                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                No. 11-30120
               Plaintiff-Appellant,
                                             D.C. No.
               v.
                                         3:10-cr-00069-
JENNIFER ANNE THOMS; TRACE RAE             JWS-JDR-1
THOMS,
                                            OPINION
            Defendants-Appellees.
                                      
       Appeal from the United States District Court
                for the District of Alaska
       John W. Sedwick, District Judge, Presiding

                 Argued and Submitted
            May 10, 2012—Seattle, Washington

                    Filed June 29, 2012

Before: Ronald M. Gould, Jay S. Bybee, and Carlos T. Bea,
                    Circuit Judges.

                   Opinion by Judge Bea




                           7693
                  UNITED STATES v. THOMS              7695




                       COUNSEL

Kirby Heller (argued), United States Department of Justice,
Appellate Section, Criminal Division, Washington, D.C.; Jo
7696                UNITED STATES v. THOMS
Ann Farrington and Stephan A. Collins, United States Depart-
ment of Justice, Office of the United States Attorney, Anchor-
age, Alaska, for the plaintiff-appellant.

George J. Dozier, Jr. (argued) and Rex Lamont Butler, Rex
Lamont Butler and Associates, Anchorage, Alaska, for
defendant-appellee Trace Thoms.

Vikram N. Chaobal, Law Office of Vikram N. Chaobal,
Anchorage, Alaska, for defendant-appellee Jennifer Thoms.


                          OPINION

BEA, Circuit Judge:

   In a criminal pre-trial matter, it is well established in our
circuit and in most others that, if a district judge is inclined
to depart from credibility findings of a magistrate judge that
were favorable to the defendant, he may only do so after hold-
ing a de novo evidentiary hearing. See United States v. Ridg-
way, 300 F.3d 1153 (9th Cir. 2002). This right is grounded in
the Due Process Clause. Id. at 1155-56.

   But what about the reverse? What if a magistrate judge rec-
ommends denying a motion to suppress, but the district judge
wishes to reverse that determination because he is inclined to
disbelieve the testimony of government officials? In that case,
must he hold a de novo hearing for the benefit of the govern-
ment, which is the plaintiff in a criminal case?

   This appeal considers such a case, and our circuit has yet
to address this question. The government primarily urges us
to adopt a broad rule: the government’s right to a de novo
hearing before a district judge is identical to that of defen-
dants, even though the government cannot directly invoke the
protections of the Due Process Clause. The defendants
                         UNITED STATES v. THOMS                           7697
counter that, without the Due Process Clause to ground this
right, the decision to hold a de novo hearing in such cases is
entirely within the district judge’s discretion.

   We disagree with both of those categorical options, and
today we adopt a middle ground, though our rule counsels
strongly in favor of holding a de novo hearing. We agree with
the defendants that the government does not have an unquali-
fied right to a de novo evidentiary hearing whenever a district
judge reverses a magistrate judge’s credibility determinations
in a way adverse to the government. But we also agree with
the government that its interest in the integrity and accuracy
of judicial proceedings—which, after all, similarly underlie a
defendant’s due process rights to such a de novo hearing—
will often counsel in favor of such a hearing. Thus, we hold
that a district court abuses its discretion when it reverses a
magistrate judge’s credibility determinations, made after
receiving live testimony and favorable to the government,
without viewing key demeanor evidence, with one exception:
where the district judge finds that the magistrate judge’s cred-
ibility determinations had no legally sufficient evidentiary
basis, so that, were they jury determinations, judgment as a
matter of law would issue for the defendant.1

                                       I.

  Although the government’s appeal challenges only the pro-
cedure by which the district court rejected the credibility
determinations of the magistrate judge, and not the merits of
  1
    By using the term “judgment as a matter of law,” we mean to incorpo-
rate the general standards of Federal Rule of Civil Procedure 50(a)(1),
which states: “If a party has been fully heard on an issue during a jury trial
and the court finds that a reasonable jury would not have a legally suffi-
cient evidentiary basis to find for the party on that issue, the court may . . .
resolve the issue against the party.” We recognize that the analogy is not
perfect, as juries do not decide the pre-trial motions which we address
here, but the value of importing that standard to this context is that it is
a standard with which district courts will be quite familiar.
7698                UNITED STATES v. THOMS
the district court’s decision to suppress the evidence, some
understanding of the events leading to this dispute is neces-
sary.

                               A.

   On February 22, 2010, an Alaska state judge issued a war-
rant to search a residential house and outbuildings located in
Wasilla, Alaska. The property is owned by defendants Trace
and Jennifer Thoms. The warrant was issued on the basis of
an affidavit submitted by Investigator Kyle Young, an Alaska
state trooper, whose affidavit provided probable cause for the
judge to conclude that the property’s owners could be grow-
ing marijuana on the property.

   The affidavit contained a variety of facts in support of the
warrant, but, for purposes of this appeal, the key piece of
information was Investigator Young’s claim that overnight on
February 21-22, 2010, he “smelled a strong odor of cultivat-
ing marijuana while driving on West Scarlett Circle, off of
Scarlett Drive in Wasilla.” He then said that “I immediately
stopped my vehicle and checked the wind direction and noted
that I was downwind of the first residence on the right on
West Scarlett Circle, off of Scarlett Drive.” Investigator
Young parked his car and walked on the roadway a short dis-
tance, and he continued to smell marijuana. In the affidavit,
he concluded that “Based upon the odor of marijuana in the
proximity of the suspect residence and the wind direction at
the time, I believe that the source of the odor was the first res-
idence on the right on Scarlett Circle, described above.”
Investigator Young later estimated that he was approximately
400 to 600 feet away from the odor’s source when he first
smelled the marijuana.

  The state court judge approved the warrant, and officers
soon executed it and searched the property. There, in two out-
buildings, police found a large marijuana grow operation,
consisting of around 400 plants. Later, co-defendant Trace
                    UNITED STATES v. THOMS                 7699
Thoms testified to the many measures he took to contain the
smell emanating from the building with the growing plants.
This included insulating and taping the garage doors, install-
ing two filtration systems, and even “ma[king] a conscious
effort to grow marijuana that was less odorous.” Thoms
expressed confidence that these protections would shield his
operation from law enforcement. “So were you able to sleep
at night knowing you had these filtration systems?” asked the
prosecutor. “I slept great,” Thoms replied.

                              B.

   Nonetheless, on July 23, 2010, the Thomses were indicted
on federal drug charges in the District of Alaska. The super-
seding indictment charged the Thomses with one count of
conspiracy to manufacture marijuana; one count of manufac-
turing marijuana; one count of maintaining a place for the
manufacture of marijuana; one count of conspiracy to commit
money laundering; and fourteen counts of money laundering.
The superseding indictment also contains allegations of crimi-
nal forfeiture against some of Thomses property and posses-
sions.

   The Thomses moved to suppress the evidence of the search,
and they requested a Franks hearing to challenge the truth of
the statements in Investigator Young’s affidavit. Under
Franks v. Delaware, 438 U.S. 154 (1978), and its progeny, a
defendant can challenge the truth of police statements con-
tained in an affidavit in support of a search warrant. Under
Franks, suppression is appropriate only where a defendant
proves that “that the magistrate or judge in issuing the warrant
was misled by information in the affidavit that the affiant
knew was false or would have known was false except for his
reckless disregard of the truth.” United States v. Stanert, 762
F.2d 775, 780 (9th Cir. 1985). Thus, to prevail on this claim,
the Thomses were required to show that Investigator Young’s
statements in the affidavit were deliberate or reckless false-
7700                   UNITED STATES v. THOMS
hoods. The matter was referred to a magistrate judge, who
granted the request to hold a Franks hearing.

   At the hearing, ten witnesses testified over the course of
two days. Seven witnesses testified on behalf of the Thomses,
including Trace Thoms and Professor Richard Doty, the
director of the Smell and Taste Center at the University of
Pennsylvania School of Medicine. Three witnesses testified
on behalf of the government: Investigator Young, and two
other officers involved in the search.

   In a detailed report and recommendation, the magistrate
“conclude[d] that the testimony at the Franks hearing does
not show recklessness by Inv. Young nor does it prove the
officer perjured himself when he claimed he smelled marijua-
na.” The magistrate therefore recommended denying the
motion to suppress.

   The Thomses filed objections to the magistrate’s report,
and the district court reversed the magistrate’s recommenda-
tion and granted the motion to suppress. The district court did
so without holding a de novo evidentiary hearing to hear any
live testimony. Instead, the district court conducted a de novo
review of the facts and the law based on the entire record,2
including the hearing transcript, and the district court con-
cluded that a preponderance of the evidence at the Franks
hearing showed that Investigator Young’s claim that he
smelled marijuana from his location was not credible. The
court said:

      To conclude that Investigator Young did smell mari-
      juana from the road, while in his vehicle would
      require the court to assume that Thoms’ filtration
  2
   As discussed further infra, 28 U.S.C. § 636(b) specifies that a district
judge “shall make a de novo determination of those portions of the report
or specified proposed findings or recommendations to which objection is
made.”
                       UNITED STATES v. THOMS                      7701
      system was either saturated or not functional; that
      the odor of marijuana left the outbuilding unfiltered
      and remained warm long enough to stay above the
      vegetation behind the Thomses’ house;[3] that it
      either traveled around the Thomses’ two-story resi-
      dence or stayed warm long enough to traverse above
      it then suddenly dropped in the area Young claimed
      to smell marijuana; and that it followed the described
      450 foot course without dispersing beyond percepti-
      ble levels. Those assumptions are contrary to a pre-
      ponderance of the evidence presented at the Franks
      hearing.

Because a “district court must suppress evidence seized under
a warrant when an affiant has knowingly or recklessly
included false information in the affidavit,” United States v.
Dozier, 844 F.2d 701, 705 (9th Cir. 1988) (emphasis added),
and the good faith exception did not apply, the district court
granted the motion to suppress.

                                   C.

   The government filed a motion to reconsider. The govern-
ment requested reconsideration solely on procedural grounds.
Namely, the government contended that the district court was
required to conduct a de novo evidentiary hearing before
rejecting the magistrate’s credibility determinations.

   The district court denied the government’s motion. The dis-
trict court acknowledged that when a district court reverses a
magistrate judge’s credibility findings in a manner adverse to
a defendant, a de novo hearing is required on due process
grounds. But “[b]ecause a defendant’s due process rights are
not at issue when a motion to suppress is granted over a mag-
istrate judge’s recommendation, a de novo evidentiary hearing
  3
   The record shows that the outbuilding is set back from the street, and
that between the street and the outbuilding there are many trees.
7702                UNITED STATES v. THOMS
is not necessarily required.” The district court noted that it
had reviewed de novo the entire record and “explained at
length how the evidence presented renders it highly improba-
ble (indeed, it seems to this court in light of all the evidence,
virtually impossible) that Investigator Young could smell the
marijuana grow under the circumstances that existed at the
time.” Moreover, “[t]hat conclusion would not change simply
because this court heard the evidence all over again.”

  The government timely appealed the district court’s orders
denying reconsideration and granting the motion to suppress.

                               II.

   We have jurisdiction to review this interlocutory appeal
from a district court’s grant of a motion to suppress under 18
U.S.C. § 3731. Whether the government has a legal right to
a de novo hearing is a question of law, and we review ques-
tions of law de novo. See Movsesian v. Victoria Versicherung
AG, 670 F.3d 1067, 1071 (9th Cir. 2012) (en banc).

                              III.

   The sole question presented is under what circumstances, if
any, a district judge may reject a magistrate judge’s credibility
finding without holding a new hearing, when the magistrate
recommends denying a motion to suppress and the district
court refuses to adopt the recommendation and grants the
motion to suppress. In resolving this question, we first address
the government’s argument that precedent requires a district
court to hold a new hearing in all such circumstances. We dis-
agree with this categorical proposition. However, we may also
look to our supervisory authority and inquire whether a more
limited rule suggesting a de novo hearing in many circum-
stances would be “desirable from the viewpoint of sound judi-
cial practice although in nowise commanded by statute or by
the Constitution.” Thomas v. Arn, 474 U.S. 140, 146-47
(1985) (emphasis added) (internal quotation marks omitted).
                    UNITED STATES v. THOMS                    7703
We conclude that such a rule is desirable. Thus, we vacate the
district court’s suppression and reconsideration orders and
remand to reconsider the issue with the new rule in mind.

                               A.

  [1] The relevant section of the Federal Magistrates Act, 28
U.S.C. § 636(b)(1), allows a magistrate judge to conduct an
evidentiary hearing on a motion to suppress and make recom-
mendations to a district judge. Then,

    Within fourteen days after being served with a copy
    [of the magistrate’s report], any party may serve and
    file written objections to such proposed findings and
    recommendations as provided by rules of court. A
    judge of the court shall make a de novo determina-
    tion of those portions of the report or specified pro-
    posed findings or recommendations to which
    objection is made. A judge of the court may accept,
    reject, or modify, in whole or in part, the findings or
    recommendations made by the magistrate judge. The
    judge may also receive further evidence or recommit
    the matter to the magistrate judge with instructions.

Id. The Supreme Court has said that it is “clear” from this text
that “the statute calls for a de novo determination, not a de
novo hearing.” United States v. Raddatz, 447 U.S. 667, 674
(1980). Thus, it is undisputed the government has no right
under the statute to require the district judge to hold a de novo
hearing when he “accept[s], reject[s], or modif[ies]” the mag-
istrate’s recommendation.

   [2] But despite the broad language of the statute, the dis-
trict court’s discretion either to hold or refuse to hold a new
hearing when considering a magistrate’s recommendation is
not unbounded. Rather, this court has said that “a district
court errs when it does not conduct a de novo evidentiary
hearing if it rejects the credibility finding of a magistrate
7704                    UNITED STATES v. THOMS
judge who recommends the granting of a motion to suppress.”
Ridgway, 300 F.3d at 1157 (emphasis added). The critical
question, then, is the source of law for the categorical rule for
which the government advocates here. If the Ridgway rule is
based solely upon a defendant’s due process rights, then it is
an asymmetrical right because, as the government admits,
“the government does not share a defendant’s right to due pro-
cess.”4 But if that right inheres in all litigants’ right to the “in-
tegrity and accuracy of the fact-finding process,” United
States v. Bergera, 512 F.2d 391, 393 (9th Cir. 1975), then the
logic requiring a de novo hearing for defendants necessarily
is symmetrical and requires a district court to conduct a de
novo hearing whenever it rejects a magistrate’s credibility
findings.

   A careful reading of our caselaw formally grounds this
right in the Due Process Clause, and therefore the government
does not have a categorical right to a de novo hearing when-
ever a district judge disagrees with a magistrate judge’s credi-
bility determinations and accompanying recommendation that
a motion to suppress be denied. However, as we note below
in subsection B, the interests recognized in these due process
cases are shared by all litigants. Thus, a similar but more lim-
ited rule is appropriate for this case.

   United States v. Bergera, the case on which the government
most heavily relies, is the earliest in the key trio of cases in
this area. In Bergera, the defendants were indicted for posses-
sion with intent to distribute marijuana after police found
  4
    The Due Process Clause of the Fifth Amendment states that “[n]o per-
son shall be . . . deprived of life, liberty, or property without due process
of law.” U.S. Const. amend. V; see also id. amend. XIV (“[N]or shall any
State deprive any person of life, liberty, or property, without due process
of law . . . .”). The Supreme Court has stated that “[t]he word ‘person’ in
the context of the Due Process Clause of the Fifth Amendment cannot, by
any reasonable mode of interpretation, be expanded to encompass the
States of the Union.” South Carolina v. Katzenbach, 383 U.S. 301, 323
(1966).
                   UNITED STATES v. THOMS                     7705
drugs in the defendants’ garage, bedroom, closets, kitchen,
and Volkswagen bus. 512 F.2d at 392. The defendants moved
to suppress the marijuana from admission into evidence, and
the matter was referred to a magistrate for an evidentiary
hearing. Id. After the hearing, the magistrate recommended
granting the motion, but, without holding a new hearing, the
district court reversed. Id.

  We reversed. We explained our rationale not in terms of
due process but in terms of the integrity and accuracy of the
judicial process generally:

    Since the magistrate sees and hears the evidence, the
    district court is entitled to rely upon his recommen-
    dations when making its decision on the motion. If,
    however, the district court chooses to reject the rec-
    ommendation of the magistrate, it must itself hear
    the testimony and see the evidence before deciding
    the motion. Permitting the district court to simply
    review dry records or listen to tape recordings of the
    evidentiary hearing conducted by the magistrate
    would not satisfy the high standard which must be
    set for factual determinations which by themselves
    can decide the outcome of a criminal trial. The
    defendant is entitled to the assurance that important
    factual conclusions will be drawn from the testimony
    and other evidence itself. That assurance is provided
    if the district court decides the motion in accordance
    with the recommendations of a judicial officer who
    observed the evidence. It is certainly provided if the
    district court sees and hears the evidence itself. But
    it is just as certainly absent if the district court is
    allowed to disregard the recommendation of the
    magistrate and decide the motion only on the basis
    of dry records and one dimensional tapes. Therefore
    we hold that the district court erred when it set aside
    the magistrate’s recommendation and ruled on the
7706                     UNITED STATES v. THOMS
      motion to suppress without hearing the evidence on
      the motion itself.

Id. at 394. Were Bergera that last word on this topic, we
could conclude that the right to a full de novo hearing is
entirely symmetrical. Bergera’s concern with the “integrity
and accuracy of the fact-finding process” generally applies to
all who have a stake in the judicial process. Id. at 393. But
later decisions require us to recognize that its scope is limited.5

   Five years after Bergera, the Supreme Court decided
United States v. Raddatz. In Raddatz, the defendant was
indicted for unlawfully receiving firearms, and he moved to
suppress incriminating statements he made to federal agents.
447 U.S. at 669-70. The matter was referred to a magistrate,
and both the defendant and the agents testified at a hearing.
Id. at 670-71. The magistrate recommended denying the
motion to suppress, and the district court accepted the recom-
mendation and denied the motion to suppress without holding
a de novo hearing. Id. at 672. The defendant raised two con-
tentions before the Supreme Court: first, that the Federal
Magistrates Act, newly amended in 1976, required a de novo
hearing, and, second, that the Due Process Clause requires a
de novo hearing.6 Id. at 673, 677. The Court rejected both
claims. Id. at 676, 683-84. Raddatz’s interpretation of § 636,
the relevant portions of which have not been amended since
then, precludes the government from contending here that it
  5
     Further, at the time of Bergera, the version of § 636 then in force was
broader, as it allowed district courts to promulgate rules whereby magis-
trates may be assigned duties “as are not inconsistent with the Constitution
and laws of the United States.” 28 U.S.C. § 636(b) (1970). The statute said
that “[t]he additional duties authorized by rule may include, but are not
restricted to . . . assistance to a district judge in the conduct of pretrial or
discovery proceedings in civil or criminal actions.” Id. The then-extant
statute made no mention of the procedure by which a district court is to
review a magistrate’s handling of a pretrial matter.
   6
     The defendant also raised a claim that § 636(b)(1) violated Article III,
but the Court rejected that claim and it is not at issue here.
                   UNITED STATES v. THOMS                      7707
is entitled to a de novo hearing on statutory grounds. We
therefore discuss only Raddatz’s constitutional holding.

   The Court began with the proposition that “[t]he guarantees
of due process call for a hearing appropriate to the nature of
the case.” Id. at 677 (internal quotation marks omitted). The
Court thus undertook a due process balancing inquiry before
concluding that “the due process rights claimed here are ade-
quately protected by § 636(b)(1).” Id. at 680. The Court then
added an important footnote at the conclusion of the due pro-
cess section. The footnote reads, in full:

        Neither the statute nor its legislative history
    reveals any specific consideration of the situation
    where a district judge after reviewing the record in
    the process of making a de novo “determination” has
    doubts concerning the credibility findings of the
    magistrate. The issue is not before us, but we assume
    it is unlikely that a district judge would reject a mag-
    istrate’s proposed findings on credibility when those
    findings are dispositive and substitute the judge’s
    own appraisal; to do so without seeing and hearing
    the witness or witnesses whose credibility is in ques-
    tion could well give rise to serious questions which
    we do not reach.

Id. at 681 n.7. Unfortunately, the Court did not specify the
nature of these “serious questions,” and it has not since Rad-
datz been presented with a case implicating them.

   The final case in the trilogy is United States v. Ridgway.
Ridgway had relevant facts similar to Bergera. The defendant
was indicted on drug charges, and he filed a motion to sup-
press. 300 F.3d at 1154-55. The magistrate heard testimony,
disbelieved the Drug Enforcement Administration (“DEA”)
agent, and recommended granting the motion. Id. at 1155.
Without conducting a de novo hearing, the district court
rejected the adverse credibility finding, because the district
7708               UNITED STATES v. THOMS
court thought that inconsistencies in the DEA agent’s testi-
mony were in fact “explained fully” during the agent’s cross-
examination. Id. The defendant was convicted following a
bench trial. Id. On appeal, this court vacated the order deny-
ing the motion to suppress and remanded because “a district
court errs when it does not conduct a de novo evidentiary
hearing if it rejects the credibility finding of a magistrate
judge who recommends the granting of a motion to suppress.”
Id. at 1157.

   [3] Ridgway’s reasoning is grounded in concepts of due
process. The Ridgway court began by noting that “[w]e
review de novo the question whether a defendant’s due pro-
cess rights were violated.” Id. at 1155. Ridgway then explic-
itly gives Bergera a narrow reframing in light of Raddatz. The
Ridgway court said:

    Although we held in Bergera that a district court is
    required to conduct a de novo evidentiary hearing
    before rejecting the factual determinations of a mag-
    istrate judge on a motion to suppress, we did not
    frame this issue in terms of a due process violation.
    In a case decided after we issued Bergera, however,
    the Supreme Court [in Raddatz] addressed a related
    issue and did frame its holding in terms of a defen-
    dant’s right to due process.

Id. at 1156.

   Ridgway’s holding is expressly limited to cases where a
defendant’s due process rights would be violated by the fail-
ure to hold a de novo evidentiary hearing. Moreover, Ridgway
says that Bergera must be read in light of the Supreme
Court’s Raddatz reframing of this issue in terms of due pro-
cess. Thus, the precedent we are required to follow is limited
to the proposition that a defendant has a right to a de novo
hearing when the district court rejects the magistrate’s credi-
bility findings that were favorable to the defendant. If the
                     UNITED STATES v. THOMS                   7709
right to an evidentiary hearing prior to rejection of the magis-
trate’s credibility findings is based solely on the Due Process
Clause, the principle is not symmetrical: the government has
no right to a de novo evidentiary hearing in all circumstances
where a magistrate’s credibility determination is reversed, for
the government concedes it has no due process rights. See
supra p. 7704 and note 4. Further, in 2007, this court reaf-
firmed the narrower, asymmetrical view of Ridgway and Ber-
gera when it said that “we reaffirmed in Ridgway that a
district court errs when it does not conduct a de novo eviden-
tiary hearing if it rejects the credibility finding of a magistrate
judge who recommends granting a motion to suppress.”
United States v. Hernandez-Acuna, 498 F.3d 942, 944 (9th
Cir. 2007) (emphasis added) (citation omitted).

   More recently, in Johnson v. Finn, 665 F.3d 1063 (9th Cir.
2011), our court encountered a case where the district court,
without holding a de novo hearing, reversed a magistrate’s
determination that a prosecutor had purposefully discrimi-
nated on the basis of race in exercising a peremptory strike of
a juror. Id. at 1065-66. We reversed. In so doing, we extended
the Ridgway rule to the Batson context, so that a defendant’s
due process rights are violated when a district court “de-
clin[es] the opportunity to observe the trial prosecutor’s
demeanor before rejecting the magistrate judge’s adverse
credibility finding.” Id. at 1066. The court in Johnson noted
the importance of the general interest in accurate factfinding,
stating that a district judge who rejects a credibility determi-
nation without holding a de novo hearing is “hampered by the
deficiencies of a cold record.” Id. at 1073. The court then
reaffirmed Ridgway’s understanding of Raddatz by saying
that “the Raddatz footnote applies generally to determinations
affecting the rights of a criminal defendant and involving a
credibility finding.” Id. at 1074 (emphasis added).

  [4] From these repeated invocations of the Due Process
Clause, we can discern that the absolute right to have a de
novo hearing in all circumstances where a district court
7710                UNITED STATES v. THOMS
reverses a magistrate’s credibility findings belongs only to
defendants or others who may assert due process rights. Thus,
we decline to adopt the government’s proposed broad rule and
extend that line of precedent to all such determinations
adverse to the government.

                               B.

   [5] But that does not end the matter. Our court has supervi-
sory authority “to mandate procedures deemed desirable from
the viewpoint of sound judicial practice although in nowise
commanded by statute or by the Constitution.” Thomas, 474
U.S. at 146-47 (internal quotation marks omitted). The long-
standing and repeated invocations in caselaw of the need of
district courts to hear live testimony so as to further the accu-
racy and integrity of the factfinding process are not mere plat-
itudes. Rather, live testimony is the bedrock of the search for
truth in our judicial system. After all, “[w]here an unresolved
factual dispute exists, demeanor evidence is a significant fac-
tor in adjudging credibility.” Townsend v. Sain, 372 U.S. 293,
322 (1963), overruled on other grounds by Keeney v.
Tamayo-Reyes, 504 U.S. 1, 5-6 (1992); see also Anderson v.
City of Bessemer City, N.C., 470 U.S. 564, 575 (1985)
(“[O]nly the trial judge can be aware of the variations in
demeanor and tone of voice that bear so heavily on the listen-
er’s understanding of and belief in what is said.”).

   [6] To further the integrity and accuracy of our judicial
process and to facilitate the search for truth, we therefore
adopt a narrower rule than the one that applies where due pro-
cess protections formally attach. We hold that a district court
abuses its discretion when it reverses a magistrate judge’s
credibility determinations, made after receiving live testimony
and favorable to the government, without viewing key demea-
nor evidence, with one exception: where the district judge
finds that the magistrate judge’s credibility determinations
had no legally sufficient evidentiary basis, so that, were they
jury determinations, judgment as a matter of law would issue
                    UNITED STATES v. THOMS                     7711
for the defendant. So that district courts may apply this rule
practically, we turn to the rule’s application in the context of
this case. As applied here, we vacate and remand the district
court’s orders for reconsideration.

   [7] The district court noted that “in many cases, a district
court might need to conduct a second evidentiary hearing”
before departing from a magistrate judge’s credibility find-
ings. But the district court failed to hold one for the following
reasons:

       [T]his court has had access to a transcript of the
    original evidentiary hearing and has explained at
    length [in the previously quoted order] how the evi-
    dence presented renders it highly improbable
    (indeed, it seems to this court in light of all the evi-
    dence, virtually impossible) that Investigator Young
    could smell the marijuana grow under the circum-
    stances that existed at the time. That conclusion
    would not change simply because this court heard
    the evidence all over again. The issue here does not
    turn on the demeanor of the witnesses, but rather on
    the implausibility of the officer’s conclusion that he
    smelled the marijuana grow inside a sealed building
    at least 450 feet away, which was screened by forest
    vegetation and a hill with a house on it. These con-
    siderations, which are paramount in rendering
    Young’s conclusion unbelievable, are either derived
    directly from or are entirely consistent with Investi-
    gator Young’s own testimony. It would serve no pur-
    pose but delay to conduct a second hearing to hear
    the testimony all over again.

D. Ct. Order on Reconsideration 5 (emphasis removed) (foot-
note omitted). These considerations are not enough to over-
come the strong presumption in favor of achieving integrity
and accuracy through hearing some live testimony anew
which we today adopt. The standard we import from Federal
7712                UNITED STATES v. THOMS
Rule of Civil Procedure 50 for judgment as a matter of law
in favor of Thoms was not met here. The evidence and testi-
mony in favor of the Thomses was not so overwhelming that
the district court could have found, as a matter of law, that no
reasonable factfinder could have credited Investigator
Young’s testimony.

   [8] In addition, the district court’s reasoning is speculative.
The district court stated that its “conclusion would not change
simply because this court heard the evidence all over again.”
But the district judge merely said that Young’s account was
“implausible” based on the cold record. Perhaps seeing Inves-
tigator Young’s demeanor as he testified to what he smelled
would have changed the outcome. The strong presumption in
our system is that demeanor evidence has important value. If
so, then the district judge’s certitude is misplaced. Surely,
there was some possibility the outcome would have been dif-
ferent had he heard live testimony. As one example, Investi-
gator Young could have been testifying truthfully without
undermining any of the considerations important to the dis-
trict court’s prior conclusion if the odor filtration system was
not working properly on the night Young said he smelled
marijuana. That it was working properly depended in part on
the evidence of the defendants, whose demeanor was not
observed by the district court. Or there might be other circum-
stances bolstering Young’s credibility that were not ruled out.

   Moreover, the district court’s reasoning discounts the gov-
ernment’s interest in the “accuracy and integrity” of the fact-
finding process which, after all, is the foundation of the due
process right given defendants. Given the stated importance
of demeanor evidence in our system, the strong presumption
is that the government is entitled to proffer it for its most
important witnesses before a district judge reverses a magis-
trate’s credibility finding in favor of the government. More-
over, other stakeholders—like Investigator Young and other
similar law enforcement officials—also share this interest in
the integrity of the proceedings. In this case, just as in most
                    UNITED STATES v. THOMS                 7713
cases where a district court grants a motion to suppress when
it rejects a magistrate’s credibility determination, the real-
world consequence of the district court’s decision is that the
police officer was lying or recklessly disregarding the truth in
his warrant affidavit. There is a strong possibility that such a
finding could have serious professional, or even legal, conse-
quences for Young. Yet the district judge discounted Investi-
gator Young’s interest in presenting his demeanor to the
district court. Put another way, before a district court calls a
police officer a liar, there is a strong presumption that the
judge should look him in the eye first.

   We recognize that not everyone agrees that demeanor evi-
dence and live testimony are as important to the integrity and
accuracy of the judicial process as we think it is. The district
court stated on the record that live testimony would be useless
in this case. Others have gone further and argued that the
biases created by hearing live testimony can actually detract
from factfinding accuracy, and that these biases may be espe-
cially acute in the context of suppression motions. They note
that police officers testify frequently, are professionally
trained to remain calm in difficult circumstances, and come
with a professional reputation of trustworthiness. Defendants
have none of those advantages, and the “very thing the defen-
dant seeks to suppress—evidence of criminal behavior—
suggests that he is less than an honest, upright citizen.” Wil-
liam J. Stuntz, Warrants and Fourth Amendment Remedies,
77 Va. L. Rev. 881, 914 (1991). Some think it likely that this
“credibility gap” can be lessened where a judge looks at a
cold record, since a cold record may permit the judge to focus
more on the substance of the testimony and less on witness
demeanor and appearance, which, at least in some circum-
stances, could be as misleading as they are helpful. “Perhaps,”
states a leading federal procedure treatise, “the entire Ameri-
can reliance on demeanor is misplaced.” Cf. 12 Charles Alan
Wright et al., Federal Practice & Procedure Civil § 3070.2
(2d ed.); see also id. at n.20 (“There is a considerable body
of psychological research indicating that in many contexts
7714                UNITED STATES v. THOMS
observing people tell stories does not enhance the ability to
determine whether the story is truthful, and may even corrupt
the ability to make accurate decisions about truthfulness.”).

   We disagree, and do not think we overvalue the importance
of live testimony. For one thing, the Supreme Court and our
court have repeatedly cited the value of live testimony with
respect. Perhaps more importantly, trial judges and juries in
our circuit and all over the country rely on the demeanor evi-
dence given by live testimony everyday, and they find it quite
valuable in making accurate decisions. Such testimony is in
fact indispensable, and the value of live, in-court testimony is
enshrined in the Sixth Amendment’s Confrontation Clause.
The value of live testimony is a large part of why our court
reviews district courts’ factual findings for clear error. Fur-
ther, the value of live testimony also contributes to the need
for trial and disregard of summary judgment when there is a
genuine factual dispute on a relevant issue. Here, for instance,
we are in the same position as the district court with respect
to assessing the credibility of the witnesses who testified
before the magistrate. But only the district court has the
option of adding to that record through live testimony. That
is a great advantage, which district courts should take in most
cases before reversing credibility determinations.

   We do wish to highlight two limitations on the scope of our
rule. First, as we have stated, the rule we adopt today is not
completely equivalent to the absolute right to de novo hear-
ings possessed by defendants. If the magistrate’s determina-
tion was so lacking in support that judgment as a matter of
law for the party who lost before the magistrate is appropriate,
a de novo hearing may not be in order. Having limited excep-
tions to the de novo hearing requirement where the govern-
ment’s interests are at stake puts us in line with the other
circuits to have considered this issue. Both the Second and
Eleventh Circuits have stated de novo hearings are required in
most, but not all, circumstances where a magistrate judge’s
credibility findings are reversed to the detriment of the gov-
                    UNITED STATES v. THOMS                   7715
ernment. See United States v. Cofield, 272 F.3d 1303, 1306
(11th Cir. 2001) (per curiam); Carrion v. Smith, 549 F.3d 583,
588 (2d Cir. 2008). The Thomses candidly admit that those
cases are on point, but they urge us to depart from the rule in
our sister circuits. We decline the invitation to create a circuit
split.

   Second, the de novo hearing before the district judge need
not be a rerun of the entire hearing that occurred before the
magistrate. Here, ten witnesses testified before the magistrate
over the course of two days, including an expert witness who
is a professor at the University of Pennsylvania, in Philadel-
phia. Where the inefficiencies of hearing live testimony from
a witness greatly outweigh the value of seeing demeanor evi-
dence, a district court can hold a more limited hearing than
that conducted by the magistrate. But here, as in many cases,
the key witnesses, Investigator Young and the defendants
likely live or work relatively near the courthouse. Further,
conducting a more limited hearing relieves the district court
of the heavy burden of entirely redoing the original hearing.
We leave it to the district court on remand to determine whose
live testimony it should hear to balance efficiency with the
integrity and accuracy interests we have described.

                              ***

   [9] In the business of judging, there is nothing more impor-
tant than getting the facts right. In many cases, factual deter-
minations are made after hearing live testimony regarding two
competing versions of critical events. To further the accuracy
and integrity of these determinations, we hold that a district
court abuses its discretion when it reverses a magistrate
judge’s credibility determinations, made after receiving live
testimony and favorable to the government, without viewing
key demeanor evidence, with one exception: where the dis-
trict judge finds that the magistrate judge’s credibility deter-
minations had no legally sufficient evidentiary basis, so that,
were they jury determinations, judgment as a matter of law
7716                 UNITED STATES v. THOMS
would issue for the defendant. As applied to this case, we
VACATE the orders on suppression and reconsideration and
REMAND for further consideration. That consideration on
remand, we presume, will include a de novo hearing before
the district judge, but we leave it to the district court to deter-
mine the scope of that hearing.

  VACATED and REMANDED.
