                               In the

    United States Court of Appeals
                 For the Seventh Circuit
                     ____________________
No. 17-1833
UNITED STATES OF AMERICA,
                                                   Plaintiff-Appellee,
                                 v.

ERIC CURTIS,
                                               Defendant-Appellant.
                     ____________________

         Appeal from the United States District Court for the
           Northern District of Illinois, Eastern Division.
           No. 13 CR 952-2 — Charles P. Kocoras, Judge.
                     ____________________

    ARGUED MARCH 27, 2018 — DECIDED AUGUST 24, 2018
               ____________________

   Before WOOD, Chief Judge, and BAUER and KANNE, Circuit
Judges.
    WOOD, Chief Judge. Eric Curtis led a crew that robbed five
cell-phone stores located in suburban Chicago. He was ar-
rested following the last of the heists and eventually stood
trial on ten criminal charges: four counts for robbery, four
counts for aiding in the brandishing of a firearm in relation to
a crime of violence, a count for conspiracy, and a count for
being a felon in possession of a firearm. A jury convicted him
2                                                   No. 17-1833

on all counts save two: one for robbery and one for aiding in
the brandishing of a firearm. Each acquittal was on a charge
related to a robbery of a store in Joliet.
    Curtis raises two issues on appeal. First, he argues that the
district court should have excluded evidence of his cell-site
location information (“CSLI”), which he alleges was obtained
in violation of the Fourth Amendment. Second, he complains
that the district court prohibited him from cross-examining
witnesses about a potential source of bias, and thereby vio-
lated the Sixth Amendment’s Confrontation Clause. Neither
of these alleged errors is enough to disturb the judgment
against him, which we aﬃrm.
                                I
    “CSLI is location information generated by cellular phone
providers that indicates which cell tower a particular phone
was communicating with when a communication was made.”
Orin S. Kerr, The Eﬀect of Legislation on Fourth Amendment Pro-
tection, 115 MICH. L. REV. 1117, 1128 (2017). It is capable of
“pinpoint[ing] a phone’s location within 50 meters.” Carpenter
v. United States, 138 S. Ct. 2206, 2219 (2018). Because cell
phones are in constant communication with the nearest
cell site—often aﬃxed to a cell tower—they can collect CSLI
as frequently as several times a minute. Id. at 2211–12. In this
case, the government obtained historical CSLI for Curtis’s cell
phone for a span of 314 days. The data placed Curtis in the
vicinity of four of the five stores at the time each was robbed.
There was no CSLI evidence for the Joliet robbery.
   The government relied on the procedures set forth in the
Stored Communications Act (SCA), 18 U.S.C. § 2703, to obtain
Curtis’s CSLI. The type of data it sought is considered to be
No. 17-1833                                                    3

non-content information for SCA purposes. See 18 U.S.C.
§ 2703(c). That part of the SCA authorizes courts to order cell-
phone providers to disclose non-content information if the
government “oﬀers specific and articulable facts showing that
there are reasonable grounds to believe that … the records or
other information sought are relevant and material to an on-
going criminal investigation.” 18 U.S.C. § 2703(c)(1)(B), (d).
Curtis did not dispute the government’s compliance with the
SCA, but he took the position that SCA compliance was not
enough and moved to suppress the evidence. He argued that
collecting CSLI without a search warrant violates the Fourth
Amendment because there is a reasonable expectation of pri-
vacy in CSLI. The district court denied the motion, ruling that
a cell-phone user voluntarily discloses CSLI to his phone pro-
vider, and that the Fourth Amendment does not protect vol-
untarily disclosed information. See Smith v. Maryland, 442 U.S.
735, 743–44 (1979); United States v. Miller, 425 U.S. 435, 442–44
(1976). Curtis appeals that ruling.
    The Supreme Court resolved Curtis’s Fourth Amendment
argument in Carpenter v. United States, 138 S. Ct. 2206 (2018).
There it decided that a person in Curtis’s position, for whom
data was collected for a substantial time, maintains a legiti-
mate expectation of privacy for Fourth Amendment purposes
in the records of his physical movements disclosed by CSLI.
See id. at 2217. It declined to say whether there was “a limited
period for which the Government may obtain an individual’s
historical CSLI free from Fourth Amendment scrutiny,” de-
ciding only that accessing seven days’ or more worth of infor-
mation was enough. Id. at 2217 n.3. In Carpenter, as here, the
prosecutors had obtained court orders under the SCA, and
those court orders purported to authorize the collection of the
target’s cell phone records. Id. at 2212. The Court said that
4                                                    No. 17-1833

SCA compliance did not matter, because the showing re-
quired by the SCA “falls well short of the probable cause re-
quired for a warrant.” Id. at 2221. The Court also rejected the
applicability of the “third-party doctrine,” which (when it ap-
plies) allows the collection of business records collected by a
third party in the ordinary course of operations. Id. at 2217. It
remanded the case for further proceedings.
    Our case stands in the same position as the Carpenter re-
mand. The Court has resolved the question whether an SCA
order obviates the need for the warrant, but it has not spoken
to what should happen next. We must decide whether this
conceded error automatically results in relief for Curtis, for
whom records covering 314 days were collected. We conclude
that it does not. A diﬀerent part of Fourth Amendment juris-
prudence is, in our view, dispositive: evidence obtained in
good-faith reliance on a statute later declared unconstitu-
tional need not be excluded. Illinois v. Krull, 480 U.S. 340, 349–
50 (1987); see also United States v. Pembrook, 876 F.3d 812, 823
(6th Cir. 2017), vacated on other grounds by Johnson v. United
States, 138 S. Ct. 2676 (2018) (applying the good-faith excep-
tion to CSLI obtained under the SCA); United States v. Graham,
796 F.3d 332, 363 (4th Cir. 2015), reversed on other grounds by
United States v. Graham, 824 F.3d 421 (4th Cir. 2016) (en banc)
(same); United States v. Davis, 785 F.3d 498, 511, 518 n.20
(11th Cir. 2015) (same).
    Curtis’s proposed path around Krull is ambitious. He does
not argue that oﬃcers obtained his CSLI in bad faith. Far from
it: his motion to suppress seemingly concedes that there
would have been probable cause to seek a search warrant. It
is Krull itself that he attempts to push out of the picture. He
No. 17-1833                                                      5

argues that Krull applies only to statutes authorizing admin-
istrative searches. His logic proceeds in three steps. First, he
urges, the good-faith exception to the exclusionary rule can-
not be applied so as to insulate statutes from constitutional
challenge. To do so would “destroy[] all incentive on the part
of individual criminal defendants to litigate the violation of
their Fourth Amendment rights.” Krull, 480 U.S. at 369
(O’Connor, J., dissenting). Second, he suggests that the Krull
majority could sidestep that concern because the target of an
administrative search necessarily knows that a search is im-
pending. A forewarned target still has reason to “bring an ac-
tion seeking a declaration that the statute is unconstitutional
and an injunction barring its implementation” notwithstand-
ing the good-faith exception. Id. at 354 (majority opinion).
Third, he points out that the target of an SCA order issued
under section 2703(d) has no knowledge of the order until the
CSLI has been collected and used in a criminal proceeding. At
that late hour, a defendant has no incentive to challenge the
statute because the good-faith exception permits admission of
the fruits of an unconstitutional search.
    Experience has shown that the good-faith exception has
not had the chilling eﬀect that Curtis fears. Curtis, like many
others, has challenged section 2703(d) of the SCA on Fourth
Amendment grounds notwithstanding the risk that the ex-
ception may apply. See, e.g., Carpenter, supra; United States v.
Graham, 824 F.3d 421, 425 (4th Cir. 2016) (en banc); United States
v. Daniels, 803 F.3d 335, 351–52 (7th Cir. 2015); Davis, 785 F.3d
at 511; In re U.S. for Historical Cell Site Data, 724 F.3d 600, 608
(5th Cir. 2013). This is just what the Krull majority predicted:
defendants will still “contest the validity of statutes [even] if
they are unable to benefit directly by the subsequent exclu-
sion of evidence … .” Krull, 480 U.S. at 353.
6                                                     No. 17-1833

    The exclusionary rule is designed primarily to deter un-
constitutional conduct. Id. at 349. Nothing substantiates the
fear that when passing laws such as the SCA “legislators are
inclined to subvert their oaths and the Fourth Amendment.”
Id. at 351. Even if there were a need to deter legislators, “there
is nothing to indicate that applying the exclusionary rule to
evidence seized pursuant to the statute prior to the declara-
tion of its invalidity will act as a significant, additional deter-
rent.” Id. at 352. We conclude, therefore, that even though it is
now established that the Fourth Amendment requires a war-
rant for the type of cell-phone data present here, exclusion of
that information was not required because it was collected in
good faith.
                                II
    The second issue Curtis raises is whether he should have
been allowed to ask witnesses about what happened follow-
ing the first of the five robberies. After that robbery, police
went to the home of Ryan Rogers, Curtis’s cousin, whom po-
lice suspected of organizing the first robbery. A confrontation
ensued, and oﬃcers shot and killed Ryan. (We use his first
name because Eric Rogers also played a role in these events.)
Curtis was a witness. Several hours later, after Curtis had re-
turned home, oﬃcers raided his house. At that time, Curtis
asked for the name of the oﬃcer who had killed Ryan and de-
clared his intent to file a complaint. Eric Rogers, Curtis’s co-
conspirator, was with Curtis while these events transpired.
   On the eve of trial, Curtis asked the court if he would be
permitted to cross-examine Eric, who had become a govern-
ment witness, about the shooting and the ensuing interaction
between Curtis and law enforcement. Cross-examination,
Curtis maintained, would reveal Eric’s motivation to testify
No. 17-1833                                                   7

against him because Eric believed that, given Curtis’s conten-
tious relationship with law enforcement, the authorities
would look with particular favor on any witness who cooper-
ated against Curtis. The district court denied Curtis’s request
without prejudice, ruling that the theory was attenuated and
would lead the trial on a “goose chase.”
    The next day, Curtis filed a written motion seeking per-
mission to cross-examine all coconspirators serving as gov-
ernment witnesses about whether they knew that Curtis had
accused the police of unjustifiably shooting Ryan. In addition
to the theory articulated the day before, Curtis oﬀered two
more reasons why cross-examination would reveal bias. First,
he contended that asking about Curtis’s threat to file a com-
plaint would show that law enforcement had reason to nudge
each witness to turn against Curtis. Second, he argued that
cross-examination would show that witnesses feared the po-
lice because they knew that Ryan had been killed unjustifiably
during the investigation of the robberies at issue. The district
judge remained unmoved, explaining from the bench that
Curtis’s theory was too convoluted and that there already was
an abundance of evidence that the government’s witnesses
were biased. The court also found that bringing up a poten-
tially unjustified shooting would be excessively prejudicial.
Curtis appeals that ruling. He has pared down his argument
at this stage, contending only that the district court should
have permitted the questions to show that the witnesses be-
lieved they would benefit from testifying against Curtis.
    The Sixth Amendment’s Confrontation Clause guarantees
the right to eﬀective cross-examination. United States v. Mar-
tin, 618 F.3d 705, 727 (7th Cir. 2010). Among other things, it
8                                                   No. 17-1833

entitles a defendant to cross-examine a witness about each po-
tential source of bias. Id. But the Confrontation Clause is not
a license to ask a witness literally anything. On the contrary,
trial judges may narrow the scope of questioning for reasons
such as “harassment, prejudice, confusion of the issues, the
witness’ safety, or interrogation that is repetitive or only mar-
ginally relevant.” Delaware v. Van Arsdall, 475 U.S. 673, 679
(1986). If denying Curtis’s desired line of cross-examination
was constitutionally improper, we must vacate the convic-
tions unless we can say beyond a reasonable doubt that after
assuming the full damaging eﬀect of the potential cross-ex-
amination the error was harmless. Id. at 684.
    Curtis made the district court’s job harder than necessary.
He buried his strongest argument—the one raised on ap-
peal—between two theories that were speculative, tenuous,
and required a prejudicial account of the shooting. Even if we
assume, however, that Curtis’s argument was properly
raised, we are convinced beyond a reasonable doubt that any
error, if there was one, was harmless.
    The centerpiece of the case against Curtis was the CSLI
data placing him near four of the robberies, coupled with call
logs exhibiting that Curtis was in communication with admit-
ted participants during each offense. Though the government
induced several of Curtis’s coconspirators to testify against
him, we are convinced that their testimony added little to the
jury’s evaluation of the evidence. Curtis’s attorney effectively
brought out the significant evidence of each witness’s bias.
One by one, the witnesses admitted to having or expecting a
cooperation agreement through which they stood to receive a
sizable sentence reduction in their own criminal case—one
No. 17-1833                                                     9

witness hoped for a reduction of as much as 54 years—in ex-
change for testifying. Some of the witnesses also admitted to
having lied initially to law enforcement about the extent of
their and Curtis’s involvement, minimizing the former and
overstating the latter. The verdict captures the effect of the im-
peachment. Recall that Curtis was acquitted on the two
charges related to the robbery that took place in Joliet and was
convicted on the rest. Joliet was the sole robbery for which the
government did not have CSLI evidence or evidence of what
calls Curtis placed during the robbery. Only witness testi-
mony tied Curtis to the Joliet robbery. The latter, it appears,
was not enough by itself to satisfy the jury.
    Finally, Curtis’s attorney managed to put Ryan’s death
and Curtis’s threatened complaint against the police before
the jury notwithstanding the district court’s adverse ruling.
When an FBI agent took the witness stand, defense counsel
asked him about both. Curtis testified in his own defense and
told the jury that he had witnessed police kill his cousin and
that he and his family were pursuing a complaint against the
police. In his closing argument, defense counsel contended
that there was an implicit conspiracy to frame Curtis. He
asked the jury to recall that “Eric Curtis saw his cousin killed
by the police and he stood up to the police.” And Curtis re-
minded them that he had said to the oﬃcers, “I want to file a
complaint. I saw they killed him for nothing.” Because of this,
defense counsel argued to the jury that “[Curtis] has got a
problem with law enforcement.” Continuing, defense counsel
told the jury that “[Curtis] is the guy who is standing up to
law enforcement. Everybody knew that. And the idea that
they didn’t is nonsense.” While counsel did not say that the
prosecutors directed any witness to testify against Curtis, he
10                                                 No. 17-1833

did suggest that they made witnesses comfortable about turn-
ing on Curtis. Because Curtis made his desired arguments
and impeached his coconspirators, any error in denying the
cross-examination was harmless.
                              III
    Not all constitutional injuries have a remedy. In this case,
good faith renders the Fourth Amendment violation non-re-
dressable, and any Sixth Amendment violations were harm-
less. We therefore AFFIRM the judgment.
