                       PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,
               v.
                                           No. 08-4647
ISRAEL RAMOS-CRUZ, a/k/a Taylor,
a/k/a Tailor, a/k/a Sastre,
               Defendant-Appellant.
                                      
       Appeal from the United States District Court
        for the District of Maryland, at Greenbelt.
       Deborah K. Chasanow, Chief District Judge.
                 (8:05-cr-00393-DKC-1)

                 Argued: October 28, 2011

                Decided: January 18, 2012

       Before NIEMEYER, DUNCAN, and FLOYD,
                   Circuit Judges.



Affirmed by published opinion. Judge Duncan wrote the opin-
ion, in which Judge Niemeyer joined. Judge Floyd wrote a
separate opinion concurring in part and concurring in the
judgment.
2               UNITED STATES v. RAMOS-CRUZ
                         COUNSEL

ARGUED: Sapna Mirchandani, OFFICE OF THE FED-
ERAL PUBLIC DEFENDER, Greenbelt, Maryland, for
Appellant. John Alexander Romano, UNITED STATES
DEPARTMENT OF JUSTICE, Washington, D.C., for Appel-
lee. ON BRIEF: James Wyda, Federal Public Defender, Bal-
timore, Maryland, for Appellant. Lanny A. Breuer, Assistant
Attorney General, Greg D. Andres, Acting Deputy Assistant
Attorney General, James M. Trusty, Deputy Chief, Gang
Unit, UNITED STATES DEPARTMENT OF JUSTICE,
Washington, D.C.; Rod J. Rosenstein, United States Attorney,
Baltimore, Maryland, Chan Park, Robert K. Hur, Assistant
United States Attorneys, OFFICE OF THE UNITED
STATES ATTORNEY, Greenbelt, Maryland, for Appellee.


                         OPINION

DUNCAN, Circuit Judge:

   A jury convicted appellant Israel Ramos-Cruz on nine
criminal counts related to his membership in the gang La
Mara Salvatrucha (also known as "MS-13"). Ramos-Cruz
appeals his convictions under 18 U.S.C. § 1512(a)(1)(C) for
aiding and abetting witness-tampering murder and under 18
U.S.C. § 922(g)(5)(A) for being an illegal alien in possession
of a firearm. He also challenges the district court’s decision
to permit two witnesses to testify against him without reveal-
ing their names or other identifying information and the dis-
trict court’s denial of his motion to suppress evidence
obtained during a search of his home. Although the district
court based its § 1512(a)(1)(C) jury instructions on our deci-
sion in United States v. Harris, 498 F.3d 278 (4th Cir. 2007),
which—while this appeal was pending—was abrogated by the
Supreme Court’s decision in Fowler v. United States, 131 S.
Ct. 2045 (2011), we conclude that the error in instructing the
                   UNITED STATES v. RAMOS-CRUZ                          3
jury was harmless. Finding no other error, we affirm the dis-
trict court’s judgment.

                                    I.

                                   A.

   Ramos-Cruz is a citizen of El Salvador who entered the
United States illegally in 1999. In 2001, he was initiated into
a subgroup or "clique" of the MS-13 gang1 known as the Sail-
ors Locotes Salvatruchos Westside (the "Sailors") that oper-
ates primarily in Prince George’s County, Maryland, just
outside of Washington, D.C. As part of his initiation, Ramos-
Cruz took the nickname "Taylor." He eventually rose to a
leadership position within the Sailors, acting as clique leader
or "first word" from approximately 2003 to 2005. Although
Ramos-Cruz’s convictions were based upon wide-ranging
criminal activity, we focus on the events relevant to the issues
before us on appeal. We lay out additional facts as necessary
in our analysis.

                                   1.

   On November 21, 2003, three members of the Sailors par-
ticipated in the murder of Eluith Madrigal. Randy Calderon,
a Sailor, brought Madrigal to the home of Juan Carlos
Moreira, one of the founders of the Sailors clique, claiming
that Madrigal was a member of a rival gang. Nelson Bernal,
another founding member of the Sailors, was also present.
Calderon and Madrigal began to fight, and the fight ended
  1
    MS-13 is an international gang formed by El Salvadorian immigrants
in Los Angeles in the 1980s. The gang has since expanded back into Cen-
tral America, gaining prevalence in El Salvador, Honduras, Guatemala,
and Mexico. MS-13 cliques now exist in cities throughout the United
States, including the metro Washington, D.C. area, Los Angeles, Seattle,
Phoenix, Houston, Boston, and New York. For additional information
about the organization and operation of MS-13, see United States v. Ayala,
601 F.3d 256, 261 (4th Cir. 2010).
4                UNITED STATES v. RAMOS-CRUZ
with Calderon and Bernal stabbing Madrigal to death.
Moreira was angry that the murder had taken place in his
home, and he ordered Calderon and Bernal to dispose of the
body.

   Following Madrigal’s murder, Moreira drove Calderon,
Bernal, and Moreira and Bernal’s girlfriends to the residence
of clique leader Ramos-Cruz. At trial, Bernal’s girlfriend Sari
Llenas testified that, during the car ride, Calderon seemed
upset and mentioned calling the police.

   Once the group arrived, Ramos-Cruz conferred with
Moreira in private. Ramos-Cruz then announced that Moreira,
Calderon, and another member of the Sailors nicknamed
"Curly" were going to paint graffiti to commemorate the mur-
der of Madrigal. Bernal testified to hearing Calderon say, "I
know you think I’m not going to be tough enough, but noth-
ing [sic] going to find out. I’m not going to tell nobody. I
know you all want to kill me, but it’s okay . . . . I’m going
to be tough." J.A. 874-75. Ramos-Cruz did not respond, and
Moreira told Calderon to shut up. Emilia Masaya, a member
of the Sailors also present at Ramos-Cruz’s home, testified to
seeing Ramos-Cruz give Moreira a gun before Moreira left
with Calderon.

   Calderon did not return to Ramos-Cruz’s residence that
night; Moreira and Curly reappeared alone. Masaya testified
to hearing Moreira tell Ramos-Cruz, "I got him." J.A. 1378.
Members of the Prince George’s County Police Department
found Calderon’s body the next morning—the morning of
November 22, 2003—near a bridge next to a can of spray
paint. Calderon had been shot in the head.

   Ramos-Cruz convened a meeting of the Sailors several
days later. During this gathering, he announced that Moreira
had killed Calderon because Calderon had violated a gang
rule and because he was considering talking to the police.
                 UNITED STATES v. RAMOS-CRUZ                 5
These events form the basis of Ramos-Cruz’s conviction
under § 1512(a)(1)(C).

                              2.

   In January 2004, the federal Bureau of Alcohol, Tobacco,
Firearms and Explosives ("ATF") began a collaboration with
the Prince George’s County Police Department known as the
Regional Anti-Gang Enforcement ("RAGE") Task Force. The
purpose of this collaboration was to address increased gang
violence in the greater Washington metropolitan area. MS-13
was a primary focus of the task force.

   On August 17, 2004, members of the RAGE task force exe-
cuted a search warrant for Ramos-Cruz’s residence. The war-
rant authorized officers to search the premises for evidence of
malicious destruction of property. During their search, offi-
cers seized a loaded .380 caliber semiautomatic handgun. The
DNA found on the gun matched Ramos-Cruz’s DNA. Offi-
cers also seized other evidence, including several machetes; a
fixed-blade knife; gloves marked with "MS-13," "Taylor,"
and "SLSW"; and a composition book containing MS-13 graf-
fiti designs. The firearm found during this search, combined
with Ramos-Cruz’s immigration status, discussed further
below, form the basis of his conviction under § 922(g)(5)(A).

                              B.

   On June 4, 2007, a federal grand jury returned a fourth
superseding indictment against Ramos-Cruz and fifteen others
for crimes arising out of their involvement in MS-13. Ramos-
Cruz was charged with conspiracy to participate in racketeer-
ing activity in violation of 18 U.S.C. § 1962(d), assault with
a dangerous weapon in aid of racketeering in violation of 18
U.S.C. § 1959(a)(3), conspiracy to commit murder in aid of
racketeering in violation of 18 U.S.C. § 1959(a)(5), murder in
aid of racketeering in violation of 18 U.S.C. § 1959(a)(1),
witness-tampering murder in violation of 18 U.S.C.
6                UNITED STATES v. RAMOS-CRUZ
§ 1512(a)(1)(C), two counts of use and carrying of a firearm
during a crime of violence in violation of 18 U.S.C. § 924(c),
murder resulting from the use and carrying of a firearm during
a crime of violence in violation of 18 U.S.C. § 924(j), and
being an illegal alien in possession of a firearm in violation
of 18 U.S.C. § 922(g)(5)(A).

                              1.

   Prior to trial, Ramos-Cruz moved to suppress the evidence
obtained during the August 17, 2004 search of his home. He
argued that the affidavit on which the search warrant was
based was insufficient to establish probable cause and that
officers violated the knock-and-announce rule when they
entered his residence. At a December 10, 2007, hearing before
the district court, Ramos-Cruz withdrew his knock-and-
announce argument, acknowledging that the Supreme Court’s
decision in Hudson v. Michigan, 547 U.S. 586 (2006), estab-
lished that the exclusionary rule does not apply to knock-and-
announce violations. The court then denied Ramos-Cruz’s
motion.

   Also prior to trial, the government moved for permission
for two El Salvadorian police officers to testify under pseud-
onyms and without revealing their dates and places of birth
and home and work addresses. The government based its
request on concern for the safety of the two officers and their
families were it made public that they had testified against
MS-13 members in a U.S. court. Ramos-Cruz objected,
emphasizing his need to investigate the witnesses’ back-
grounds independently. The government submitted in camera
affidavits from both prospective witnesses explaining the
threat against them; it also disclosed to Ramos-Cruz in
advance the substance of their proposed testimony. The dis-
trict court noted that it had previously permitted these two
witnesses to testify under the same precautionary measures in
earlier trials involving the same MS-13 conspiracy. See
United States v. Zelaya, 336 F. App’x 355, 357-58 (4th Cir.
                 UNITED STATES v. RAMOS-CRUZ                 7
2009) (unpublished) (affirming the district court’s decision).
It then conducted an ex parte hearing to determine whether
the circumstances that had persuaded it to allow these wit-
nesses to testify under pseudonyms in the past still existed.
The court concluded that the potential threat to the officers’
safety remained significant. The court also questioned the wit-
nesses and determined that the government had no disclosure
obligations under Giglio v. United States, 405 U.S. 150, 154-
55 (1972). Accordingly, the district court granted the govern-
ment’s motion.

                              2.

   Ramos-Cruz’s trial began on February 5, 2008. He was
tried with Santos Maximino Garcia, after the trials of the
other defendants charged in the fourth superseding indictment
were severed. Ramos-Cruz pleaded not guilty to all charges
against him. A six-week trial ensued.

   At trial, the government presented evidence regarding the
facts discussed above relevant to Ramos-Cruz’s convictions
under § 1512(a)(1)(C) and § 922(g)(5)(A). It also presented
additional evidence about Ramos-Cruz’s immigration status,
which is pertinent to Ramos-Cruz’s § 922(g)(5)(A) conviction
for being an illegal alien in possession of a firearm.

   At issue with respect to § 922(g)(5)(A) was whether
Ramos-Cruz had a pending application for temporary pro-
tected status ("TPS") pursuant to 8 U.S.C. § 1254a(b)(1) on
August 17, 2004, when officers found him in possession of a
firearm. Ramos-Cruz argued that if he had a pending applica-
tion, he was not in the United States illegally.

   TPS provides temporary benefits for citizens of foreign
states in which circumstances exist that would prevent nation-
als of the state from returning in safety, such as an ongoing
armed conflict or a natural disaster. El Salvador, Ramos-
Cruz’s native country, has been designated as such a state
8                   UNITED STATES v. RAMOS-CRUZ
since 2001. Aliens are prima facie eligible for TPS if they
have been continuously present in the United States since the
most recent designation of the relevant state—or a date desig-
nated by the attorney general—and if they have not, inter alia,
been convicted of a felony or two or more misdemeanors
committed in the United States. 8 U.S.C. § 1254a(c)(1)(A),
(c)(2)(B). An applicant who establishes a prima facie case of
eligibility for TPS is given two temporary benefits during the
pendency of his application: protection from removal and
authorization to seek employment. Id. at § 1254a(a)(4)(B).
These benefits remain in place until a final determination has
been made with respect to the alien’s eligibility for TPS. Id.
It is undisputed that after Ramos-Cruz entered the country
illegally in 1999, he applied for TPS in 2001.

  To address this issue, the government called former Immi-
gration and Customs Enforcement ("ICE") officer James
Colomb, who originally created Ramos-Cruz’s alien file.
Colomb testified that Ramos-Cruz initially appeared to have
made a prima facie case of eligibility and, on June 22, 2001,
was provided with employment authorization during the pen-
dency of his TPS application.2 His employment authorization
was extended on January 16, 2003, and again on November
13, 2003.

  Colomb testified, however, that ICE records further indi-
cated that Ramos-Cruz’s TPS application was denied on
March 19, 2004. He also stated that ICE appears to have sent
an intent-to-deny letter on March 31, 2004. Colomb
explained:

        We have to send a notice of intent to deny out first
        . . . saying . . . we’re going to deny unless this hap-
        pens. It’s very possible they did the denial first inad-
    2
    Colomb based his testimony on an ICE computer printout, introduced
at trial as the government’s exhibit "Record 8." J.A. 2106.
                 UNITED STATES v. RAMOS-CRUZ                   9
    vertently and then went ahead and sent the notice of
    intent to deny after the fact.

J.A. 2130. Upon further questioning, he confirmed that
Ramos-Cruz’s TPS application "would have been denied."
J.A. 2131. Colomb did not specify why. Colomb also stated
that Ramos-Cruz had never been granted TPS.

   Ramos-Cruz called his immigration attorney, Jaime
Aparisi, in an attempt to demonstrate that his application for
TPS was still pending in August 2004. After conducting voir
dire of Aparisi outside the presence of the jury, the district
court determined that he had no testimony to offer pertinent
to Ramos-Cruz’s immigration status at the relevant time and
declined to allow him to testify. Ramos-Cruz called no other
witnesses and introduced no exhibits relevant to this question.

                               3.

   At the close of evidence, Ramos-Cruz moved for a judg-
ment of acquittal on all counts. The district court denied the
motion, then proceeded to instruct the jury. In relevant part,
it explained that, the three elements the jury must find to con-
vict Ramos-Cruz of violating § 1512(a)(1)(C) were (1) that "a
person committed the premeditated murder of Randy Calde-
ron," (2) "that the person acted knowingly and with intent to
hinder, delay[,] or prevent the communication to a law
enforcement officer of the United States of information relat-
ing to the commission or possible commission of a federal
offense," and (3) "that the defendant aided and abetted that
person." J.A. 3877. It further explained that, for the jury to
find the second element,

    [t]he [g]overnment does not have to prove that the
    person specifically intended to interfere with a fed-
    eral investigation. All the statute requires is that the
    [g]overnment establish that at the time the person
    engaged in obstructionist conduct, he had the intent
10               UNITED STATES v. RAMOS-CRUZ
     to influence an investigation that eventually hap-
     pened to be federal and that the investigation
     involved the possible commission of a federal crime.

J.A. 3879. Ramos-Cruz objected to this instruction, stating
that it did not correctly explain the federal nexus required for
conviction under § 1512(a)(1)(C). He also objected to the jury
instructions regarding § 922(g)(5)(A), which stated that a per-
son with a pending TPS application is in the United States
illegally. The district court overruled both of his objections.

  The jury convicted Ramos-Cruz of all counts. The district
court sentenced him to life in prison, plus 35 years.

                              II.

   On appeal, Ramos-Cruz raises four arguments. First, he
contends that, in light of the Supreme Court’s decision in
Fowler, the district court improperly instructed the jury
regarding the requirements for conviction under
§ 1512(a)(1)(C). Second, he contests the district court’s denial
of his motion for judgment of acquittal on his conviction
under § 922(g)(5)(A). Third, he argues that the district court’s
decision to allow the two El Salvadorian witnesses to testify
without revealing their names or other identifying information
violated his rights under the Confrontation Clause. Finally, he
contends that the district court improperly denied his motion
to suppress the evidence obtained during the August 17, 2004
search of his residence. We address these arguments in turn.

                              A.

   We first consider the effect of Fowler on our
§ 1512(a)(1)(C) jurisprudence. Section 1512(a)(1)(C) pun-
ishes the murder or attempted murder of another person "with
intent to . . . prevent the communication by any person to a
law enforcement officer . . . of the United States of informa-
tion relating to the commission or possible commission of a
                 UNITED STATES v. RAMOS-CRUZ                11
[f]ederal offense." In Harris, we considered the issue of what
the government must show to allow a jury to make a suffi-
cient connection between the communication the defendant
acted to prevent and federal law enforcement officers. We
explained that "[s]o long as the information the defendant
seeks to suppress actually relates to the commission or possi-
ble commission of a federal offense, the federal nexus
requirement is established." Harris, 498 F.3d at 286. The dis-
trict court followed this guidance when instructing the jury
below.

   Ramos-Cruz contends that, following the intervening
Supreme Court decision in Fowler, our interpretation of
§ 1512(a)(1)(C) is no longer valid, and his conviction on this
count must be reversed. We agree that Fowler rendered the
jury instructions incorrect, but for the reasons discussed
below, we find the instructional error harmless.

   In Fowler, the Supreme Court considered the evidentiary
showing necessary to sustain a conviction under
§ 1512(a)(1)(C) in circumstances—analogous to those
here—in which a defendant killed his victim to prevent com-
munication with law enforcement in general, rather than with
federal law enforcement specifically. 131 S. Ct. at 2048.
Charles Fowler shot and killed a local police officer when the
officer discovered Fowler and several other men preparing to
rob a bank. He was convicted of violating § 1512(a)(1)(C).
On appeal, he argued that the government had not offered suf-
ficient evidence to show that Fowler had killed the officer to
prevent him from communicating with federal officers. The
Eleventh Circuit affirmed Fowler’s conviction, holding that
"the possible or potential communication to federal authori-
ties of a possible federal crime is sufficient for the purposes
of section 1512(a)(1)(C)." United States v. Fowler, 603 F.3d
883, 888 (11th Cir. 2010), overruled by Fowler v. United
States, 131 S. Ct. 2045 (2011).

   The Supreme Court rejected the Eleventh Circuit’s "possi-
ble or potential communication" test. Fowler, 131 S. Ct. at
12               UNITED STATES v. RAMOS-CRUZ
2051-52. The Court first confirmed that § 1512(a)(1)(C) does
apply to "a defendant who kills with intent to prevent commu-
nication with law enforcement officers generally," but only if
the government in such a case makes a showing about "the
likelihood of a hypothetical communication with a federal law
enforcement officer." Id. at 2050. The showing must demon-
strate more than a mere possibility that the victim would have
communicated with federal law enforcement officers, princi-
pally because much conduct punishable under state law also
violates federal law, and "where a federal crime is at issue,
communication with federal law enforcement officers is
almost always a possibility." Id. at 2051. Thus, the Supreme
Court reasoned, the Eleventh Circuit’s formulation would
"weaken or eliminate the independent force of" the language
"of the United States" included in the statute and impermiss-
ibly broaden it to cover much criminal conduct that is "purely
state in nature." Id. at 2051-52 (emphasis omitted).

   The Supreme Court went on to hold that the appropriate
standard for determining whether the government has demon-
strated the appropriate federal nexus is whether it has shown
"a reasonable likelihood that had, e.g., the victim communi-
cated with law enforcement officers, at least one relevant
communication would have been made to a federal law
enforcement officer." Id. at 2052. In making this showing,
"[t]he [g]overnment need not show that such a communica-
tion, had it occurred, would have been federal beyond a rea-
sonable doubt, nor that it is even more likely than not." Id. It
is required to show, however, "that the likelihood of commu-
nication to a federal officer was more than remote, outlandish,
or simply hypothetical." Id. The Supreme Court remanded to
the Eleventh Circuit to apply its newly articulated test. Id. at
2053.

   Because the test we articulated in Harris is analogous to
that overturned in Fowler, we recognize that Harris is no lon-
ger controlling. Further, because the district court here relied
on Harris in instructing the jury, its § 1512(a)(1)(C) instruc-
                     UNITED STATES v. RAMOS-CRUZ                           13
tions were erroneous as to the federal nexus element of the
offense.3 A misinstruction regarding an element is nonetheless
subject to harmless-error review. See Neder v. United States,
527 U.S. 1, 9-10 (1999); United States v. Brown, 202 F.3d
691, 699 (4th Cir. 2000).

   We find an error in instructing the jury harmless if it is
"clear beyond a reasonable doubt that a rational jury would
have found the defendant guilty absent the error." Neder, 527
U.S. at 18. In Brown, we considered whether the omission4 of
a jury instruction was harmless error in a situation analogous
to that here: the district court declined to give an instruction
not required under precedent that the Supreme Court later
superseded. Brown, 202 F.3d at 698-99. To determine
whether such an error was harmless under such circum-
stances, we mandated two inquiries. "First, where ‘a review-
ing court concludes beyond a reasonable doubt that the
omitted element was uncontested and supported by over-
whelming evidence, . . . then the erroneous instruction is
properly found to be harmless.’" Id. at 700 (quoting Neder,
527 U.S. at 17). Second, if the defendant contested the omit-
ted element, we ask "whether ‘the record contains evidence
that could rationally lead to a contrary finding with respect to
that omitted element.’" Id. at 701 (quoting Neder, 527 U.S. at
19). If not, then the error was harmless. Id. If so, however,
reversal is necessary. Id. at 703.
  3
     We review the denial of a request for a particular jury instruction for
abuse of discretion. United States v. Lighty, 616 F.3d 321, 366 (4th Cir.
2010). Here, Ramos-Cruz objected to the district court’s instructions on
the ground that they did not properly explain the federal nexus required
for conviction. Fowler rendered the district court’s instructions incorrect
with regard to that element of the offense, so the denial of Ramos-Cruz’s
request constituted an abuse of discretion.
   4
     Although the error in Brown involved an omitted jury instruction and
the error here is an erroneous instruction, we apply the same analysis. See
202 F.3d at 699 ("Although the error in Neder was based on a misinstruc-
tion, and the . . . error here is based on the omission of a required instruc-
tion, both errors effectively withdrew an element of the offense from the
jury’s consideration." (footnote omitted)).
14                  UNITED STATES v. RAMOS-CRUZ
  Here, we must first determine if the question of whether
Calderon was planning to communicate with federal law
enforcement officers was contested at trial. If so, to determine
whether the misinstruction was harmless error, we must
review the record with an eye to whether, based on the evi-
dence presented, a jury rationally could have found that there
was no reasonable likelihood that had Calderon "communi-
cated with law enforcement officers, at least one relevant
communication would have been made to a federal law
enforcement officer." Fowler, 131 S. Ct. at 2052.

   The government contends that the jury heard sufficient evi-
dence at trial to render the erroneous instruction harmless.5 It
first points to the fact that federal charges were filed in this
case related to the murder of Madrigal. It cites to testimony
about the formation of the RAGE task force—involving both
local and federal law enforcement—approximately one month
after Calderon’s murder. The jury also heard testimony that
RAGE was focusing on the activities of MS-13 and specifi-
cally "looking at homicides and assaults that were committed
by the gang members." J.A. 3583. Finally, the government
  5
    The government also contends that Ramos-Cruz waived his objection
to the jury instructions by not specifically raising the argument in his
opening brief, citing our prudential doctrine requiring that a claim be
raised at that point. See, e.g., Yousefi v. INS, 260 F.3d 318, 326 (4th Cir.
2001) (finding that appellant waived an argument not raised in his opening
brief). We decline to apply that doctrine here for two reasons. First,
Ramos-Cruz preserved his objection to the § 1512(a)(1)(C) conviction by
including it in his opening brief—albeit framed as a sufficiency of the evi-
dence challenge—even though, at the time, Harris controlled in this cir-
cuit. Second and more importantly, we ordered supplemental briefing in
this case following the Supreme Court’s decision in Fowler, and in his
supplemental brief, Ramos-Cruz outlined his objection to the jury instruc-
tions. Inclusion of this argument during supplemental briefing—which
was initiated by this court and at which point we often accept additional
arguments—fulfilled the important goal of putting the government on
notice as to the substance of Ramos-Cruz’s argument. As such, Ramos-
Cruz’s failure to explicitly challenge the jury instructions in his opening
brief does not preclude him from doing so now.
                 UNITED STATES v. RAMOS-CRUZ                15
notes that Detective Paula Hamill, the local police officer who
investigated Madrigal’s murder, testified to exchanging infor-
mation about her investigation with ATF and the U.S. Attor-
ney’s office. There is other record evidence that supports the
government’s position, as well. Specifically, former MS-13
member Noe Cruz reported that he had begun cooperating
with authorities in December 2003 and testified to speaking
with federal prosecutors while serving as an informant
between 2003 and 2005.

   At trial, Ramos-Cruz did not contest—either on direct or
cross-examination—the government’s evidence about the for-
mation of the RAGE task force, the focus of the RAGE task
force, or Detective Hamill’s cooperation with federal authori-
ties during the investigation of Madrigal’s murder. Ramos-
Cruz called into question the credibility of Cruz on cross-
examination; he never, however, specifically challenged his
statements about cooperating with federal officers. In light of
this uncontested evidence, we conclude that no rational juror
could have found that there was not a reasonable likelihood
that, had Calderon communicated with authorities, at least one
relevant communication would have been to a federal law
enforcement officer.

   We base this conclusion on the guidance in Fowler, which
emphasized that the government does not need to show "be-
yond a reasonable doubt (or even that it is more likely than
not) that the hypothetical communication would have been to
a federal officer." 131 S. Ct. at 2050. The government does,
however, need to show more than "a mere possibility that a
communication would have been with federal officials," id. at
2051, and that "the likelihood of communication to a federal
officer was more than remote, outlandish, or simply hypothet-
ical," id. at 2052. The government here presented enough evi-
dence that a rational jury would necessarily conclude it was
sufficiently likely that, had Calderon communicated with
police, at least one relevant communication would have been
made to federal law enforcement officers. In drawing this
16               UNITED STATES v. RAMOS-CRUZ
conclusion, we do not focus solely upon the fact that Madri-
gal’s murder was eventually prosecuted as a federal crime.
Instead, we follow the Third Circuit in holding that the federal
nexus element of § 1512(a)(1)(C) "may be inferred by the
jury from the fact that the offense was federal in nature, plus
additional appropriate evidence." United States v. Bell, 113
F.3d 1345, 1349 (3d Cir. 1997) (quoting United States v.
Stansfield, 101 F.3d 909, 918 (3d Cir. 1996)); accord United
States v. Rodriguez-Marrero, 390 F.3d 1, 13 (1st Cir. 2001)
(adopting the Bell standard); United States v. Diaz, 176 F.3d
52, 91 (2d Cir. 1999) (same); United States v. Causey, 185
F.3d 407, 422 (5th Cir. 1999) (same); United States v. Emery,
186 F.3d 921, 925 (8th Cir. 1999) (same). We consider vital
the additional evidence of the formation of the RAGE task
force shortly after Madrigal’s murder, RAGE’s focus on
investigating MS-13, Detective Hamill’s communication with
federal authorities regarding Madrigal’s murder, the testi-
mony of MS-13 informants explaining that they had spoken
with federal law enforcement officers, and Ramos-Cruz’s fail-
ure to contest any of this evidence. In light of this uncontro-
verted and overwhelming proof, we do not believe that "the
record contains evidence that could rationally lead to a con-
trary finding with respect to the omitted element." See Neder,
527 U.S. at 19. We therefore find that the error in instructing
the jury was harmless.

   Ramos-Cruz raises two additional arguments, asserting that
the fact that Madrigal’s murder was eventually prosecuted as
a state crime and that the RAGE task force did not exist at the
time of the murders both undermine a finding that the reason-
able likelihood standard was met. Ramos-Cruz did not bring
forth these arguments at trial and relies instead upon the gov-
ernment’s examination of its own witnesses as support for his
position.

  Fowler supports our rejection of these arguments. First, the
Supreme Court recognized that "when a defendant acts in
ways that violate state criminal law, some or all of those acts
                    UNITED STATES v. RAMOS-CRUZ                         17
will violate federal criminal law as well." Fowler, 131 S. Ct.
at 2051. It made this observation as a point against allowing
the mere fact that a crime could be federal to supply the fed-
eral nexus required by § 1512(a)(1)(C). See id. In doing so,
however, it certainly did not suggest that, when other evi-
dence demonstrated a reasonable likelihood of communica-
tion with a federal officer, the fact that the underlying crime
could have been prosecuted under both state and federal law
precluded prosecution under § 1512(a)(1)(C). See id.; accord
Rodriguez-Marrero, 390 F.3d at 13 (finding that a murder that
could have been prosecuted under state law but was included
as part of a federal indictment constituted a federal offense for
the purposes of § 1512(a)(1)(C)).

   Second, Fowler specifically noted that prosecution under
§ 1512(a)(1)(C) reaches killings that occur before the victim
has had any communication with law enforcement officers.
131 S. Ct. at 2049. This statement undermines Ramos-Cruz’s
argument that the federal investigation must be in effect at the
time of the murder. As such, we join our sister circuits in rec-
ognizing that the government need not prove that a federal
investigation was in progress at the time the defendant com-
mitted witness-tampering murder. See, e.g., United States v.
Romero, 54 F.3d 56, 62 (2d Cir. 1995) (holding that, to sus-
tain a conviction under § 1512(a)(1)(C), "[t]here need not be
an ongoing investigation or even any intent to investigate").6
Moreover, to require that federal and state officials had been
cooperating at the time of the murder would undermine the
deterrent purpose of the statute. See Fowler, 131 S. Ct. at
2049-50. When, as occurred here, federal law enforcement
authorities become involved in an investigation approximately
  6
   We recognize that proof of an ongoing federal investigation can pro-
vide the additional evidence required to sustain a conviction under
§ 1512(a)(1)(C). See, e.g., Rodriguez-Marrero, 390 F.3d at 13 (upholding
defendant’s conviction under § 1512(a)(1)(C) because, inter alia, federal
authorities had launched an investigation prior to the victim’s murder). We
merely hold that evidence of an ongoing federal investigation is not
required where, as is the case here, other appropriate evidence exists.
18                  UNITED STATES v. RAMOS-CRUZ
a month after the relevant murder, federal authorities are spe-
cifically focusing on the group in question, and local authori-
ties investigating the underlying crime are actively
cooperating with federal law enforcement officers, the reason-
able likelihood standard is met.

                                    B.

   Ramos-Cruz next challenges his conviction under
§ 922(g)(5)(A) for being an illegal alien in possession of a
firearm. Ramos-Cruz contends that because his TPS applica-
tion was pending at the time he was found in possession of a
firearm and, as such, he was not illegally in the country, the
district court improperly denied his motion for acquittal.7
Because we believe that the government presented more than
sufficient evidence to allow the jury to conclude that Ramos-
Cruz’s application for TPS had been denied at the relevant
time, we affirm.

   We review a district court’s denial of a motion for acquittal
de novo. United States v. Campbell, 977 F.2d 854, 856 (4th
Cir. 1992). In doing so, we "must decide whether, viewing the
evidence in the light most favorable to the government, any
rational trier of facts could have found the defendant guilty
beyond a reasonable doubt." Id. (internal quotation marks
omitted).

   Section 922(g)(5)(A) prohibits possession of firearms by
aliens who are "illegally or unlawfully in the United States."
The statute does not define these terms. The district court
instructed the jury that a person would be "illegally or unlaw-
  7
    Ramos-Cruz’s brief is not entirely clear regarding whether he is
appealing the denial of his motion for judgment of acquittal or the jury
instructions. Because he concludes the section of his brief discussing this
point by referencing the motion for judgment of acquittal and because the
government understood his argument to refer only to the motion for judg-
ment of acquittal—and therefore only had notice about this argument—we
address the district court’s holding regarding that motion.
                 UNITED STATES v. RAMOS-CRUZ                  19
fully" in the country for purposes of the statute even if he had
a pending TPS application at the relevant time. Ramos-Cruz
challenges this interpretation. He contends, as he did at trial,
that the district court should have instructed the jury that a
person with a pending TPS application is lawfully in the
United States. Neither party disputes, however, that a person
who entered the country illegally and had been denied TPS
status would be an illegal alien. For the reasons discussed
below, we believe the evidence presented at trial would have
easily allowed a rational jury to determine that Ramos-Cruz’s
application for TPS had been denied on August 17,
2004—when he was found in possession of a firearm. We
therefore decline to reach the statutory interpretation issue
Ramos-Cruz urges upon us.

   We base our conclusion on the evidence presented at trial.
Specifically, the government’s witness James Colomb testi-
fied several different times that Ramos-Cruz’s application for
TPS had been denied on March 19, 2004. Although Ramos-
Cruz attempted through cross-examination and the unsuccess-
ful attempt to call Aparisi as a witness to establish that
Ramos-Cruz’s application was still pending at the relevant
time, the jury never heard any testimony to that effect. In fact,
the final exchange between Ramos-Cruz’s attorney and
Colomb on cross-examination seems to have definitively
established that Ramos-Cruz’s application was no longer
pending:

    Q. Okay. So you are stating here today that there
    is not, in [Ramos-Cruz’s] A file, an application for
    temporary status that would have postdated March
    31, 2004. You’re certain of that.

    A.   To my knowledge, no.

J.A. 2133. In sum, the government presented ample evidence
to allow a rational jury to conclude that Ramos-Cruz did not
have a pending TPS application at the relevant time.
20                UNITED STATES v. RAMOS-CRUZ
   On appeal, Ramos-Cruz argues that ICE had not come to
a final decision regarding his TPS application at the relevant
time, which he asserts is demonstrated by the fact that Ramos-
Cruz allegedly had a valid employment authorization card in
August 2004. In support of this argument, he makes claims
that were not brought forth at trial and cites to documents
from his alien file that he did not introduce or refer to at trial.
To the extent Ramos-Cruz attempts to introduce new evidence
before us, we will not consider it for the first time on appeal.
Even if we did, the evidence to which he refers does not con-
tradict the evidence the government presented demonstrating
that Ramos-Cruz’s application was denied in March 2004. At
most, it shows that Ramos-Cruz was issued an extension to
his employment authorization in November 2003 that was not
set to expire until March 2005. The extension was issued
before the denial of his TPS application in March 2004, and
even assuming the employment authorization was technically
still valid in August 2004—which Ramos-Cruz presented no
evidence of—we are not persuaded that an expiration date for
a separate document set months prior to the denial of Ramos-
Cruz’s TPS application in any way indicates that the denial
was not final.

                                C.

   Ramos-Cruz also challenges the district court’s decision to
allow two government witnesses to testify under pseudonyms
and without revealing their names, home and work addresses,
or dates and places of birth. He contends that this ruling vio-
lated his Sixth Amendment right to confrontation, arguing
that without the withheld information, he was not able to con-
duct independent research about the witnesses’ veracity. "We
review for abuse of discretion a trial court’s limitations on a
defendant’s cross-examination of a prosecution witness."
United States v. Smith, 451 F.3d 209, 220 (4th Cir. 2006).

   In general, the Confrontation Clause guarantees a defendant
the right to question an adverse witness about identifying
                 UNITED STATES v. RAMOS-CRUZ                  21
information, including his full name and address. Smith v. Illi-
nois, 390 U.S. 129, 131 (1968) ("[T]he very starting point in
exposing falsehood and bringing out the truth through cross-
examination must necessarily be to ask the witness who he is
and where he lives." (footnote omitted)). We have recognized
that this right is not absolute, however, and that "a trial court
may limit cross-examination if the information sought could
endanger the witness." Chavis v. North Carolina, 637 F.2d
213, 226 (4th Cir. 1980). When the government seeks to with-
hold a witness’s true name, address, or place of employment,
it bears the burden of demonstrating that "the threat to the wit-
ness [is] actual and not a result of conjecture." United States
v. Palermo, 410 F.2d 468, 472 (7th Cir. 1969). If the govern-
ment makes a showing of an actual threat, the district court
still has discretion to review relevant information and deter-
mine whether disclosure of the witness’s identifying informa-
tion is necessary to allow effective cross-examination. Id.

   As the district court noted, we previously approved of its
decision to allow the identical El Salvadorian witnesses who
testified here to testify under the same circumstances in
another trial involving the same MS-13 conspiracy. Zelaya,
336 Fed. Appx. at 358. Although the decision in Zelaya is not
binding, given that it involved the same witnesses and the
same underlying conspiracy, we find it persuasive.

   Here, the government explained to Ramos-Cruz and the
district court its concerns regarding the danger to El Salvado-
rian citizens who testify against MS-13 members in U.S.
courts. It also disclosed the substance of the testimony the two
witnesses in question would provide at trial. Notably, that tes-
timony did not involve Ramos-Cruz or his activities. Rather,
it provided generalized information about the operation of
MS-13. The government further submitted in camera affida-
vits from both witnesses explaining the specific threat to them
were their identities revealed. Because these affidavits were
originally sworn in 2006 and 2007, the district court con-
ducted an ex parte hearing and examined the two El Salvado-
22               UNITED STATES v. RAMOS-CRUZ
rian officers to determine whether disclosure of their names,
addresses, or dates and places of birth to the defendant would
continue to pose a danger to the officers and their families. It
concluded that the same threat existed that had persuaded it
to permit the officers to testify under these circumstances in
Zelaya.

   After a review of the sealed affidavits and the sealed tran-
script of the ex parte hearing, we cannot say that this decision
was an abuse of discretion. As in Zelaya, "[t]he information
provided to the district court indicated that the threat to these
witnesses and their families, should their true identities be
provided, was ‘actual and not a result of conjecture.’" Id.
(quoting Palermo, 410 F.2d at 472). Moreover, as we also
noted in Zelaya, because "the government disclosed to the
defense details of these two witnesses" before the trial, the
defendants were able to "effectively cross-examine the wit-
nesses without threatening their safety." Id.

   Ramos-Cruz contends that the threats against the two wit-
nesses were too speculative to warrant the protective action
taken by the district court. He points to the fact that Ramos-
Cruz is not himself accused of threatening the witnesses and
argues that "[i]t is not sufficient to assert that anyone who tes-
tifies against one of its members faces danger from MS-13."
Appellant’s Br. 45. With regard to his first point, we agree
with the D.C. Circuit that "[t]he appropriateness of using
pseudonyms to protect witnesses does not depend on whether
the threat to the witness comes directly from a defendant or
from another source." United States v. Celis, 608 F.3d 818,
832 (D.C. Cir. 2010), cert. denied 131 S. Ct. 620 (2010). As
to the second, we do not dispute that such a generalized state-
ment would be insufficient to show that a threat against a wit-
ness was "actual and not a result of conjecture." Palermo, 410
F.2d at 472. The witnesses here, however, specifically
explained the heightened level of danger to which El Salvado-
rians who testify against MS-13 in U.S. courts are subject.
They then connected that threat to the specific investigative
                 UNITED STATES v. RAMOS-CRUZ                  23
work they perform in El Salvador. We believe that this level
of specificity is sufficient.

   Finally, we reiterate the limited focus of the witnesses’ tes-
timony. They proffered no evidence directly involving
Ramos-Cruz or his activities. They merely provided back-
ground information about the internal workings of MS-13
generally. On these facts, we cannot conclude that the district
court abused its discretion.

                               D.

   Ramos-Cruz’s final contention is that the district court
erred by denying his pretrial motion to suppress the evidence
obtained during the August 17, 2004 search of his residence.
He contends that the search warrant was not supported by
probable cause and that officers violated the knock-and-
announce rule. We examine each of these claims in turn.
When evaluating a district court’s denial of a motion to sup-
press, "we review the district court’s factual findings for clear
error and its legal determinations de novo." United States v.
Perry, 560 F.3d 246, 251 (4th Cir. 2009).

                               1.

   A Maryland state court judge issued a search warrant for
Ramos-Cruz’s residence based on an affidavit submitted by
Detective Murphy, a gang unit detective with the RAGE task
force. Ramos-Cruz contends that this affidavit contained little
more than bare assertions and did not provide the issuing
judge with a proper basis to determine that evidence of a
crime would be found at the location named. We disagree.

   "A police officer seeking the issuance of a search warrant
must present an affidavit containing facts sufficient to provide
the [judge] with a substantial basis for determining the exis-
tence of probable cause." Doe v. Broderick, 225 F.3d 440, 451
(4th Cir. 2000) (internal quotation marks omitted). Probable
24               UNITED STATES v. RAMOS-CRUZ
cause exists when "there are reasonably trustworthy facts
which, given the totality of the circumstances, are sufficient
to lead a prudent person to believe that the items sought con-
stitute fruits, instrumentalities, or evidence of crime and will
be present at the time and place of the search." United States
v. Suarez, 906 F.2d 977, 984 (4th Cir. 1990). We afford a
judge’s finding of probable cause "great deference on
review." Id.

   The affidavit Murphy presented here supported the judge’s
finding of probable cause. Murphy sought to search Ramos-
Cruz’s home for evidence of malicious destruction of prop-
erty. In support, he described a photograph of an individual
painting graffiti depicting an MS-13 hand symbol and the
name "Taylor"; he also included a copy of the photograph. He
stated that the person in the photograph was "known to" Ser-
geant Norris, a fellow member of the RAGE task force, as
Ramos-Cruz, alias "Taylor." S.J.A. 5. He explained that the
RAGE task force knew Ramos-Cruz to be a member of the
Sailors. Murphy further stated that, based on his six years of
police experience, persons who create graffiti typically keep
materials at their residences. Finally, Murphy specifically
stated that Ramos-Cruz resided at the address Murphy sought
to search and that Norris had seen Ramos-Cruz entering and
exiting the residence while conducting surveillance of this
location.

   Ramos-Cruz argues that the affidavit stated no basis for the
conclusion that the person in the photograph was Ramos-
Cruz, that his alias was "Taylor," or that he was a member of
MS-13. Appellant’s Br. 24. On the contrary, the affidavit
clearly states the basis for these assertions: Murphy’s col-
league Norris’s experience as a member of the RAGE task
force. Because "[o]bservations of fellow officers . . . engaged
in a common investigation are plainly a reliable basis for a
warrant," United States v. Ventresca, 380 U.S. 102, 111
(1965), Norris’s observation was sufficient. Ramos-Cruz also
contends that there was no basis for determining evidence of
                   UNITED STATES v. RAMOS-CRUZ                        25
property destruction would be found at his residence. Murphy
made this assertion based upon his six years of experience
dealing with gangs and graffiti, and common sense supports
it. Especially given our deferential standard of review, we do
not see any ground for finding that the affidavit did not sup-
port a finding of probable cause.8

                                   2.

   Lastly, Ramos-Cruz alleges that police officers failed to
knock and announce their presence before entering his resi-
dence, and he contends that this alleged oversight warrants
application of the exclusionary rule. Although he chose to
raise it in his brief before us, Ramos-Cruz himself acknowl-
edged the futility of this argument when he withdrew it before
the district court. Without deciding whether the officers vio-
lated the rule, we reiterate that in Hudson v. Michigan, the
Supreme Court held that the exclusionary rule does not apply
to knock-and-announce violations. 547 U.S. at 599. Because
there is clear, binding precedent barring the remedy Ramos-
Cruz seeks, his argument has no merit.

                                  III.

     For the foregoing reasons, the judgment of the district court
is

                                                         AFFIRMED.

FLOYD, Circuit Judge, concurring in part and concurring in
the judgment:

     One of the issues we address today is whether, consistent
     8
     The government argues that, even if the warrant was not supported by
probable cause, the officers who searched Ramos-Cruz’s home relied upon
it in good faith. Because the affidavit supported a finding of probable
cause, we need not reach this argument.
26                 UNITED STATES v. RAMOS-CRUZ
with the Sixth Amendment, the government may convict a
criminal defendant through the use of anonymous witness-
es—that is, witnesses who testify using pseudonyms and
whose true names remain unknown to the defense. I think not.
Thus, I write separately because, in my opinion, the district
court erred when it allowed two of the government’s wit-
nesses to testify using pseudonyms without requiring that the
government disclose their true names to the defense. But,
because the error was harmless, I would nevertheless affirm
the judgment of the district court.

                                    I.

                                   A.

   The right to cross-examination, which the Sixth Amend-
ment guarantees,1 is essential to ensuring that criminal defen-
dants receive a fair trial. See Pointer v. Texas, 380 U.S. 400,
404-05 (1965). The Supreme Court has long recognized that
"[t]here are few subjects, perhaps, upon which this Court and
other courts have been more nearly unanimous than in their
expressions of belief that the right of confrontation and cross-
examination is an essential and fundamental requirement for
the kind of fair trial which is this country’s constitutional
goal." Id. at 405.

  Cross-examination is, practically speaking, one of the most
valuable tools a criminal defendant has to contest the govern-
ment’s case, for it is the primary means through which he may
challenge a witness’s testimony against him. See Davis v.
Alaska, 415 U.S. 308, 316 (1974). Through effective cross-
examination, the criminal defendant may ferret out falsehoods
and expose inconsistencies in a witness’s testimony, see
  1
   Although the Sixth Amendment does not explicitly mention the right
to cross-examination, the Supreme Court has recognized that the right of
confrontation includes the ancillary right of cross-examination. See Davis
v. Alaska, 415 U.S. 308, 315 (1974).
                 UNITED STATES v. RAMOS-CRUZ                  27
Pointer, 380 U.S. at 404, as well as challenge the witness’s
perceptions and memory, Davis, 415 U.S. at 316. Cross-
examination further provides the defendant with the opportu-
nity to impeach the witness’s credibility by demonstrating
bias, prejudice, or ulterior motive, or by revealing facts about
the witness that suggest an untruthful disposition. See id. In
short, the right to confront and cross-examine witnesses "en-
sure[s] the reliability of the evidence against a criminal defen-
dant by subjecting it to rigorous testing in the context of an
adversary proceeding before the trier of fact." Maryland v.
Craig, 497 U.S. 836, 845 (1990).

   Yet the importance of cross-examination in a criminal trial
extends beyond the practical benefits it confers upon the
defendant. The availability of meaningful cross-examination
also fosters society’s perception that criminal trials are open
and fair. Lee v. Illinois, 476 U.S. 530, 540 (1986). It does so
by "ensuring that convictions will not be based on the charges
of unseen and unknown—and hence unchallenge-
able—individuals." Id. If safeguarded, it reflects that, in a
court of law, criminal trials are even contests between the
government and the accused. See id.

   Criminal defendants do not have free rein on cross-
examination, however. The Sixth Amendment "guarantees an
opportunity for effective cross-examination, not cross-
examination that is effective in whatever way, and to what-
ever extent, the defense may wish." Delaware v. Fensterer,
474 U.S. 15, 20 (1985). Trial judges thus possess "wide lati-
tude . . . to impose reasonable limits on . . . cross-examination
based on concerns about, among other things, harassment,
prejudice, confusion of the issues, the witness’[s] safety, or
interrogation that is repetitive or only marginally relevant."
Delaware v. Van Arsdall, 475 U.S. 673, 679 (1986); see also
Chavis v. North Carolina, 637 F.2d 213, 226 (4th Cir. 1980)
(recognizing the trial court’s discretion to limit cross-
examination for many of the same reasons). Because we
entrust trial judges with such discretion, we review a trial
28               UNITED STATES v. RAMOS-CRUZ
court’s limitations on a criminal defendant’s cross-
examination for an abuse of discretion. United States v. Smith,
451 F.3d 209, 220 (4th Cir. 2006).

                              B.

   The Supreme Court, in Smith v. Illinois, 390 U.S. 129
(1968), confronted the issue of whether a trial court may pro-
hibit a criminal defendant from inquiring on cross-
examination as to the true name of the witness testifying
against him. The defendant was charged with, and ultimately
convicted of, illegally selling narcotics. Id. at 129. The pri-
mary witness against him was a man who identified himself
as "James Jordan." Id. at 130. The witness claimed to have
purchased narcotics from the defendant, and the case hinged
in large part on whose story the jury believed: the witness’s
or the defendant’s. Id. On cross-examination, the witness
admitted that James Jordan was not his real name. Id. The
defense attorney then asked the witness what his true name
was, but before the witness could answer, the government
objected. Id. The trial court sustained the objection, forbid-
ding the defense attorney from inquiring as to the witness’s
true name. Id. On appeal, the Appellate Court of Illinois
affirmed the defendant’s conviction. Id. at 129.

   The Supreme Court held that the trial court’s prevention of
the defense attorney from inquiring into the witness’s true
name violated the defendant’s Sixth Amendment right to
cross-examination. Id. at 133. Although the Court recognized
that the case did not involve the "complete denial of all right
of cross-examination," it observed that "when the credibility
of a witness is in issue, the very starting point in ‘exposing
falsehood and bringing out the truth’ through cross-
examination must necessarily be to ask the witness who he is
and where he lives." Id. at 131 (footnote omitted) (quoting
Pointer, 380 U.S. at 404). It then noted that "[t]he witness’[s]
name and address open countless avenues of in-court exami-
nation and out-of-court investigation." Id. It concluded that
                 UNITED STATES v. RAMOS-CRUZ                  29
"[t]o forbid this most rudimentary inquiry at the threshold is
effectively to emasculate the right of cross-examination
itself." Id.

   Justice White authored a concurrence, which Justice Mar-
shall joined, advocating that the personal safety of witnesses
was a proper reason to limit cross-examination. Id. at 133-34
(White, J., concurring). He maintained that, before barring a
question that is normally appropriate, courts should require
either the government or the witness to demonstrate why the
witness should not have to answer it. Id. at 134. According to
Justice White, the trial court could "then ascertain the interest
of the defendant in the answer and exercise an informed dis-
cretion in making his ruling." Id. Ultimately, he concluded
that, in the case presented, neither the State nor the witness
had made any showing to justify allowing the witness to
refuse to provide his name. Id.

   Many courts have since seized upon Justice White’s con-
cerns and held that Smith does not compel a rigid rule of dis-
closure of a witness’s true name and address when it would
pose a threat to the witness’s safety. See, e.g., United States
v. El-Mezain, No. 09-10560, 2011 WL 6058592, at *9 (5th
Cir. Dec. 7, 2011); Siegfriedt v. Fair, 982 F.2d 14, 17 (1st Cir.
1992); United States v. Rangel, 534 F.2d 147, 148 (9th Cir.
1976); United States v. Palermo, 410 F.2d 468, 472 (7th Cir.
1969); People v. Stanard, 365 N.E.2d 857, 863 (N.Y. 1977).
But at least one of these courts has indicated trepidation when
it is the witness’s true name that the government seeks to
withhold. See Palermo, 410 F.2d at 472 ("Under almost all
circumstances, the true name of the witness must be dis-
closed."). Furthermore, not all courts have allowed the gov-
ernment to completely withhold the true names of witnesses
from the defense, even when the safety of the witnesses was
in danger. See, e.g., United States v. Celis, 608 F.3d 818, 829-
30 (D.C. Cir. 2010) (describing a district court’s protective
order that allowed witnesses to testify using pseudonyms but
required disclosure of their true names to defense counsel);
30               UNITED STATES v. RAMOS-CRUZ
Alvarado v. Superior Court, 5 P.3d 203, 223 (Cal. 2000)
("[W]hen nondisclosure of the identity of a crucial witness
will preclude effective investigation and cross-examination of
that witness, the [C]onfrontation [C]lause does not permit the
prosecution to rely upon the testimony of that witness at trial
while refusing to disclose his or her identity.").

   These latter courts often utilize or advocate protective
orders as a means of balancing the criminal defendant’s right
to cross-examine a witness with the need to protect the wit-
ness’s safety. See Celis, 608 F.3d at 829-30 (approving the
district court’s use of a protective order); Alvarado, 5 P.3d at
206 ("[W]e emphasize that the trial court remains free to fash-
ion a more limited order denying, restricting, or deferring dis-
closure of the identity of each witness before trial (including
limiting disclosure to defendants’ counsel), as long as that
order does not impermissibly impair defendants’ right to con-
front and cross-examine the witnesses effectively at trial.").
For example, in Celis, the district court entered a protective
order that allowed witnesses to testify using pseudonyms, but
required the government to release their true names to defense
counsel. Celis, 608 F.3d at 829. The order further provided
that defense counsel could, in turn, share the names with the
represented defendants and one other member of the defense
team, but it prohibited sharing the names with anyone else
without leave of the court. Id. During the trial, the district
court allowed defense counsel to perform limited investiga-
tions of some of the witnesses in Colombia and postponed
cross-examination in at least one instance to allow for an
authorized investigation. Id. at 830. The D.C. Circuit
approved this practice, determining that it appropriately bal-
anced the defendants’ right to cross-examination with the
need to protect the safety of the witnesses. See id. at 833-34.
                   UNITED STATES v. RAMOS-CRUZ                        31
                                   II.

                                  A.

   I do not take lightly the safety concerns accompanying the
decisions made by Juan Diaz and Jose Perez—the two wit-
nesses who testified using pseudonyms2—to testify against
Ramos-Cruz. As the record reflects, MS-13 has demonstrated
its willingness to engage in violent reprisal against witnesses
who testify against its members. There is no denying that by
agreeing to testify against Ramos-Cruz, Diaz and Perez
exposed themselves to danger. Most assuredly, requiring them
to state their true names in open court would have made it
easier for MS-13 to target them and their families. Safety con-
cerns were thus real and valid.

   We must recognize, however, that these concerns inhere in
many prosecutions of defendants who are members of violent
criminal organizations. The sad truth is that, in this respect,
the situation presented in today’s case is not rare. Gangs often
employ violence as a means of intimidating witnesses. Laura
Perry, Note, What’s in a Name?, 46 Am. Crim. L. Rev. 1563,
1580 (2009); Joan Comparet-Cassani, Balancing the Anonym-
ity of Threatened Witnesses Versus a Defendant’s Right of
Confrontation: The Waiver Doctrine After Alvarado, 39 San
Diego L. Rev. 1165, 1194-96 (2002). Witness intimidation is
a serious problem of an alarming magnitude, and it plagues
many of our communities. See Alvarado, 5 P.3d at 222 &
n.14; Comparet-Cassani, supra, at 1194-204. As a result, the
prosecution of members of violent gangs—such as this prose-
cution of Ramos-Cruz—will often trigger safety concerns for
many of the witnesses involved.
  2
   I refer to the witnesses using their pseudonyms throughout my opinion.
32               UNITED STATES v. RAMOS-CRUZ
                               B.

   Nevertheless, in addressing these concerns, we cannot
undermine our constitutional commitment to ensuring that
criminal defendants, even those accused of belonging to vio-
lent criminal organizations, receive a fair trial. That means
they must be allowed to rigorously test the government’s evi-
dence, including all of its witnesses, in an adversarial pro-
ceeding before a jury. See Craig, 497 U.S. at 845; See
Strickland v. Washington, 466 U.S. 668, 685 (1984). I am
unconvinced that they are able to do so if the government can
completely withhold the true names of its witnesses through-
out the trial.

   Access to the true names of the government’s witnesses is
critical to ensuring that a criminal defendant is able to rigor-
ously test their testimony in an adversarial manner. As noted,
effective cross-examination often entails challenging the wit-
ness’s credibility. Hence, the opportunity for effective cross-
examination, which the Sixth Amendment guarantees,
includes the opportunity to challenge the witness’s credibility.
See Van Arsdall, 475 U.S. at 679-80. But without a govern-
ment witness’s true name, the criminal defendant is unable to
perform the type of investigation—whether in court or out of
court—necessary to be able to challenge his credibility. See
Smith, 390 U.S. at 131. The criminal defendant cannot
explore the witness’s background and qualifications to dis-
cover any facts that might reflect poorly on his credibility. See
Alvarado, 5 P.3d at 221. In effect, denying a criminal defen-
dant knowledge of the true names of the government’s wit-
nesses severely inhibits his ability to perform what is often the
most potent aspect of effective cross-examination: impeach-
ment. In my opinion, because completely forbidding a crimi-
nal defendant from learning a witness’s true name prevents
the opportunity for effective cross-examination, it denies the
defendant a fundamental aspect of a fair trial.

  My concerns with completely denying criminal defendants
access to the true names of the witnesses testifying against
                     UNITED STATES v. RAMOS-CRUZ                           33
them extend beyond practical consequences. Allowing the use
of anonymous witnesses also undermines the perception that
our criminal trials are open and even contests. Instead, it
creates the impression that our criminal trials contain clandes-
tine aspects that operate to provide the government with an
upper hand. It does so by suggesting that convictions can be
"based on the charges of . . . unknown—and hence unchal-
lengeable—individuals," Lee, 476 U.S. at 540, even if they
can be physically seen. Simply put, obtaining a conviction by
using anonymous witnesses appears eerie and covert, and
does not inspire confidence in the promise that our criminal
trials are open and even endeavors.

   Thus, even when safety concerns exist, district courts
should require disclosure of the government’s witnesses’ true
names to the defense, even if the disclosure is limited.3 Along
these lines, I embrace the approach approved by the D.C. Cir-
cuit in Celis. If, for safety reasons, the district court finds it
necessary to allow a witness to testify using a pseudonym in
open court, it should require the government to disclose the
true name of the witness to defense counsel outside of court.
The district court could, in its discretion, fashion a protective
order limiting the extent of further disclosure and determining
at what stage disclosure must occur. This would allow the dis-
trict court to ascertain, on an individualized basis, whether
defense counsel’s proposed avenues of investigation are nec-
   3
     I would not limit this disclosure requirement to crucial witnesses, as at
least one court has, see Alvarado, 5 P.3d at 223. The Sixth Amendment
guarantees criminal defendants the opportunity for effective cross-
examination of all government witnesses, irrespective of their relative
importance to the government’s case. Because, in my opinion, this
requires access to the witnesses’ true names, I would not distinguish
between crucial and noncrucial witnesses. Nor would I limit my disclosure
requirement to instances in which it is clear that the witness’s credibility
will be at issue. A witness’s credibility is always potentially at issue,
depending on what, if anything, the defense learns about the witness. In
fact, the defense needs the witness’s true name to determine whether cred-
ibility will be an issue.
34                 UNITED STATES v. RAMOS-CRUZ
essary to ensure the opportunity for effective cross-
examination and whether they would unduly expose the wit-
ness to danger. In my mind, this approach strikes an appropri-
ate balance between a criminal defendant’s right to a fair trial
and the safety concerns accompanying some witnesses’ testi-
mony. It does not sacrifice one to the other.

   Because the district court allowed Perez and Diaz to testify
using pseudonyms and completely denied the defense access
to their true names, I think it abused its discretion. Ramos-
Cruz, without access to Diaz’s and Perez’s true names, was
unable to conduct any meaningful inquiry into their back-
grounds or qualifications. This strikes me as especially prob-
lematic with respect to Diaz, who the district court allowed to
testify as an expert on MS-13 in El Salvador. By denying
Ramos-Cruz any access to Diaz’s and Perez’s true names, the
district court essentially denied him the opportunity to cross-
examine them in any meaningful manner on facts suggesting
bias, prejudice, ulterior motives, or untruthful disposition. As
a result, I do not think the court provided Ramos-Cruz with
the opportunity to conduct effective cross-examination.

                                  C.

   The government maintains that defense counsel had the
opportunity to conduct effective cross-examination despite
not knowing Diaz’s and Perez’s true names. In so arguing, it
emphasizes the information it provided the defense. For
instance, it notes it supplied defense counsel with the tran-
script of Diaz’s and Perez’s previous testimony. It further
observes it informed defense counsel that the witnesses did
not have any Giglio issues4 and that the district court also
questioned the witnesses about their background during an ex
parte hearing, from which the defense was excluded, to ensure
  4
   In Giglio v. United States, 405 U.S. 150 (1972), the Supreme Court
determined that the government must disclose evidence adversely affect-
ing the credibility of its witnesses. Id. at 153-54.
                 UNITED STATES v. RAMOS-CRUZ                   35
no such issues existed. The government insists that defense
counsel’s suggestion that it could have unearthed impeach-
ment material if provided with the witnesses’ true names is
mere speculation. In light of all of this and the fact that
defense counsel had the opportunity to cross-examine Diaz
and Perez in person, the government contends the limitation
on Ramos-Cruz’s ability to discover their true names was an
appropriate exercise of the district court’s discretion.

   I find this argument, particularly as it relates to the govern-
ment’s and district court’s inquiries into the witnesses’ back-
grounds, unpersuasive. Our method of criminal adjudication
relies upon the "common-law tradition . . . of live testimony
in court subject to adversarial testing," not the civil law
inquisitorial method of "examination in private by judicial
officers." Crawford v. Washington, 541 U.S. 36, 43 (2004);
see also id. at 50 (recognizing that "the principal evil at which
the Confrontation Clause was directed was the civil-law mode
of criminal procedure"). We thus define a fair trial as one in
which the evidence is subject to adversarial testing. Strick-
land, 466 U.S. at 685. But here, the district court and the gov-
ernment investigated Diaz’s and Perez’s backgrounds in
private. They then announced to the defense that the witnesses
had nothing to disclose and, by refusing to provide the wit-
nesses’ true names, effectively prevented defense counsel
from verifying this information. In this respect, what took
place below resembles more the inquisitorial method of exam-
ination than our adversarial method. Because we rely upon the
adversarial method as the hallmark of a fair trial, I am unable
to accept the government’s and district court’s investigations
into the witnesses’ backgrounds as adequate substitutes for
defense counsel’s ability to do the same.

   Nor do I find persuasive the government’s argument that
"[a]ny suggestion that the defense would have unearthed
impeachment material if [it] had learned the witnesses’ identi-
ties is mere speculation." Because the defense does not have
the true names of the witnesses, it is unable, and cannot be
36               UNITED STATES v. RAMOS-CRUZ
expected, to know whether any specific impeachment material
exists. All it can do is speculate. But the government seeks to
justify not turning over the true names because defense coun-
sel can only speculate that impeachment material exists. This
circular reasoning is unappealing to me. Credibility is a poten-
tial issue for every witness, and often the only way to know
whether a witness has credibility issues is to investigate the
witness’s background. We rely on the adversarial method to
reveal credibility issues, which means criminal defendants
must be given the tools essential to doing so.

   Finally, I do not agree with the government that Ramos-
Cruz had the opportunity to conduct effective cross-
examination because it supplied him with the witnesses’ prior
testimony and he was able to confront them in person. This
argument ignores the fact that the opportunity for effective
cross-examination entails not only the ability to question wit-
nesses on the substance of their testimony, but also to
impeach their credibility by demonstrating bias, prejudice,
ulterior motives, or an untruthful disposition. Access to a wit-
ness’s true name is often the essential first step to determining
the existence of such facts that would impugn the witness’s
credibility. I therefore cannot say that Ramos-Cruz had the
opportunity to cross-examine Diaz and Perez effectively when
he was essentially denied the opportunity to impeach their
credibility.

                              III.

  My finding of error does not end the inquiry, however.
Harmless-error analysis applies to unconstitutional limitations
on a criminal defendant’s right to cross-examination. See Van
Arsdall, 475 U.S. at 684. "The correct inquiry is whether,
assuming that the damaging potential of the cross-
examination were fully realized, a reviewing court might
nonetheless say that the error was harmless beyond a reason-
able doubt." Id. To find an error harmless beyond a reason-
able doubt, we must "be able to say with fair assurance, after
                 UNITED STATES v. RAMOS-CRUZ                37
pondering all that happened without stripping the erroneous
action from the whole, that the judgment was not substantially
swayed by the error." United States v. Abu Ali, 528 F.3d 210,
256 (4th Cir. 2008) (quoting United States v. Brooks, 111
F.3d 365, 371 (4th Cir. 1997)) (internal quotation marks omit-
ted). The Supreme Court has set forth a nonexhaustive list of
five factors to guide this inquiry: 1) "the importance of the
witness’[s] testimony in the prosecution’s case"; 2) "whether
the testimony was cumulative"; 3) "the presence or absence of
evidence corroborating or contradicting the testimony of the
witness on material points"; 4) "the extent of cross-
examination otherwise permitted"; and 5) "the overall
strength of the prosecution’s case." Van Arsdall, 475 U.S. at
684.

   Although I think the district court erred in allowing Perez
and Diaz to testify using pseudonyms without any disclosure
of their true names to the defense, I nevertheless would find
the error harmless beyond a reasonable doubt. Even operating
under the assumption that if provided access to Perez’s and
Diaz’s true names Ramos-Cruz would have discovered dam-
aging information that would have allowed him to discredit
their testimony completely, I can safely say with assurance
that the error did not substantially sway the judgment of the
jury.

   Perez and Diaz primarily testified as to the organization of
MS-13 and how MS-13 in El Salvador was linked to MS-13
in the United States to prove that the gang was a criminal
enterprise for purposes of the racketeering charges. Other evi-
dence amply proved it was a criminal enterprise and demon-
strated the link between MS-13 in El Salvador and MS-13 in
the United States. Diaz’s and Perez’s testimony was cumula-
tive and not critical to establishing that MS-13 is a criminal
enterprise. The strength of the government’s case as to this
element was strong. Thus, even if the jury had not given any
weight to Diaz’s and Perez’s testimony, the other evidence
established beyond a reasonable doubt that MS-13 is a crimi-
38               UNITED STATES v. RAMOS-CRUZ
nal enterprise with ties that extend from the United States to
El Salvador.

                              IV.

   For these reasons, I decline to join Part II.C of the majori-
ty’s opinion, but nevertheless join in affirming as to the issue.
Otherwise, I am pleased to concur in the remainder of the
majority’s opinion.
