES v. PRINCE-OYIBO                       5
(which amounted to time already served); two years of supervised
release; a fine of $1,000; and a special assessment of $100. Prince-
Oyibo filed a timely notice of appeal, and we possess jurisdiction pur-
suant to 28 U.S.C. § 1291.

                                   II.

   We review rulings on the admissibility of scientific evidence, such
as polygraph test results, for abuse of discretion. United States v.
Ruhe, 191 F.3d 376, 387-88 (4th Cir. 1999). In so doing, we keep in
mind that "[a] district court by definition abuses its discretion when
it makes an error of law." United States v. Stitt, 250 F.3d 878, 896
(4th Cir. 2001) (internal quotation omitted). An abuse of discretion
standard also applies to evidentiary issues such as relevancy. United
States v. Ellis, 121 F.3d 908, 926 (4th Cir. 1997).

                                   III.

                                   A.

    Prince-Oyibo first contends that the district court’s exclusion of his
polygraph evidence constitutes reversible error. Though he recognizes
that we have previously held polygraph evidence per se inadmissible,
he maintains that recent advances in polygraph testing have rendered
it sufficiently reliable for admission under the standard enunciated by
the Supreme Court in Daubert v. Merrell Dow Pharmaceuticals, Inc.,
509 U.S. 579 (1993). The error is a reversible one, he maintains,
because the polygraph test results reached the critical issue in his
case, to wit, whether he was truthful when he stated that he did not
know that his visa was false, forged, counterfeit, or altered when he
presented it for inspection.

   Prior to Daubert, this circuit consistently maintained a per se rule
that the results of an accused’s or a witness’s polygraph test are not
admissible to bolster or undermine credibility.2 See United States v.
  2
    The qualification that polygraph evidence is per se inadmissible only
if offered "to bolster or undermine credibility" becomes clear through our
pre-Daubert, Council Oil case. There, the Government had offered
6                   UNITED STATES v. PRINCE-OYIBO
Chambers, 985 F.2d 1263, 1270-71 (4th Cir. 1993); United States v.
A & S Council Oil Co., 947 F.2d 1128, 1134 (4th Cir. 1991); United
States v. Morrow, 731 F.2d 233, 238 (4th Cir. 1984) (describing poly-
graph evidence as "traditionally excluded"); see also United States v.
Porter, 821 F.2d 968, 974 (4th Cir. 1987) (holding that it is impermis-
sible even to mention that a witness has taken a polygraph test);
United States v. Tedder, 801 F.2d 1437, 1444-45 (4th Cir. 1986)
(same). Absent an en banc overruling or a superseding contrary deci-
sion of the Supreme Court, we, as a circuit panel, are bound by these
precedents. Scotts Co. v. United Indus. Corp., 315 F.3d 264, 271 n.2
(4th Cir. 2002). The questions before us, then, are two: (1) Did Dau-
bert work a change in the law governing the admissibility of expert
opinion testimony, such that the viability of per se rules barring
admission of polygraph evidence has been thrown into doubt? And,
if so, (2) have our post-Daubert precedents already resolved the mat-
ter by reestablishing this Circuit’s adherence to our longstanding per
se bar against polygraph evidence? We address these issues in turn.

                       1. The Impact of Daubert

    The Federal Rules of Evidence provide that "[i]f scientific, techni-
cal, or other specialized knowledge will assist the trier of fact to
understand the evidence or to determine a fact in issue, a witness
qualified as an expert by knowledge, skill, experience, training, or
education, may testify thereto in the form of an opinion or otherwise
. . . ." Fed. R. Evid. 702. In Daubert, the Supreme Court made clear
that it is the duty of the trial court to perform the gatekeeping function
with respect to expert testimony: "the trial judge must ensure that any
and all scientific testimony or evidence admitted is not only relevant,
but reliable." 509 U.S. at 589 (emphasis added).

expert testimony on the credibility of a key Government witness and the
trial court had refused to permit cross-examination of the expert concern-
ing the results of a polygraph test taken by the Government witness. We
held that the polygraph results should have been admitted as an attack on
the basis of the expert’s opinion, although not as a direct attack on the
credibility of the Government witness himself. United States v. A & S
Council Oil Co., 947 F.2d 1128, 1135 (4th Cir. 1991).
                    UNITED STATES v. PRINCE-OYIBO                       7
   The Daubert Court announced five factors that the trial court may
use in assessing the relevancy and reliability of proffered expert testi-
mony: (1) whether the particular scientific theory "can be (and has
been) tested"; (2) whether the theory "has been subjected to peer
review and publication"; (3) the technique’s "known or potential rate
of error"; (4) the "existence and maintenance of standards controlling
the technique’s operation"; and (5) whether the technique has
achieved "general acceptance" in the relevant scientific or expert
community. Id. at 593-94. Rather than provide a definitive or exhaus-
tive list, Daubert merely illustrates the types of factors that will "bear
on the inquiry." Id. at 593. The analysis must be "a flexible one." Id.
at 594; see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137,
141-42 (1999) (holding that testing of reliability should be flexible
and that Daubert’s five factors neither necessarily nor exclusively
apply to every expert). In short, Daubert requires that a trial court
give broad consideration to all of the various factors that may illumi-
nate the reliability of proffered expert testimony.

   Our per se bar on the admission of polygraph evidence pre-dates
Daubert. We established our rule pursuant to the "Frye test," which,
until replaced by Daubert in 1993, was for decades the dominant stan-
dard governing the admissibility of scientific evidence. See Charles
Alan Wright & Victor James Gold, 29 Federal Practice and Proce-
dure § 6266 (1997). Under Frye, scientific evidence was admissible
only if it was based on principles generally accepted as valid by the
relevant scientific community. See Frye v. United States, 293 F. 1013
(D.C. Cir. 1923). Though Daubert maintained "general acceptance"
as one of the relevant factors to weigh in the decision of whether to
admit proffered expert evidence, the Court held that the Federal Rules
of Evidence require that a district court ultimately resolve questions
of admissibility on the basis of a broader assessment of reliability.
Daubert, 509 U.S. at 589 ("Frye made ‘general acceptance’ the exclu-
sive test for admitting expert scientific testimony. That austere stan-
dard, absent from, and incompatible with, the Federal Rules of
Evidence, should not be applied in federal trials.").

   Several of our sister circuits have, in light of the 1993 Daubert
decision, reexamined the viability of their similar, pre-existing per se
rules against the admission of polygraph evidence. In particular, the
Fifth and Ninth Circuits have held that Daubert effectively overturned
8                    UNITED STATES v. PRINCE-OYIBO
their respective per se bars. Both now leave the admission or exclu-
sion of such evidence to the discretion of the district courts. See
United States v. Cordoba, 104 F.3d 225, 227-28 (9th Cir. 1997)
(remanding for district court determination of whether proffered evi-
dence was admissible under Rules 702 and 403)3; United States v.
Posado, 57 F.3d 428, 432-34 (5th Cir. 1995) (same)4; cf. United
States v. Messina, 131 F.3d 36, 42 (2d Cir. 1997) (noting, post-
Daubert, that Second Circuit has "not decided whether polygraphy
has reached a sufficient state of reliability to be admissible under Rule
702"). As the Fifth Circuit put it, "[a]fter Daubert, a per se rule is not
viable." Posado, 57 F.3d at 433.

   At the very least, by reserving the reliability assessment to the dis-
trict courts, Daubert throws into doubt the viability of our per se rule
that the results of an accused’s or a witness’s polygraph test are inad-
missible to bolster or undermine credibility. Under one possible inter-
pretation of Daubert, the court below should give Prince-Oyibo the
opportunity to present evidence in support of his claim of polygra-
phy’s newfound reliability; and, if it is satisfied that polygraphy is
indeed today reliable (a matter on which we express no opinion), that
court should be free to admit the polygraph test results in evidence.
The question remains, however, whether we, as a three-judge panel,
are free to adopt such an interpretation today. We turn to that question
now.

                      2. Our Intervening Decisions

    This circuit has, subsequent to Daubert’s announcement of the
    3
     On remand, the district court in Cordoba held that the proffered poly-
graph evidence was not admissible under Rule 702, or, alternatively, that
it was inadmissible under Rule 403. United States v. Cordoba, 991 F.
Supp. 1199, 1208 (C.D. Cal. 1998) (concluding that polygraph evidence
generally did not meet the reliability standards of Daubert, and noting
that, in any event, defects in the test at hand rendered the test inadmissi-
ble under Rule 403), aff’d, 194 F.3d 1053 (9th Cir. 1999).
   4
     After the Fifth Circuit’s remand in Posado, the district court held that
the proffered polygraph evidence was not admissible. As in Cordoba, the
district court relied, in the alternative, on Rules 702 and 403. United
States v. Ramirez, 1995 WL 918083 (S.D. Tex. Nov. 17, 1995).
                     UNITED STATES v. PRINCE-OYIBO                        9
new, multi-factored test for admissibility of expert testimony, contin-
ued to invoke its longstanding per se rule against the admission of
polygraph evidence. See Ruhe, 191 F.3d at 388 & n.9 (adhering to
"this circuit’s per se ban on polygraph evidence"); United States v.
Sanchez, 118 F.3d 192, 197 (4th Cir. 1997) ("The rule [that polygraph
evidence is never admissible to impeach the credibility of a witness]
remains . . . in this circuit . . . ."). However, in each instance, we have
also noted the change in the law effected by Daubert. In both Ruhe
and Sanchez, we suggested that it may be necessary to overturn our
longstanding per se rule against admissibility of polygraph evidence,
and that en banc consideration may not be required to do so. On the
basis of these suggestions, Prince-Oyibo contends that our post-
Daubert precedents have reserved, rather than resolved, the questions
of (1) whether Daubert requires that this Circuit change its position
on polygraph evidence, and (2) whether a mere panel is free (as pan-
els of the Fifth and Ninth Circuits found themselves to be) to
announce that change.

   Our consideration of the impact of Daubert on this Circuit’s per se
ban against polygraph evidence is traceable to a suggestion raised in
United States v. Toth, 91 F.3d 136 (4th Cir. July 31, 1996) (unpub-
lished). There, our unpublished, per curiam opinion noted the Fifth
Circuit’s decision that, due to the change in the law effected by Dau-
bert, en banc consideration was not necessary to overturn that cir-
cuit’s per se rule against admissibility of polygraph evidence.
Nonetheless, we adhered to our pre-Daubert precedents and recited
the "rule in this Circuit . . . that evidence that an accused or a witness
has taken a polygraph test is inadmissible." Id. at **4. While we sug-
gested that "we might be inclined to agree with the Fifth Circuit in
an appropriate case," we decided that it was "not necessary to reach
that issue in Toth’s case," because the trial court was within its discre-
tion in excluding the evidence under Rule 403. Id. at **5.

    A year later, in Sanchez, we returned to the Toth suggestion, noting
that "we recently suggested that it is possible to change our prohibi-
tion against polygraph evidence without the approval of the en banc
court in light of [Daubert]." 118 F.3d at 197 n.3. Nonetheless, we
held in Sanchez that "[t]he rule [against polygraph evidence] remains
. . . in this circuit, and is binding upon us in this case . . . ." 118 F.3d
at 197. "[I]n any event," we continued, "we would find any error in
10                 UNITED STATES v. PRINCE-OYIBO
excluding this evidence harmless as having no significant relevance
to any material issue going to [the defendant’s] guilt." Id.

   In Ruhe, we again took note of the Toth suggestion "that a panel
could rely upon [Daubert] to alter the circuit’s law on polygraph evi-
dence." 191 F.3d at 388 n.9. However, as in Toth itself, we adhered
in Ruhe to our per se bar, reasoning that the appellant had "not
advanced [the Toth] argument and we do not pass upon it." Id.

    Although both Ruhe and Sanchez ultimately applied the per se bar,
it is nonetheless not immediately clear that either case forecloses the
possibility that we, as a panel, might act on the Toth suggestion and
rely on the Daubert change of law to alter our circuit’s precedent on
polygraph evidence: in Ruhe, the panel did not reject the Toth sugges-
tion outright, but rather sidestepped the suggestion on the ground that
the appellant there had not raised it. By contrast, Prince-Oyibo has
advanced the Toth argument. And while Sanchez did come closer to
simply rejecting the Toth suggestion, it stopped short when it invoked,
in the alternative, the doctrine of harmless error. Again by contrast,
an error in excluding the polygraph evidence indicating that Prince-
Oyibo was telling the truth when he stated that he did not know his
visa to be false has significant relevance to a material issue going to
the defendant’s guilt.

   These distinctions notwithstanding, we conclude that, to the extent
that Daubert’s alteration of the legal landscape threw into doubt the
viability of our per se rule against polygraph evidence, Ruhe and San-
chez effectively resolved those doubts in favor of the rule. In each
case, we treated our pre-Daubert polygraph decisions as continuing
to carry precedential force. See Ruhe, 191 F.3d at 388 (holding that
"as a simple panel, we are bound by prior precedent" to adhere to the
per se ban (emphasis added)); Sanchez, 118 F.3d at 197 (holding that
the traditional rule that polygraph evidence is never admissible to
impeach the credibility of a witness "is binding upon us in this case"
(emphasis added)). In so doing, we effectively reaffirmed our per se
ban on polygraph evidence. Cf. United States v. Scheffer, 523 U.S.
303, 311 (1998) (citing our Sanchez decision for the proposition that
this circuit "has recently reaffirmed its per se ban" on polygraph evi-
dence).
                    UNITED STATES v. PRINCE-OYIBO                      11
   In sum, while we might otherwise be inclined to hold that Daubert
requires a more nuanced evaluation of polygraph evidence than that
dictated by the per se rule on which the district court relied, and that
the change in law effected by Daubert leaves a mere panel free to
acknowledge this requirement, our post-Daubert precedents foreclose
our abandonment today of this Circuit’s per se rule. Accordingly, we
conclude that only the en banc Court has the authority to consider
whether, "[a]fter Daubert, a per se rule is not viable." Posado, 57 F.3d
at 433. We affirm the district court’s exclusion — pursuant to our per
se rule, and with no Daubert inquiry into the reliability of the prof-
fered expert testimony — of the results of Prince-Oyibo’s polygraph
test.

                                   B.

   Prince-Oyibo next maintains that his religious persecution was an
important part of his defense, in that it tended to explain why he
would not question the large sum of money that he had to pay to
obtain his visa. As a result, he argues, exclusion of this evidence vio-
lated his constitutional right to present a defense. The Government
responds that the district court was within its discretion in excluding
the evidence of persecution, since the defendant’s fear of persecution
was irrelevant to whether Prince-Oyibo intended to use an altered visa
to enter the United States.

   As the Government correctly notes, a defendant’s right to present
a defense is not absolute: criminal defendants do not have a right to
present evidence that the district court, in its discretion, deems irrele-
vant or immaterial. See Taylor v. Illinois, 484 U.S. 400, 410 (1988)
("The accused does not have an unfettered [Sixth Amendment] right
to offer testimony that is incompetent, privileged, or otherwise inad-
missible under standard rules of evidence."); see also Montana v.
Egelhoff, 518 U.S. 37, 42 (1996) (applying same rule in Due Process
context).

   The only issue that the jury considered was whether Prince-Oyibo
actually knew his visa to be "counterfeit, altered, falsely made or oth-
erwise unlawfully obtained." While testimony on persecution may
have been relevant to counter the Government’s proffered "willful
blindness" instruction (and, in fact, so the defense argued), this point
12                  UNITED STATES v. PRINCE-OYIBO
of potential relevance was mooted by the court’s refusal of that
instruction. See supra note 1. Similarly, such testimony might have
been relevant in support of a duress defense; however, Prince-Oyibo
did not present such a defense. The only issue before the jury was
whether the defendant actually knew of his visa’s illegality. Since evi-
dence of Prince-Oyibo’s religious persecution does not tend to prove
his claim that he did not have actual knowledge that his visa was
false, the district court was within its discretion in excluding the evi-
dence of persecution as irrelevant.

                                  IV.

   For the foregoing reasons, the conviction of Marvel Johnson
Prince-Oyibo is affirmed.

                                                            AFFIRMED

HAMILTON, Senior Circuit Judge, dissenting:

   This circuit has never addressed the question of whether our per se
rule banning the admission of polygraph evidence to bolster or under-
mine the credibility of a witness is consistent with the principles con-
cerning the admission of scientific or technical evidence enunciated
in Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993). That
question, which is finally squarely before the court, must be answered
in the negative. For this reason, the district court should have given
Prince-Oyibo the opportunity to demonstrate that his proffered poly-
graph evidence was admissible under Daubert. Because, on the record
before the court, the exclusion of Prince-Oyibo’s proffered polygraph
evidence was not harmless error, I am constrained to conclude that
Prince-Oyibo’s 18 U.S.C. § 1546(a) conviction should be vacated and
the case should be remanded to the district court with instructions to
conduct a proper Daubert inquiry. If, on remand, the district court
concludes that Prince-Oyibo’s proffered polygraph evidence is inad-
missible, the district court would be free to reinstate the conviction.

                                    I

  The first seminal case addressing the admissibility of polygraph
evidence was Frye v. United States, 293 F. 1013 (D.C. Cir. 1923). In
                    UNITED STATES v. PRINCE-OYIBO                      13
Frye, the trial court refused to admit the results of a systolic blood
pressure test (a crude precursor to the polygraph test), which the
defendant sought to introduce in his murder trial. Id. at 1014. The
issue before the Frye court was whether the results of the systolic
blood pressure test should have been admitted into evidence. Id. The
Frye court used a "general acceptance" standard in order to determine
the admissibility of scientific or technical evidence in the context of
the science of polygraphy. Id. at 1014. The general acceptance stan-
dard required the proponent of the evidence to show that the science
was generally accepted in the relevant scientific community from
which it emerged. Id. According to the Frye Court,

     [j]ust when a scientific principle or discovery crosses the
     line between the experimental and demonstrable stages is
     difficult to define. Somewhere in this twilight zone the evi-
     dential force of the principle must be recognized, and while
     courts will go a long way in admitting expert testimony
     deduced from a well-recognized scientific principle or dis-
     covery, the thing from which the deduction is made must be
     sufficiently established to have gained general acceptance in
     the particular field in which it belongs.

Id. Because the systolic blood pressure test had "not yet gained such
standing and scientific recognition among physiological and psycho-
logical authorities as would justify the courts in admitting expert testi-
mony deduced from the discovery, development, and experiments
thus far made," evidence of its results was ruled inadmissible. Id.

   Frye became the seminal polygraph case and, consequently, over
the next five decades, virtually every state and federal court prohib-
ited the admission of polygraph evidence. See generally James R.
McCall, Misconceptions and Reevaluation-Polygraph Admissibility
After Rock and Daubert, 1996 U. Ill. L. Rev. 363, 366-70 (analyzing
Frye and its progeny). In this circuit, post-Frye and pre-Daubert, we
concluded in numerous cases that the admission of polygraph evi-
dence to bolster or undermine the credibility of a witness was per se
inadmissible. See, e.g., United States v. Chambers, 985 F.2d 1263,
1270-71 (4th Cir. 1993); United States v. A & S Council Oil Co., 947
F.2d 1128, 1134 (4th Cir. 1991); see also United States v. Porter, 821
F.2d 968, 974 (4th Cir. 1987) (holding that evidence "of a plea agree-
14                   UNITED STATES v. PRINCE-OYIBO
ment containing a provision that the government’s witness has agreed
to take a polygraph test to verify trial testimony constitutes impermis-
sible bolstering of the witness’s credibility"); United States v. Tedder,
801 F.2d 1437, 1444 (4th Cir. 1986) (holding that "evidence that the
accused or a witness has taken a polygraph test is inadmissible");
United States v. Morrow, 731 F.2d 233, 238 (4th Cir. 1984) (holding
that stipulated admission of polygraph test results was, "at most,
harmless error"); but see United States v. Webster, 639 F.2d 174, 186
(4th Cir. 1981) (holding that district court has broad discretion to
admit polygraph evidence).1
  1
    As noted by the majority, ante at 5 n.2, our per se rule only applies
to the admission of polygraph evidence offered to bolster or undermine
the credibility of a witness. Cf. A & S Council Oil Co., 947 F.2d at 1133
(holding that, where the government offered expert testimony on the
credibility of a key government witness and the district court refused to
permit cross-examination of the expert concerning the results of a poly-
graph test taken by the witness, the polygraph test results should have
been admitted as an attack on the expert’s opinion, although not as a
direct attack on the credibility of the witness). Aside from A & S Council
Oil Co., this court, other courts, and the government have expressed
approval of the use of polygraph tests in other situations. See, e.g.,
United States v. Music, 2002 WL 31387536, at *1-3 (4th Cir. 2002)
(unpublished) (upholding imposition of condition of supervised release
requiring defendant convicted of possessing child pornography to partici-
pate in mental health program that could include polygraph testing);
United States v. Queen, 2001 WL 882955, at *1 (4th Cir. 2001) (unpub-
lished) (holding that the government’s reliance, in failing to move for
downward departure for substantial assistance, on the results of a poly-
graph examination, which indicated that defendant lied about distributing
drugs while released on bond, did not amount to an unconstitutional
motive, even though such results would have been inadmissible at trial
and, thus, the district court did not err in refusing to compel the govern-
ment to file a substantial assistance motion); Bennett v. City of Grand
Prairie, Texas, 883 F.2d 400, 405-06 (5th Cir. 1989) (holding that magis-
trates may consider polygraph evidence when determining whether prob-
able cause to issue an arrest warrant exists); United States v. Lindell, 881
F.2d 1313, 1326 (5th Cir. 1989) (holding that "[i]mpeachment evidence
includes the results of a polygraph test" for purposes of the Brady rule).
Not surprisingly, at oral argument, the government acknowledged that it
frequently uses and heavily relies upon polygraph tests in a wide variety
of situations, including when deciding on whether to make a substantial
                    UNITED STATES v. PRINCE-OYIBO                      15
   In Daubert, the Supreme Court held that scientific expert testimony
is admissible under Rule 702 of the Federal Rules of Evidence2 if the
expert’s testimony is based on a reliable foundation and is relevant to
the task at hand. Daubert, 509 U.S. at 597. Daubert expressly rejected
the Frye "general acceptance" standard, holding that the Frye stan-
dard was superseded by the adoption of the Federal Rules of Evi-
dence. Daubert, 509 U.S. at 589. In its stead, the Supreme Court
outlined a flexible inquiry driven primarily by Federal Rules of Evi-
dence 401, 402, 403, and 702. After discussing the thrust of the fed-
eral rules, as reflected in Rules 401 and 402, the Court noted that
nothing in Rule 702, which governs the admissibility of expert testi-
mony, makes general acceptance an absolute prerequisite to admissi-
bility. Daubert, 509 U.S. at 588. What Rule 702 does require, the
Court held, is that the district court make initial determinations that
the proffered evidence possesses sufficient evidentiary reliability to
be admissible as scientific, technical, or other specialized knowledge
and that the proffered evidence is relevant in the sense that it will
assist the trier of fact to understand the evidence or to determine a fact
in issue. Daubert, 509 U.S. at 592-95. With regard to the reliability
and relevance determinations, the Court emphasized a number of fac-
tors, including: (1) whether the theory can be (and has been) tested;
(2) whether it has been subjected to peer review and publication; (3)
its known or potential error rate; (4) the existence and maintenance
of standards controlling its operation; and (5) whether it has attracted
wide-spread acceptance within the relevant scientific community. Id.
at 592-94. The Court also emphasized that a district court evaluating
the admission of expert testimony under Rule 702 should also con-
sider other applicable rules of evidence, including Rule 403, which
authorizes the exclusion of relevant evidence whose probative value

assistance motion on behalf of a criminal defendant to reduce his sen-
tence; nevertheless, the government stressed the need for a per se rule
banning the admission of polygraph evidence to bolster or undermine the
credibility of a witness.
  2
    Under Rule 702, a qualified expert witness may testify "in the form
of an opinion or otherwise, if (1) the testimony is based upon sufficient
facts or data, (2) the testimony is the product of reliable principles and
methods, and (3) the witness has applied the principles and methods reli-
ably to the facts of the case." Fed. R. Evid. 702.
16                  UNITED STATES v. PRINCE-OYIBO
is substantially outweighed by its danger of unfair prejudice, confu-
sion of the issues, or misleading the jury. Daubert, 509 U.S. at 595.
The emphasis behind these suggested guidelines was that the district
court had a "gatekeeping role" that was to ensure the reliability and
relevancy of the information being offered. Id. at 597. This gatekeep-
ing role was designed to give sufficient discretion to the district court
in order to avoid problems for the trier of fact. Id.

   Without question, our per se rule banning the admission of poly-
graph evidence to bolster or undermine the credibility of a witness is
inconsistent with the flexible inquiry assigned to the district court by
Daubert; indeed, the majority even impliedly recognizes this fact.
Ante at 8 ("At the very least, by reserving the reliability assessment
to the district courts, Daubert throws into doubt the viability of our
per se rule that the results of an accused’s or a witness’s polygraph
test are inadmissible to bolster or undermine credibility."). To be sure,
Daubert and the Federal Rules of Evidence recognize the gatekeeper
role of the district court, which is for the specific purpose of screening
evidence under Daubert and the Federal Rules of Evidence. A per se
rule of exclusion does not allow the district court to perform its proper
function under Daubert and the Federal Rules of Evidence. Simply
put, the proponent of polygraph evidence should be given the oppor-
tunity to demonstrate the relevance and the reliability of the evidence
before a decision on admissibility is made.

   Consistent with this analysis, numerous courts have recognized that
a per se rule banning the admission of polygraph evidence is inconsis-
tent with Daubert. See, e.g., United States v. Cordoba, 104 F.3d 225,
228 (9th Cir. 1997) (holding that Daubert overruled its per se rule
excluding all unstipulated polygraph evidence offered in civil and
criminal trials); United States v. Posado, 57 F.3d 428, 434 (5th Cir.
1995) (holding that its per se rule against the admission of polygraph
evidence in federal court not viable in light of Daubert); see also
United States v. Lea, 249 F.3d 632, 638-41 (7th Cir. 2001) (noting
that a district court’s decision on the admissibility of polygraph
results deserves considerable deference, and will be reversed only
when the district court has abused its discretion); United States v. Pic-
cinonna, 885 F.2d 1529, 1531-37 (11th Cir. 1989) (rejecting per se
rule). The rationale behind these decisions is obvious and was best
stated by the Fifth Circuit in Posado:
                     UNITED STATES v. PRINCE-OYIBO                     17
      [W]e do not now hold that polygraph examinations are sci-
      entifically valid or that they will always assist the trier of
      fact, in this or any other individual case. We merely remove
      the obstacle of the per se rule against admissibility, which
      was based on antiquated concepts about the technical ability
      of the polygraph and legal precepts that have been expressly
      overruled by the Supreme Court.

57 F.3d at 434.3

   The majority in this case feels compelled to reject Daubert
because, in the majority’s view, "our post-Daubert precedents fore-
close our abandonment . . . of this Circuit’s per se rule." Ante at 11.
However, an examination of these precedents leads inexorably to the
conclusion that this court has not addressed, let alone answered, the
question of whether our per se rule banning the admission of poly-
graph evidence to bolster or undermine the credibility of a witness is
consistent with the principles concerning the admission of scientific
or technical evidence set forth in Daubert.

   In United States v. Toth, 1996 WL 426865 (4th Cir. 1996), one of
Toth’s codefendants entered into a plea agreement, which was condi-
tioned on the codefendant’s successful completion of a polygraph
examination. Id. at *4. At Toth’s trial, the codefendant testified for
the government, but the government had earlier argued in its opening
statement that some of the codefendant’s testimony favorable to Toth
should not be believed. Toth sought to introduce evidence concerning
the codefendant’s successful completion of the polygraph examina-
tion, but the district court excluded the evidence "under Fourth Circuit
precedent" and Rule 403. Toth, 1996 WL 426865, at *4.

   On appeal, we noted that the "rule in this Circuit" is "that evidence
that an accused or a witness has taken a polygraph test is inadmissi-
ble." Id. We also recognized that our relevant circuit precedent was
decided before Daubert and that the Posado court observed that, due
  3
    Of note, the Posado court also concluded that, because of the change
in the law affected by Daubert, en banc consideration was not necessary
to overturn that circuit’s per se rule against admissibility of polygraph
evidence. Posado, 57 F.3d at 433.
18                  UNITED STATES v. PRINCE-OYIBO
to the change in the law effected by Daubert, en banc consideration
was not necessary to overturn the Fifth Circuit’s per se rule against
admissibility of polygraph evidence. Toth, 1996 WL 426865, at *4.
We also suggested that "we might be inclined to agree with the Fifth
Circuit in an appropriate case," but opined that it was "not necessary
to reach that issue in Toth’s case," because the district court acted
within its discretion in excluding the proffered polygraph evidence
under Rule 403. Toth, 1996 WL 426865, at *4. Thus, the Toth case
was not decided on the basis of the per se rule, but rather on the basis
that, even if the Daubert standard applied, the district court did not
abuse its discretion when it concluded that the proffered polygraph
evidence was inadmissible under Rule 403. Toth, 1996 WL 426865,
at *5.

   A year later, in United States v. Sanchez, 118 F.3d 192, 197 (4th
Cir. 1997), the defendant argued that the district court erred when it
refused to allow him to cross-examine a cooperating coconspirator
about the polygraph examination she had failed and that he should
have been allowed to mention the failed polygraph examination to the
jury. Id. at 197. Again, we recognized the per se rule and found that
the rule was "binding" on the court. Id. However, in a footnote, we
expressly declined to reach the question of whether our per se rule
banning the admission of polygraph evidence to bolster or undermine
the credibility of a witness was consistent with Daubert. Sanchez, 118
F.3d at 197 n.3.

   A little over two years later, in United States v. Ruhe, 191 F.3d 376
(4th Cir. 1999), the defendant argued that the district court erred when
it refused to admit the defendant’s polygraph evidence at trial. Id. at
387. In upholding the district court’s decision on appeal, we rejected
the defendant’s argument on the basis that we were bound by our cir-
cuit’s per se rule "absent contrary law from an en banc or Supreme
Court decision." Id. at 388. In reaching this conclusion, we noted that
we were declining to address the question of whether our per se rule
banning the admission of polygraph evidence to bolster or undermine
the credibility of a witness was consistent with Daubert because the
defendant did not advance that argument. Ruhe, 191 F.3d at 388 n.9.

  The above discussion makes it abundantly clear that this court has
never addressed, let alone answered, the question of whether our per
                    UNITED STATES v. PRINCE-OYIBO                    19
se rule banning the admission of polygraph evidence to bolster or
undermine the credibility of a witness is consistent with the principles
set forth in Daubert. With the issue now squarely before the court,
one must conclude, for the reasons set forth above, that our per se rule
is not consistent with the principles concerning the admission of sci-
entific or technical evidence outlined in Daubert. Moreover, en banc
consideration is not necessary to reach this result because a panel of
this court is not at liberty to ignore clear and unequivocal Supreme
Court precedent. Ruhe, 191 F.3d at 388 ("[A]s a simple panel, we are
bound by prior precedent from other panels in this circuit absent con-
trary law from an en banc or Supreme Court decision."); Posado, 57
F.3d at 433 ("Because no panel has squarely addressed the issue of
polygraph admissibility since Daubert, en banc consideration is not
required for this decision.").

   The only remaining question concerns harmless error under Rule
52(a). A district court’s evidentiary error is harmless if one can con-
clude, "‘with fair assurance, after pondering all that happened without
stripping the erroneous action from the whole, that the judgment was
not substantially swayed by the error.’" United States v. Urbanik, 801
F.2d 692, 698 (4th Cir. 1986) (quoting Kotteakos v. United States,
328 U.S. 750, 765 (1946)). In this case, as the majority acknowledges,
ante at 10, the categorical exclusion of the polygraph evidence indi-
cating that Prince-Oyibo was telling the truth when he stated that he
did not know his visa was fraudulent was relevant and material to
whether Prince-Oyibo committed an 18 U.S.C. § 1546(a) violation.
Under such circumstances, I am unable to conclude with fair assur-
ance that the judgment in this case was not substantially swayed by
the potentially erroneous exclusion of Prince-Oyibo’s polygraph evi-
dence. Urbanik, 801 F.2d at 698. Accordingly, the error in this case
is not harmless.

                                   II

   In summary, the district court should have given Prince-Oyibo the
opportunity to demonstrate that his proffered polygraph evidence was
admissible under Daubert. Because, on the record before the court,
the exclusion of Prince-Oyibo’s proffered polygraph evidence was not
harmless error, Prince-Oyibo’s 18 U.S.C. § 1546(a) conviction should
be vacated and the case should be remanded to the district court with
20                 UNITED STATES v. PRINCE-OYIBO
instructions to conduct a proper Daubert inquiry. If, on remand, the
district court concludes that Prince-Oyibo’s proffered polygraph evi-
dence is inadmissible under the principles enunciated in Daubert, the
district court would be free to reinstate the conviction.
