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       United States Court of Appeals
                  FOR THE DISTRICT OF COLUMBIA CIRCUIT




Argued October 4, 2004                    Decided November 5, 2004


                               No. 04-3026

                     UNITED STATES OF AMERICA,
                            APPELLANT

                                     v.

                          EDWARD N. HOLMES,
                              APPELLEE



          Appeal from the United States District Court
                  for the District of Columbia
                       (No. 03cr00508–01)



  John P. Gidez, Assistant U.S. Attorney, argued the cause
for appellant. With him on the briefs were Kenneth L.
Wainstein, U.S. Attorney, and John R. Fisher and Elizabeth
Trosman, Assistant U.S. Attorneys. Mary M. Petras, Assis-
tant U.S. Attorney, entered an appearance.

 Bills of costs must be filed within 14 days after entry of judgment.
The court looks with disfavor upon motions to file bills of costs out
of time.
                               2

  Lisa B. Wright, Assistant Federal Public Defender, argued
the cause for appellee. With her on the brief was A.J.
Kramer, Federal Public Defender.
  Before: ROGERS, TATEL, and GARLAND, Circuit Judges.
  Opinion for the Court filed by Circuit Judge TATEL.
  TATEL, Circuit Judge: The government appeals the district
court’s suppression of evidence the police discovered during a
search that, according to the district court, ran afoul of the
federal knock and announce statute. The district court,
however, failed to make a finding on a critical issue, i.e.,
whether the police announced ‘‘warrant’’ before entering the
premises, leaving us unable to perform our appellate function.
Accordingly, we vacate the district court’s order and remand
for further proceedings consistent with this opinion.

                                I.
   The knock and announce statute, 18 U.S.C. § 3109, pro-
vides that an ‘‘officer may break open any outer or inner door
or window of a house TTT to execute a search warrant, if,
after notice of his authority and purpose, he is refused
admittanceTTTT’’ ‘‘Codifying a tradition embedded in Anglo–
American law,’’ section 3109 declares the ‘‘reverence of the
law for the individual’s right of privacy in his house.’’ Miller
v. United States, 357 U.S. 301, 313 (1958). The principles
underlying the statute also form part of the Fourth Amend-
ment’s reasonableness inquiry, as the reasonableness of a
search of a dwelling may vary depending on whether the
police announced their presence and authority. Wilson v.
Arkansas, 514 U.S. 927, 930, 936 (1995).
   In this case, D.C. Metropolitan Police Officer Anthony
Guice, based on his affidavit that a ‘‘special employee’’ had
purchased drugs from ‘‘Eddie’’ at 800 Southern Avenue, S.E.,
Apartment 1214, obtained a search warrant for the premises.
To execute the warrant, Guice and several other officers
waited in a stairwell one floor below the apartment until
undercover officers stationed in the twelfth floor hallway
signaled that the ‘‘target’’ had just left Apartment 1214 and
was standing in the hallway at the apartment’s front door.
                               3

Led by Officer Andre Martin, the officers, wearing police
jackets and vests and with badges hanging around their
necks, rushed up the stairs to the apartment door, where they
found appellee Edward Holmes holding a set of keys.
   According to Martin, he twice said to Holmes, ‘‘[P]olice,
search warrant,’’ but—significantly for this appeal—the dis-
trict court never expressly made this finding. Taking the
keys from Holmes’s hand, Martin unlocked the door and
together with several other officers entered and seized a rifle,
several rounds of ammunition, and a bag of heroin. No one
was inside the apartment. The officers arrested Holmes, and
a grand jury later indicted him on one count of unlawful
possession of a firearm and ammunition by a convicted felon,
see 18 U.S.C. § 922(g)(1), one count of unlawful possession of
ammunition by a convicted felon, see id., and one count of
heroin possession, see 21 U.S.C. § 844(a).
   Before trial, Holmes moved to suppress the evidence seized
in the apartment, arguing that the police had violated section
3109. At the evidentiary hearing, the government called
Officer Guice, who testified that he reached the apartment
door ‘‘two to three seconds’’ after the first wave of officers,
and that he heard no exchanges between the officers and
Holmes. Asked whether the officers had knocked, Guice
answered no, explaining, ‘‘Since we had the keys, I didn’t feel
we needed to knock on the door.’’ Defense counsel argued
that this testimony demonstrated a violation of section 3109
because the officers ‘‘did not knock, did not announce, did not
say warrant, did not say anything to Mr. Holmes before
opening the door with the keys.’’
   The day after Guice testified, the prosecutor received per-
mission to reopen the hearing to call Officer Martin. Martin
testified that as he approached the door carrying a battering
ram, he said to Holmes, ‘‘Police, search warrant,’’ loudly
enough that anyone in the hallway would have heard. Ac-
cording to Martin, Holmes asked what was going on, at which
point Martin took the keys from Holmes’s hand and said,
‘‘This is a search warrant.’’ Martin also testified that he had
an exchange with Holmes during which Martin asked Holmes
                               4

which key opened the door, but the district court struck this
conversation as violating Federal Rule of Criminal Procedure
16, which requires the prosecution to turn over to defense
counsel evidence of any statements by the defendant.
   The government argued that if, during the execution of a
warrant, the defendant (1) has notice of the officers’ authority
and purpose and (2) is standing outside the door of his
dwelling, a formal knock and announce would be superfluous.
Relying on a Fourth Circuit decision, the government urged
the district court to find the officers’ actions reasonable under
the circumstances. See United States v. Dunnock, 295 F.3d
431, 435 (4th Cir.) (holding that knock and announce would
have been futile when defendant received ‘‘functional equiva-
lent of notice of authority and purpose’’ after police arrested
and questioned him about whether he had a key to the door
and whether anyone was inside), cert. denied, 537 U.S. 1037
(2002).
   In its findings of fact, the district court restated Martin’s
testimony, but made no finding as to whether Martin actually
announced ‘‘warrant’’ before taking Holmes’s keys and un-
locking the door. The court noted only that ‘‘there was a
conversation of some kind between Officer Martin and the
defendant,’’ presumably alluding to the discussion about
which key opened the door and possibly to Holmes’s asking
what was going on. Tr. 2/20/04 at 69. The district court also
found that the officers ‘‘knew nothing about whether there
was anyone else in the apartment, who the apartment was
rented to, who actually lived in the apartment, and did not
know for sure that the gentleman they stopped outside the
apartment, namely Mr. Holmes, was the ‘Eddie’ referred to in
the search warrant.’’ Tr. 2/20/04 at 76. Concluding that the
police had failed to comply with section 3109, and rejecting
the government’s functional equivalence argument, the dis-
trict court granted the motion to suppress the gun, the
ammunition, and the drugs.

                            II.
 Reiterating its position in the district court, the govern-
ment argues that the officers fulfilled the purposes of the
                                5

knock and announce statute despite their undisputed failure
to formally knock—the traditional means of providing notice
of police authority before entering a home—or to give Holmes
an opportunity to consent to or refuse their entry. Specifical-
ly, the government asserts that Martin, by twice identifying
himself and informing Holmes of the warrant, provided the
functional equivalent of notice of authority and purpose,
rendering irrelevant from Holmes’s perspective not only the
officers’ failure to knock, but also their ignorance as to
whether anyone was inside the apartment. Technical compli-
ance with section 3109, the government argues, is unneces-
sary when the search implicates none of the three core values
protected by the statute: ‘‘(1) reducing the potential for a
violent confrontation between the police and an occupant
startled by an unannounced intrusion; (2) preventing need-
less destruction of private property; and (3) showing respect
for the individual’s privacy interest in his home.’’ United
States v. Kemp, 12 F.3d 1140, 1142 (D.C. Cir. 1994). Accord-
ing to the government, violence in this case was unlikely
because Martin announced they were police officers with a
warrant, and no one was inside the apartment; no destruction
of private property occurred because the officers used
Holmes’s key to gain entry; and Holmes had only a minimal
privacy interest in the apartment because he was not in the
apartment and knew from Martin’s statement that a warrant-
authorized search was imminent.
   Significantly for our purposes, the government never ar-
gues that functional compliance with section 3109 could have
been achieved had Martin failed to provide notice by saying
‘‘warrant.’’ In other words, as the government explained at
oral argument, its theory that no section 3109 violation oc-
curred assumes that Martin in fact said ‘‘warrant.’’ The
district court’s failure to make a finding on this critical issue,
the government insists, presents no problem: since the court
never discredited Martin’s testimony, we should assume it
believed that Martin actually said ‘‘warrant.’’ For several
reasons, we cannot make such an assumption.
  To begin with, the district court’s findings are quite com-
prehensive, leaving us hesitant to assume that the court made
                                6

a finding it never mentioned. Reviewing those findings,
moreover, we cannot tell precisely what the district court
thought about Martin’s testimony. The court stated, ‘‘Ulti-
mately [Martin] took the keys from the defendant. There
was a conversation of some kind between Officer Martin and
the defendant. However, TTT the Court suppressed those
statements TTT because there had been a violation of rule 16.’’
Tr. 2/20/04 at 69. The district court also stated that Martin
testified
    he did not knock because he had the keys, TTT he never
    asked the defendant for permission to enter the apart-
    ment, and that was because the officer knew that there
    was a search warrant. Officer Martin also testified that
    he never asked whether anyone was inside the apart-
    ment, and that he had absolutely TTT no knowledge of
    whether anyone else was in the apartment.
Id. From these passages, we have no idea whether the
district court believed Martin announced ‘‘warrant,’’ but failed
to mention it, or whether the court discredited that state-
ment—either because it conflicted with Guice’s testimony that
he never heard Martin say anything at all, or because the
district court simply found Martin not credible on that issue.
Moreover, when describing Martin’s testimony that he was
the first to see Holmes standing in front of his apartment, the
district court stated that ‘‘the Court does credit Officer
Martin’s testimony on this.’’ Id. at 68 (emphasis added).
But the court neither explained what it thought about the
other aspects of Martin’s testimony discussed in its findings
nor even mentioned the warrant statement.
   The district court’s conclusions likewise reveal little about
whether the court credited Martin’s warrant testimony. ‘‘[I]t
is undisputed,’’ the district court said, ‘‘that the police did not
knock and announce, and certainly did not follow the require-
ments of the Federal statute.’’ Id. at 75 (emphasis added).
As Holmes points out, this could be read to suggest that the
court discredited Martin, for why else would it have found
that the police failed to ‘‘knock and announce’’? On the other
hand, as the government suggested at oral argument, perhaps
                               7

the district court used the phrase ‘‘knock and announce’’ to
indicate the officers would have violated the statute unless
they knocked and announced. Viewed this way, the district
court’s statement could mean that the court credited Martin’s
announcement of ‘‘police, search warrant,’’ but found the
absence of a formal knock to have violated section 3109.
Although the government’s interpretation is plausible, we
think it unwise to resolve an issue so critical to Holmes’s
claim on the basis of an assumption about what the district
court may have meant by the phrase ‘‘knock and announce.’’
   The government offers a second reason for assuming that
the district court credited Martin’s testimony: according to
the government, Martin’s testimony does not actually conflict
with Guice’s. Emphasizing Guice’s testimony that ‘‘Martin
and [another officer] got to [Holmes] prior to me getting to
him, and if they asked him anything, it was not to my
knowledge,’’ the government theorizes that Martin could have
said ‘‘warrant’’ to Holmes before Guice’s arrival. This theory
finds support in the district court’s statement that ‘‘[t]here
was a conversation of some kind between Officer Martin and
the defendant.’’ On the other hand, other testimony in the
record could be viewed as contradicting the government’s
theory. Martin testified that the other officers arrived at the
apartment door essentially at the same time and not more
than a second after he did. He also said he had announced
warrant loudly enough that the ‘‘other officers should have
heard.’’
   For his part, Holmes urges us to construe the record in the
light most favorable to upholding the district court’s ruling—
that is, to assume that the district court discredited Martin
and believed that the officers neither knocked nor announced.
Although this circuit has stated that ‘‘we must uphold the
ruling of the trial court if there is any reasonable view of the
evidence that will support it,’’ Scarbeck v. United States, 317
F.2d 546, 562 (D.C. Cir. 1962), we held in United States v.
Williams, 951 F.2d 1287, 1289 (D.C. Cir. 1991), that we will
not do so where we ‘‘do not know which facts the district
court considered ‘essential’ to its ruling,’’ see also United
States v. Jordan, 951 F.2d 1278, 1283 (D.C. Cir. 1991) (re-
                               8

manding appeal from a suppression motion denial for a
finding on a ‘‘key factor’’ for determining whether a seizure
occurred). We think this is such a case. Because we cannot
tell whether the district court believed that Martin said
‘‘warrant,’’ we find ourselves in the unusual situation of being
unable to deduce what, if any, role this crucial testimony
played in the district court’s disposition of this case. See
United States v. Johnson, 212 F.3d 1313, 1316 (D.C. Cir.
2000) (noting necessity of remand where there is ‘‘genuine
uncertainty about what the district court did’’). As the
government states in its reply brief, in such circumstances a
remand to resolve the ambiguity is warranted. See United
States v. Goree, 365 F.3d 1086, 1094-95 (D.C. Cir. 2004).

                              III.
  In sum, the district court’s failure to resolve the key
question of Martin’s credibility makes it impossible for us to
perform our appellate function. ‘‘The purpose of an appeal is
to review the judgment of the district court, a function we
cannot properly perform when we are left to guess at what it
is we are reviewing.’’ Williams, 951 F.2d at 1290. We
therefore vacate the district court’s order and remand for
further proceedings consistent with this opinion.
                                                    So ordered.
