                     FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

ROSALINA LOPEZ-UMANZOR,                     
                      Petitioner,                   No. 03-72014
               v.
                                                    Agency No.
                                                    A75-011-140
ALBERTO R. GONZALES,* Attorney
General,                                              OPINION
                     Respondent.
                                            
          On Petition for Review of an Order of the
               Board of Immigration Appeals

                    Argued and Submitted
            January 13, 2005—Seattle, Washington

                         Filed May 6, 2005

       Before: Mary M. Schroeder, Chief Judge, and
  Alfred T. Goodwin and Susan P. Graber, Circuit Judges.

                     Opinion by Judge Graber




  *Alberto R. Gonzales is substituted for his predecessor, John Ashcroft,
as Attorney General of the United States, pursuant to Fed. R. App. P.
43(c)(2).

                                 4879
4882             LOPEZ-UMANZOR v. GONZALES


                         COUNSEL

Mara Kimmel, Catholic Social Services, for the petitioner.

James E. Grimes and Thomas K. Ragland, U.S. Department
of Justice, Civil Division, Office of Immigration Litigation,
Washington, D.C., for the respondent.

David R. Fine, Kirkpatrick & Lockhart LLP, Harrisburg,
Pennsylvania, and Gail L. Pendleton, Associate Director,
National Immigration Project of the National Lawyers Guild,
Boston, Massachusetts, for the amici curiae.


                         OPINION

GRABER, Circuit Judge:

   Petitioner Rosalina Lopez-Umanzor petitions for review of
a decision of the Board of Immigration Appeals (“BIA”) find-
ing her ineligible for cancellation of removal and denying her
request for voluntary departure. An immigration judge (“IJ”)
had found Petitioner to be ineligible for relief because there
was “reason to believe” that she had been involved in drug
trafficking, 8 U.S.C. § 1182(a)(2)(C); the IJ disbelieved her
testimony to the contrary. On appeal of the IJ’s decision, the
BIA rejected Petitioner’s due process arguments and affirmed
the IJ’s adverse credibility determination. We grant the peti-
tion for review and remand for a new hearing because the IJ
                    LOPEZ-UMANZOR v. GONZALES                       4883
refused to allow Petitioner to present relevant expert testi-
mony that bore on Petitioner’s credibility, relying instead on
his own stereotypical assumptions about domestic violence.

      FACTUAL AND PROCEDURAL BACKGROUND

   Petitioner is a native and citizen of Honduras who entered
the United States without inspection in 1989. Nine years later
the government sought her removal. Petitioner conceded
removability, but applied for cancellation of removal under 8
U.S.C. § 1229b(b)(2), a provision available to certain victims
of domestic violence.1 The IJ denied her application because
he found a “reason to believe” that Petitioner had been
involved in drug trafficking and, consequently, that she lacked
good moral character; he also concluded that her testimony
regarding domestic violence was not credible. The BIA
affirmed the IJ’s adverse credibility finding and his conclu-
sion that Petitioner was ineligible for cancellation of removal
and voluntary departure.

A.    The course of proceedings before the IJ

   In advance of her removal hearing, Petitioner submitted
evidence intended to corroborate her allegation that she had
suffered domestic violence, including medical records from
an emergency room visit and written statements from social
service providers and a psychologist who had worked with
Petitioner. The government submitted a criminal information,
charging Petitioner with Misconduct Involving a Controlled
Substance, and a notice that the charge had been dismissed.
Petitioner was the sole witness at the removal hearing on
April 1, 1999. The government presented no further evidence
and no evidence to undermine Petitioner’s testimony regard-
ing the abuse that she had endured.
  1
   Petitioner was not eligible under the general cancellation of removal
provision, 8 U.S.C. § 1229b(b)(1), because she had not been present in the
United States for ten years.
4884              LOPEZ-UMANZOR v. GONZALES
   After the April 1 removal hearing (and after missing the
deadline to file a post-hearing brief), the government submit-
ted a written statement from a detective regarding the circum-
stances surrounding the dismissed criminal charge. The
government initially sought, and was granted, a second hear-
ing to present the detective’s live testimony. Later, however,
the government twice tried to withdraw its request for a sec-
ond hearing. The IJ denied the withdrawal motions and sub-
poenaed the detective. After Petitioner’s interlocutory appeal
to the BIA was denied, the second hearing went forward, with
the IJ conducting the direct examination of the detective. Peti-
tioner did not testify at the second hearing, but made an offer
of proof and presented one character witness.

B.     Testimony regarding domestic violence

   Petitioner’s husband, Luis Calzadillas, is a lawful perma-
nent resident of the United States. Petitioner testified that, on
the night she first met Calzadillas, he drugged and raped her,
causing her to become pregnant. He assaulted her during that
pregnancy and her two others with him, including hitting her
and kicking her in the stomach. On one occasion, he caused
a miscarriage. Even when Petitioner was not pregnant, Calza-
dillas regularly hit and beat her, threw her to the ground, and
kicked her. He repeatedly threatened to call immigration
authorities if she revealed the ongoing abuse.

   When Petitioner tried to leave Calzadillas, he twice fol-
lowed her from Texas, where they had been living, to Califor-
nia, and then he followed her to Alaska. Calzadillas arrived at
Petitioner’s apartment in Anchorage. He began drinking and
attacked Petitioner with a knife, attempting to stab her in the
back, but instead hitting her hand as she turned around. She
went to an emergency room for treatment, where she told the
doctors that she had cut her hand on a broken bottle. Peti-
tioner testified that she lied about the cause of the injury
because Calzadillas had threatened to do something worse if
she did not report it that way.
                  LOPEZ-UMANZOR v. GONZALES                   4885
   After receiving treatment at the emergency room, Petitioner
returned to her apartment. She returned there because, she tes-
tified, she thought (incorrectly, as it turns out) that Calzadillas
had left, and she had nowhere else to go at the time. Later,
however, Petitioner and her two youngest daughters sought
refuge at a domestic violence shelter in Anchorage, which
provided services to her as “a survivor of domestic violence”
at the hands of Calzadillas.

   The IJ expressed doubt about whether Petitioner was telling
the truth about the abuse (a subject that we will discuss in
detail below). Nonetheless, when Petitioner offered the live
testimony of several expert witnesses who could testify on the
topic of domestic violence, and perhaps shed light on the IJ’s
credibility concerns, the IJ refused to allow them to testify.

C.   Testimony regarding drug trafficking

   While residing in Alaska, Petitioner was arrested and
charged with Misconduct Involving a Controlled Substance in
the third degree. At the time of the arrest, Petitioner was a
passenger in a car belonging to Jose Armando Gomez-
Mendoza who, she testified, was the boyfriend of her 23-year-
old daughter. Anchorage police stopped the car and arrested
both Gomez-Mendoza and Petitioner. The district attorney
later dropped the charge against Petitioner.

   At the second hearing in this case, Anchorage Detective
Bruce Edward Bryant testified that a reliable informant had
identified Petitioner as one of several people involved in the
distribution of crack cocaine. Detective Bryant had no first-
hand knowledge of Petitioner’s reported involvement in drug
transactions, however, nor did any of the other officers on the
case witness a transaction between the informant and Peti-
tioner. On the day of the arrest, according to the informant,
Gomez-Mendoza obtained a small package of cocaine from
Petitioner, who was holding it in her mouth, and sold the
package to the informant. When the car was stopped, half the
4886              LOPEZ-UMANZOR v. GONZALES
marked “buy” money was found in Gomez-Mendoza’s pocket
and half in Petitioner’s purse. Documents in her purse showed
her address to be the same as the one listed on the car’s regis-
tration, and telephone records showed several calls from
Gomez-Mendoza to Petitioner’s number (which also was her
daughter’s number). Additionally, a storage locker rented in
Petitioner’s name contained $934, three pagers, five cellular
telephones, and identity documents bearing Petitioner’s pho-
tograph but using other names.

   On the other hand, no cocaine was found on Petitioner
when she was arrested. Nor, despite a search, were any drugs
found in her apartment. At the initial hearing, Petitioner testi-
fied unequivocally that she never was involved in drug traf-
ficking. She testified that she was in the car because she had
asked Gomez-Mendoza for a ride to a shopping center. Spe-
cifically, Petitioner denied having held a package for Gomez-
Mendoza, denied having put anything in her mouth, and
denied having taken anything out of her mouth to give to any-
one.

   Following Detective Bryant’s testimony, the IJ accepted
Petitioner’s offer of proof with respect to the facts to which
she had testified at the earlier hearing: she relied on Gomez-
Mendoza for transportation; she had no involvement in
Gomez Mendoza’s drug transactions; and Gomez-Mendoza
gave her half of the “buy” money because he owed her money
for a radio that he previously had purchased from her. The
government specifically waived the opportunity to cross-
examine Petitioner.

   At the conclusion of the second hearing, a character wit-
ness, who had been Petitioner’s pastor for three years and
who knew her well, testified on Petitioner’s behalf as to her
good moral character. In the pastor’s opinion, Petitioner has
never been involved with drugs. After the pastor’s testimony,
the hearing was adjourned.
                     LOPEZ-UMANZOR v. GONZALES                       4887
          RELEVANT STATUTORY PROVISIONS

   [1] To qualify for cancellation of removal under 8 U.S.C.
§ 1229b(b)(2) (“Special rule for battered spouse or child”), a
provision added as part of the Violence Against Women Act
of 1994 (“VAWA”),2 Petitioner had to demonstrate that she
met each of the following five criteria:

        (1) that she had been “battered or subjected to
      extreme cruelty” by a spouse who is or was a United
      States citizen or lawful permanent resident;

        (2) that she had lived continuously in the United
      States for the three years preceding her application;

         (3) that she was a person of “good moral charac-
      ter” during that period;

         (4) that she is not inadmissible or deportable
      under various other specific immigration laws relat-
      ing to criminal activity, including 8 U.S.C.
      § 1182(a)(2); and

        (5) that her removal “would result in extreme
      hardship” to herself, her children, or her parents.

8 U.S.C. § 1229b(b)(2)(A)(i)-(v). If Petitioner failed to estab-
lish any one of those criteria, she is not eligible for cancella-
tion of removal under § 1229b(b)(2), even if she is a victim
of domestic violence.

   [2] The central issue in this case is whether Petitioner met
the fourth criterion—specifically, whether she demonstrated
  2
   Violent Crime Control and Law Enforcement Act of 1994, Pub. L. No.
103-322, Tit. IV (VAWA), subtit. G, § 40703, 108 Stat. 1796. After its
enactment, the statute was amended to reflect the transition in immigration
parlance from “suspension of deportation” to “cancellation of removal.”
4888                 LOPEZ-UMANZOR v. GONZALES
that she is not inadmissible under 8 U.S.C. § 1182(a)(2)(C),
which relates to involvement in illegal drug trafficking.3
Under § 1182(a)(2)(C), an alien is inadmissible if

      the . . . Attorney General knows or has reason to
      believe . . . [that the alien] is or has been an illicit
      trafficker in any controlled substance . . . or is or has
      been a knowing aider, abettor, assister, conspirator,
      or colluder with others in the illicit trafficking in any
      such controlled or listed substance or chemical, or
      endeavored to do so[.]

(Emphasis added.). Section 1182(a)(2)(C) does not require a
conviction, but only a “reason to believe” that the alien is or
has been involved in drug trafficking. Lopez-Molina v. Ash-
croft, 368 F.3d 1206, 1209 (9th Cir. 2004). If Petitioner is
inadmissible under § 1182(a)(2)(C), then she is ineligible for
cancellation of removal under 8 U.S.C. § 1229b(b)(2)(A)(iv).

       JURISDICTION AND STANDARD OF REVIEW

   We have jurisdiction to review due process challenges to
immigration proceedings. Reyes-Melendez v. INS, 342 F.3d
1001, 1006 (9th Cir. 2003). Claims of due process violations
in removal proceedings are reviewed de novo. Id.

                             DISCUSSION

   Petitioner’s eligibility for cancellation of removal focused
on one question: who was telling the truth about Petitioner’s
alleged involvement in drug trafficking, Petitioner or Detec-
tive Bryant? Had the IJ believed Petitioner’s explanation, then
  3
   As the IJ and the BIA properly noted, involvement in drug trafficking,
and presentation of false testimony regarding such involvement, also
would preclude Petitioner from establishing “good moral character” as
required by the third criterion, 8 U.S.C. § 1229b(b)(2)(A)(iii). The govern-
ment does not argue that Petitioner fails to meet the remaining three statu-
tory criteria.
                    LOPEZ-UMANZOR v. GONZALES                       4889
she would have met the statutory criteria for relief. Instead,
the IJ believed Detective Bryant, thereby rendering Petitioner
ineligible for relief.

   To answer that question, the IJ had to weigh Petitioner’s
credibility against the credibility of the detective and the cred-
ibility of the absent informant. We rarely disturb the result of
that kind of balancing. But here, the IJ’s assessment of Peti-
tioner’s credibility was skewed by prejudgment, personal
speculation, bias, and conjecture; and his refusal to allow
Petitioner to challenge those views by presenting expert testi-
mony violated Petitioner’s right to due process. We cannot
assume that the IJ would have struck the same balance had the
weighing begun on an even plane.

A.     The IJ improperly impugned Petitioner’s credibility and
       prejudged the utility of expert testimony.

  1.    Speculation and bias about Petitioner’s credibility

   The IJ stated, in his written decision, that “[e]ven before
hearing the testimony of Detective Bryant, the Court had
doubts about [Petitioner’s] credibility.”4 Specifically, the IJ
repeatedly expressed doubts about Petitioner’s account of
domestic violence. The IJ’s skepticism centered around three
key points: he doubted that Petitioner would stay with, or
return to, Calzadillas if he were abusive; he doubted that
Calzadillas would follow Petitioner if she did leave; and he
doubted that Calzadillas could find Petitioner if he did wish
to follow her.
  4
    His first doubt was that “[h]er demeanor during testimony often
sounded more like the recitation of a memorized story than a person actu-
ally recalling and reliving traumatic events.” We rejected a very similar
generalized statement, made by the very same immigration judge, as a
basis for an adverse credibility determination in Arulampalam v. Ashcroft,
353 F.3d 679, 686 (9th Cir. 2003).
4890                LOPEZ-UMANZOR v. GONZALES
   The IJ’s most intense skepticism was directed at the third
point, Calzadillas’ ability to find Petitioner. Before Petitioner
had even testified to the events in question, the IJ stated:
“[I]t’s just about impossible, if she didn’t tell him. She must
have communicated with him, otherwise, how could he have
possibly figured out where she went?” The IJ observed that
the Immigration and Naturalization Service5 (“INS”) com-
monly could not locate people against whom there were
orders of removal and wondered how, given the INS’s ability
to lose people, Calzadillas could have tracked Petitioner
down. In his written decision, the IJ regarded as “implausible”
the “amazing ability of [Petitioner’s] tormentors to locate her,
though she traveled to the far corners of this country to
escape.”

   The IJ also doubted that Calzadillas would have followed
Petitioner in the first place. During a discussion, early in the
hearing, of whether Calzadillas, who is originally from Mex-
ico, would follow Petitioner to Honduras, the IJ said:

      I mean, it’s not very persuasive that he is going to go
      back to a country, because he is so obsessed by her
      that he is going to follow her back to her country
      where . . . a foreign country where he doesn’t even
      have a right to be and probably can’t get a job, just
      so, you know, he can be close to her.

   Finally, the IJ expressed disbelief that Petitioner would stay
with an abusive partner. Petitioner explained that, during her
time with Calzadillas in Texas (while she was pregnant, and
then while she had a newborn daughter), she stayed at home
while Calzadillas worked. The IJ asked: “Well, why didn’t
  5
    The INS ceased to exist on March 1, 2003, when its functions were
transferred to the Department of Homeland Security. See Homeland
Security Act of 2002, Pub. L. No. 107-296, 116 Stat. 2135. We refer to
the agency as the INS because the hearings in this case took place before
the transfer.
                      LOPEZ-UMANZOR v. GONZALES                       4891
you escape then?” (She did, when her baby reached the age
of six months.) Petitioner also testified that she, along with
two of her children, returned to her Anchorage apartment after
being treated for stab wounds inflicted by Calzadillas because
she thought he had left and because they had nowhere else to
go. When she returned, Petitioner asked Calzadillas to leave,
but he refused. Later in the hearing, the IJ questioned whether
someone who was afraid to tell hospital personnel about her
abuse would be likely “to go back to the apartment where this
drunk is waiting” or would have the gumption to tell the
abuser to leave when she found him there. In his written deci-
sion, the IJ found it “implausible” that Petitioner would have
returned to her apartment “if there truly had been a chance
that a drunken abusive man with a knife was waiting there.”
He suggested several other destinations, including a park
bench, that would have been preferable and concluded that
Petitioner’s “willingness to return to her apartment so soon
after the alleged knifing event seriously detracted from her
credibility as to the actual events of that evening.”

   These areas of skepticism are important for two reasons.
First, they reveal the kind of speculation and bias that we have
held to be improper bases for an adverse credibility determina-
tion.6 Cf. Kaur v. Ashcroft, 379 F.3d 876, 885-87 (9th Cir.
  6
    Another area in which personal conjecture determined the course of
this proceeding, and influenced the IJ’s credibility determination, pertains
to Petitioner’s relationship with Gomez-Mendoza, who was with Peti-
tioner in the car on the day of her arrest. The IJ doubted that Gomez-
Mendoza, a man in his forties, could have been the boyfriend of Petition-
er’s daughter (who was 23 years old at the time of Petitioner’s arrest).
Indeed, their age difference was the primary reason the IJ gave for calling
Detective Bryant to testify after the government tried to withdraw its
request:
      There were aspects of [Petitioner’s] testimony which the Court
      found implausible and unpersuasive regarding the arrest, which
      the detective’s testimony might clarify. . . . Gomez-[Mendoza] is
      apparently a middle-aged man, closer to the age of the respondent
      than her daughter, yet she testified that this man was her daugh-
4892                 LOPEZ-UMANZOR v. GONZALES
2004) (reversing an adverse credibility determination in part
because the IJ speculated that India would not have issued a
passport with the name printed as “Ranjit,” but signed as
“Ranjeet,” despite the explanation from the petitioner’s coun-
sel that the spellings were interchangeable); Arulampalam v.
Ashcroft, 353 F.3d 679, 687 (9th Cir. 2003) (holding that the
IJ improperly speculated that experienced soldiers would have
been able to prevent the petitioner from bypassing check-
points on his way out of his country, as he testified that he
did); Paramasamy v. Ashcroft, 295 F.3d 1047, 1052 (9th Cir.
2002) (rejecting an IJ’s speculation about the petitioner’s
“real” economic motives for wanting to leave her country);
see also Reyes-Melendez, 342 F.3d at 1006 (holding that a
neutral judge is among the most basic of due process protec-
tions); Colmenar v. INS, 210 F.3d 967, 971 (9th Cir. 2000)
(stating that a due process violation occurs when an IJ pre-
judges a claim and fails to behave as a neutral fact-finder
interested in hearing the petitioner’s evidence).

   Second, these areas of skepticism are important because
they provide a context for the IJ’s refusal to hear expert testi-
mony, from professionals who had worked with Petitioner,
regarding the dynamics of abusive relationships. Cf. Zi Lin
Chen v. Ashcroft, 362 F.3d 611, 618 (9th Cir. 2004) (holding
that, when the petitioner had been “denied a reasonable
opportunity to explain what the IJ perceived as an inconsis-
tency in her testimony,” the “IJ’s doubt about the veracity of
her story [could not] serve as a basis for the denial of asy-
lum”).

    ter’s boyfriend. Her testimony did not have the ring of truth on
    this point . . . . If he is actually [Petitioner’s] boyfriend, it would
    indicate that she lacked credibility, and would affect the merits
    of her claim as an allegedly abused person.
No evidence, including Detective Bryant’s testimony, contradicted Peti-
tioner’s assertion that Gomez-Mendoza was her daughter’s boyfriend; and
their 20-year age difference is not so unusual that the IJ properly could
have discounted the accuracy of Petitioner’s testimony.
                    LOPEZ-UMANZOR v. GONZALES                   4893
  2.     Doubts about the utility of expert testimony

   The IJ was of the preconceived view that expert testimony
could do no more than repeat, uncritically, the victim’s
consistent—but potentially fabricated— story. (“You know, I
mean, she talked to [Petitioner] and believes the story, basi-
cally, so you know, it’s kind of bootstrapping then.”) Indeed,
the IJ observed that persons in need of services can be moti-
vated to fabricate stories of domestic violence:

       But . . . the more she tells these stories, the more
       benefit she accrues from all of these agencies that
       are quite eager to help her in any way they can. And
       the more they hear, the more they [p]ile on the ser-
       vices. So there’s always the possibility of someone
       embellishing in order to gain the kind of support. I’m
       not saying I don’t believe her. Don’t get me wrong.

Cf. Sanchez-Cruz v. INS, 255 F.3d 775, 779-80 (9th Cir.
2001) (observing that the IJ had focused with disapproval on
the fact that the petitioner had received welfare). And, as for
the experts’ ability to discriminate between actual victims of
domestic violence and people whose need flows from other
sources, the IJ opined:

       [T]his type of people, they don’t throw people out on
       the street. If someone comes in and says that they
       have been abused, if — if everything they observe in
       talking to them, hearing their case history is consis-
       tent with their story, they’ll basically believe it.

   Petitioner’s counsel countered that the experts’ live testi-
mony could provide information relevant to the IJ’s most crit-
ical areas of doubt, such as Calzadillas’ desire and ability to
follow Petitioner. Counsel also offered to question the experts
regarding the intake criteria they use to determine whether
someone has, in fact, been abused. She pointed out that none
4894                 LOPEZ-UMANZOR v. GONZALES
of those issues had been addressed in the written materials
previously provided by way of affidavits.

   The IJ ultimately refused the live testimony, asserting that
time was short: “I don’t — I don’t believe that I want to hear
any testimony from the experts, because — mainly because of
the lateness of the hour. If — you know, if we had more time,
perhaps, but it is 4:30 and I don’t think we could accomplish
much in 30 minutes.” The IJ assured Petitioner’s counsel that
he would consider the experts’ written materials.

B.     The IJ’s refusal to hear testimony from Petitioner’s
       experts violated due process.

   [3] Due process principles prohibit an IJ from declining to
hear relevant testimony because of a prejudgment about the
witness’s “credibility or the probative value of [the] testimo-
ny.” Kaur v. Ashcroft, 388 F.3d 734, 737 (9th Cir. 2004). “We
will grant a petition for review from a BIA decision on due
process grounds if the proceeding was so fundamentally
unfair that the alien was prevented from reasonably presenting
[his or her] case.” Reyes-Melendez, 342 F.3d at 1006 (internal
quotation marks omitted).7 Whether the IJ’s actions prevented
the introduction of significant testimony is critical to the ulti-
mate question whether the alien had a reasonable opportunity
to present evidence. See, e.g., Sanchez-Cruz, 255 F.3d at 779
(noting that the IJ “refused to allow the petitioner to introduce
evidence that specifically contradicted some of his factual
findings”); Colmenar, 210 F.3d at 971 (noting that the IJ cut
off the alien’s testimony regarding the possible political moti-
vations of the attack against him).

  In Kaur, an asylum seeker attempted to call her son, who
had been granted asylum a year earlier, as a witness to the
events that had caused her to leave her native country. The IJ
  7
   As we will discuss in the next section, “[t]he alien must also show prej-
udice.” Reyes-Melendez, 342 F.3d at 1006.
                     LOPEZ-UMANZOR v. GONZALES                        4895
refused to hear his testimony because the son had been only
8 or 9 years old at the time of the relevant incidents. 388 F.3d
at 736. The IJ then denied asylum, in part because of the
absence of corroborative evidence. Id. We held that “[t]he IJ
was not entitled to prejudge [the son’s] credibility or the pro-
bative value of his testimony.” Id. at 737. The testimony, for
which there was no substitute, was relevant to corroborate the
petitioner’s testimony and to bolster her credibility. Id.

   [4] In the circumstances of this proceeding, the IJ’s refusal
to hear testimony from Petitioner’s experts likewise violated
due process. In Kaur, of course, there was no substitute for
the son’s testimony, and the IJ there gave no reason for
excluding the testimony other than a prejudgment of its value.
See id. Here, the IJ gave two facially neutral reasons—
efficiency and the superiority of written materials—for refus-
ing the expert testimony. But the latter reason cannot suffice
when the proffered testimony was not covered in the written
materials and when it would have reflected directly on Peti-
tioner’s credibility, on specific points as to which the IJ
repeatedly had expressed skepticism. And the IJ’s claimed
interest in efficiency was belied by the substantial amount of
time the IJ spent arguing with Petitioner’s counsel about
whether to hear the testimony and by his willingness (indeed,
insistence) to call, and to hold an additional hearing to receive
testimony from, Detective Bryant.8
   8
     The IJ’s statements suggested that less neutral reasons also influenced
his decision. In his discussion with Petitioner’s counsel, the IJ appeared
to discount the value of information about typical patterns of domestic
violence as an aid in resolving inconsistencies and determining credibility
in general:
    Well, we can figure that out, you know, that someone has to have
    an explanation as to why there is something inconsistent in the
    documentary evidence. . . . I mean, the type of thinking that you
    are projecting here would account for someone who nothing ever
    happened to them being eligible for this kind of relief. Well, it
    doesn’t matter what they told the emergency room[,] they were
    afraid, you know.
4896                LOPEZ-UMANZOR v. GONZALES
   [5] Petitioner was denied an opportunity to challenge the
IJ’s preconceived views that experts in the patterns of domes-
tic violence could do no more than repeat, uncritically, the
victim’s testimony, and that evidence of such patterns was not
a helpful supplement to the traditional tools for evaluating
credibility. As we wrote in a slightly different context:

      [I]n enacting VAWA, Congress recognized that lay
      understandings of domestic violence are frequently
      comprised of “myths, misconceptions, and victim
      blaming attitudes,” and that background information
      regarding domestic violence may be crucial in order
      to understand its essential characteristics and mani-
      festations.

Hernandez v. Ashcroft, 345 F.3d 824, 836 (9th Cir. 2003)
(quoting H.R. Rep. No. 103-395, at 24 (1993)).9 In VAWA,
Congress took steps to provide judges with training on the
topics of rape and domestic violence. See Pub. L. No. 103-
322, tit. IV, subtit. D, §§ 40411-40422. In support of that
measure, Congress noted that “[a] judge who is confident in
controlling his or her own life and circumstances . . . may find
it difficult to understand the circumstances and responses of
a battered woman.” S. Rep. No. 103-138, at 46 (1993).

      Some judges and court personnel approach domestic
      violence cases, whether consciously or uncon-
      sciously, with assumptions based not on personal
      experience or the facts of a particular case but on ste-
      reotypes and biases. Judges and court personnel may
      also lack information about the psychological, eco-
      nomic, and social realities of domestic violence vic-
      tims.
  9
   In Hernandez, we were reviewing the agency’s determination that the
petitioner had not established the “extreme cruelty” requirement for sus-
pension of deportation. 345 F.3d at 832-33.
                  LOPEZ-UMANZOR v. GONZALES                  4897
Id. Congress, in other words, recognized that information
about the dynamics of abusive relationships could help adju-
dicators evaluate facts more fairly. This recognition supports
our conclusion that due process required the IJ to allow Peti-
tioner to confront his overt skepticism with expert testimony
on the issue of domestic violence.

C.   Petitioner suffered prejudice as a result of this due pro-
     cess violation and the IJ’s improper speculation as to her
     credibility.

   [6] For us to grant the petition for review on due process
grounds, Petitioner must show prejudice, “which means that
the outcome of the proceeding may have been affected by the
alleged violation.” Reyes-Melendez, 342 F.3d at 1006 (empha-
sis added). The government argues that there is no prejudice
because substantial evidence supports the IJ’s finding that
Petitioner was involved in drug trafficking, regardless of any
mistakes the IJ may have made in evaluating the credibility of
her testimony about domestic violence. That is, even if the
IJ’s improper assessment of Petitioner’s credibility resulted in
an incorrect conclusion as to her testimony about domestic
violence, it did not affect his decision to credit the detective’s
testimony over Petitioner’s with regard to the alleged drug
transaction. We do not agree.

   Petitioner and Detective Bryant presented conflicting testi-
mony with regard to the alleged drug transaction. To review:
In the initial hearing, Petitioner testified to her version of the
events leading to her arrest, in which she was an innocent
bystander. At the second hearing, Detective Bryant presented
another version, relayed from an informant, in which Peti-
tioner had held a rock of cocaine in her mouth, passed it to
Gomez-Mendoza, and received half of the marked “buy”
money in exchange. After Detective Bryant testified, in rebut-
tal Petitioner’s counsel gave a detailed offer of proof to sup-
plement Petitioner’s earlier testimony. The offer of proof
unequivocally denied any involvement in drug trafficking;
4898              LOPEZ-UMANZOR v. GONZALES
said that Petitioner needed a ride with her daughter’s boy-
friend because she lacked other transportation; and explained
the presence of the money in her purse as payment for a radio,
sold earlier to the boyfriend. Her previous testimony had
included denial of specific charges (like holding cocaine in
her mouth). The IJ accepted the offer of proof in lieu of Peti-
tioner’s live rebuttal testimony, and the government waived
the right to cross-examine.

   [7] The IJ’s decision to believe Detective Bryant over Peti-
tioner controlled the outcome of the proceeding. Our task is
to determine whether the IJ’s assessment of Petitioner’s credi-
bility regarding domestic violence, and his refusal to admit
testimony that would have challenged his preconceived view
of her credibility on that point, may have affected his resolu-
tion of the drug-related credibility dispute. On this record, we
cannot conclude that the two issues were unconnected. The
IJ’s improper prejudgment on the first issue, which culmi-
nated in his refusal to hear testimony that might have bol-
stered Petitioner’s credibility, infected his decision to believe
Detective Bryant’s testimony over Petitioner’s. Our law has
long recognized that a person who is deemed unbelievable as
to one material fact may be disbelieved in all other respects.
See Hattem v. United States, 283 F.2d 339, 343 (9th Cir.
1960) (approving, as a correct statement of the law, a jury
instruction stating that, “[i]f you find that any witness in this
trial has wilfully testified falsely as to any material fact in the
case, then you are at liberty wholly to disregard all of the tes-
timony of that witness”); Shelton v. United States, 169 F.2d
665, 667 (D.C. Cir. 1948) (discussing the maxim “falsus in
uno, falsus in omnibus”). Petitioner’s testimony regarding
domestic violence came before the testimony regarding her
arrest, and the IJ expressly stated that his credibility concerns
began during the former. “Even before hearing the testimony
of Detective Bryant,” the IJ stated in his decision, he “had
doubts about [Petitioner’s] credibility.”

   Of course, we cannot be sure that the IJ would have
reached a different conclusion about the drug transaction had
                      LOPEZ-UMANZOR v. GONZALES                           4899
he begun with a more neutral view of Petitioner’s credibility.
But our cases do not require absolute certainty. See, e.g.,
Agyeman v. INS, 296 F.3d 871, 884 (9th Cir. 2002)
(“Prejudice is shown if the violation potentially . . . affects the
outcome of the proceedings.” (internal quotation marks omit-
ted)). In this proceeding, everything came down to resolving
a conflict in testimony; and the IJ’s earlier-developed,
improperly negative view of Petitioner’s credibility may have
affected his later conclusion that it was Petitioner, not the
detective (or the informant), who lied about the drug transac-
tion. That conclusion, as we have said, controlled the out-
come.

   [8] Today’s decision by no means refutes the self-evident
proposition that one can be both a victim of domestic violence
and a drug trafficker. If the agency properly concludes that
there is reason to believe an alien is a drug trafficker,10 then
the alien is ineligible for cancellation of removal under 8
U.S.C. § 1229b(b)(2), period. But, before reaching that con-
clusion, the agency must give the alien a fair hearing in front
of a neutral decision-maker. Because the IJ’s disbelief of Peti-
tioner rested on personal speculation, bias, conjecture, and
prejudgment, and because he refused to hear testimony that
would have challenged those assumptions, we decline to
assume that a fair and neutral balancing of the conflicting tes-
timony occurred or to assume that a fair and neutral balancing
necessarily would have yielded the same answer. Thus, we
conclude that Petitioner has demonstrated prejudice.

   [9] We do not suggest that the agency was or is required to
credit Petitioner’s version of events uncritically. We merely
hold that the IJ was required to hear testimony from Petition-
er’s experts in the subject of domestic violence, as to matters
  10
    “The appropriate way of measuring whether the IJ and BIA had ‘rea-
son to believe’ ” that a petitioner is involved in drug trafficking is to assess
“whether substantial evidence supports such a conclusion.” Alarcon-
Serrano v. INS, 220 F.3d 1116, 1119 (9th Cir. 2000).
4900                LOPEZ-UMANZOR v. GONZALES
pertaining to her credibility. Thus, we remand for a new hear-
ing, to ensure that Petitioner has a full and fair opportunity to
establish her credibility, Kaur, 388 F.3d at 738 (remanding for
a new hearing), and we suggest that the new hearing be held
before a different immigration judge, Perez-Lastor v. INS,
208 F.3d 773, 783 (9th Cir. 2000).11

  PETITION GRANTED; REMANDED with instructions.




  11
    Because we remand for a new hearing on the ground discussed, we
need not and do not reach Petitioner’s other arguments about the proce-
dures below.
