In the
 United States Court of Appeals
              For the Seventh Circuit
                         ____________

No. 05-4797
UNITED STATES OF AMERICA,
                                               Plaintiff-Appellee,
                                v.

SALEEM LAKE,
                                           Defendant-Appellant.
                         ____________
           Appeal from the United States District Court
      for the Northern District of Illinois, Eastern Division.
      No. 05-CR-169—James F. Holderman, Chief Judge.
                         ____________
 ARGUED OCTOBER 30, 2006—DECIDED SEPTEMBER 5, 2007
                    ____________


 Before KANNE, ROVNER, and WILLIAMS, Circuit Judges.
   ROVNER, Circuit Judge. A jury convicted Saleem Lake
of possessing crack cocaine with intent to distribute, see
21 U.S.C. § 841(a)(1), possessing a firearm as a felon, see
18 U.S.C. § 922(g)(1), possessing a firearm with an altered
serial number, see 18 U.S.C. § 922(k), and possessing a
firearm in relation to drug trafficking, see 18 U.S.C.
§ 924(c)(1)(A). He was sentenced to twenty years’ impris-
onment. On appeal Lake argues that the district court
erred in denying his motion to suppress evidence, and that
the government did not prove beyond a reasonable doubt
that Lake possessed crack. We affirm.
2                                              No. 05-4797

                            I.
  In September 2004, a “concerned citizen” informed
Chicago police officer Stephen Del Bosque that he had
known Saleem Lake for at least ten years, that Lake sold
“rock,” or crack, out of his apartment, and that he had
bought crack from Lake the previous evening. The infor-
mant specified that Lake took the crack from a particular
dresser drawer in his bedroom and that he saw a black
pistol inside that drawer. He then drew a diagram of
Lake’s apartment and highlighted where Lake kept the
contraband. Officer Del Bosque and another officer drove
past Lake’s apartment to confirm that the exterior
matched the informant’s description. It did, and Officer
Del Bosque requested that an Illinois state-court judge
sign a search warrant, which she did after listening to
sworn statements from Officer Del Bosque, two other
officers, and the informant. Upon executing the warrant,
the officers found drugs and a gun, and they arrested
Lake. In February 2005, the grand jury indicted Lake on
the four previously-mentioned charges; he pleaded not
guilty.
  Before trial Lake moved to suppress the gun and drugs
found in his bedroom, arguing that the search warrant
was not based on probable cause. The district court held
a hearing on Lake’s motion. At the hearing, the govern-
ment called two witnesses: the officer who obtained the
warrant and the state-court judge who issued it. Officer
Del Bosque testified that the informant told officers that
Lake sold crack from his apartment and the informant
specified the location of the drugs. Officer Del Bosque also
testified to meeting with the state-court judge, other
officers, and the informant to secure a search warrant.
According to Officer Del Bosque, the judge only signed the
warrant after swearing in and questioning both the
informant and the officers. For her part, the state-court
judge testified that, although she could not remember
No. 05-4797                                              3

this particular warrant, her general practice was to speak
with the officers as well as the individual supplying
information for the warrant and to have all parties
sign the warrant. She also testified that she always
questioned informants who appeared before her. When
asked why the warrant in this case was not signed by the
informant, the judge admitted that she had made a
mistake.
  Lake began by calling the informant to the stand, but,
asserting his Fifth Amendment privilege against self-
incrimination, the informant refused to answer questions.
The district court asked the government whether it
would grant immunity to the informant, but the govern-
ment refused because, it argued, the officers were avail-
able as witnesses and the only relevant question was
whether the officers reasonably believed the informant’s
statements. Additionally (as we discuss below), the
government had reason to doubt the veracity of the infor-
mant’s testimony. Agent Raphael Uribe of the Bureau of
Alcohol, Tobacco, and Firearms next testified that during
a July 2005 meeting with an assistant U.S. attorney and
various others, the informant changed his initial story. He
denied having told police that he bought crack from Lake
and that he had seen a gun in Lake’s apartment. But on
cross-examination, Agent Uribe also testified that the
informant apparently was beaten up after he told police
about Lake’s illegal activities. The government suggested
that the beating may have affected the informant’s will-
ingness to cooperate.
  Lake then renewed his motion to suppress the gun and
drugs found in his bedroom. The district court acknowl-
edged that the circumstances surrounding the issuance of
the warrant were somewhat troubling because the infor-
mant changed his story and then asserted his Fifth
Amendment rights, giving Lake no opportunity to cross-
examine him, and because the state-court judge could not
4                                              No. 05-4797

explain why the informant had not signed the warrant.
Nonetheless, the district court found that the officers
reasonably relied on the informant’s statements and that
a reasonable judicial officer would have found probable
cause given the evidence presented to her.
  The government charged Lake with possessing crack,
which carries higher penalties than other forms of cocaine,
so at trial it had to specifically prove that Lake possessed
crack. To this end, the government called four witnesses.
Both a forensic scientist who specialized in analyzing
controlled substances and a forensic chemist testified
that the “white rocky substance” found in Lake’s bedroom
tested positive for cocaine base. On cross-examination, the
chemist admitted that Lake’s drugs did not contain sodium
bicarbonate (baking soda), which is often used to prepare
crack. But he explained that a person could produce crack
without leaving traces of sodium bicarbonate in the
finished product. Next, a lieutenant from the Drug En-
forcement Administration testified that the drugs found
in Lake’s possession were crack. Finally, a self-described
“crack-head” testified that Lake gave him crack “from
time to time.”
  At the close of trial in July 2005, the jury found Lake
guilty on all counts. The jury also returned a special
verdict finding that Lake possessed crack. In November
2005, the district court sentenced Lake to a total of twenty
years’ imprisonment.


                            II.
  On appeal Lake advances three arguments: (1) the
district court should have granted his motion to suppress
the gun and drugs found in his bedroom, (2) the govern-
ment violated his due process rights by refusing to grant
immunity to the informant, and (3) the government did not
No. 05-4797                                                 5

prove beyond a reasonable doubt that the drugs were
crack.


                             A.
  Lake claims that the gun and drugs should have been
suppressed because the search warrant used to enter his
apartment was not supported by probable cause. We
review the denial of a motion to suppress de novo for
questions of law, but for clear error as to questions of fact.
See United States v. Shoals, 

, 852 (7th Cir.
2007). The district court’s probable cause determination
is reviewed de novo. See United States v. Spry, 

, 835 (7th Cir. 1999). Probable cause for a search
warrant exists where the known facts and circumstances
are sufficient for a reasonably prudent person to form the
belief that contraband or evidence of a crime will be found.
See United States v. Olson, 

, 370 (7th Cir.
2005).
  The known facts and circumstances in this case support
a finding of probable cause. The informant told police that
he had bought drugs from Lake in Lake’s apartment the
previous evening. He also drew a diagram of the apart-
ment and specified exactly where Lake kept the drugs.
Officers then drove past Lake’s apartment and verified
the accuracy of at least some of the information the
informant gave them. As an initial matter, the level of
detail provided by the informant supports the probable
cause finding. See United States v. Brack, 

,
756 (7th Cir. 1999). Additionally, the informant’s admis-
sion that he had purchased crack is a statement against
his penal interest and thus a weighty factor in establishing
probable cause even if the statements have not been
proven reliable. See United States v. Brown, 

,
459-60 (7th Cir. 2004). Lake makes much of the fact that
this informant was previously unknown to police, but he
6                                              No. 05-4797

had bought the crack from Lake the night before he spoke
to police and, given the recency of the purchase, it was
reasonable for the police to rely on his statements. Com-
pare United States v. Harju, 

, 603, 609-11 (7th
Cir. 2006) with Owens v. United States, 

, 608
(7th Cir. 2004). Finally, although the informant later
changed his story, the validity of a warrant is judged on
the basis of information available at the time the warrant
was issued. See Maryland v. Garrison, 

, 84-86
(1987); United States v. White, 

, 637-38 (7th
Cir. 2005).
  The district court’s probable cause finding was further
supported by the fact that the informant was presented to
the state-court judge before the warrant was issued, and
the judge had the opportunity to assess his credibility.
According to her testimony at the suppression hearing, the
state-court judge’s practice was to require officers and the
informant to appear personally before her for question-
ing before she issued warrants. The judge’s testimony
was supported by Officer Del Bosque, who also described
meeting with the judge, informant, and other officers to
acquire the search warrant. Additionally, even though the
informant later disavowed telling officers that he saw
drugs in Lake’s apartment, according to Agent Uribe’s
testimony, the informant acknowledged having met with
the state-court judge and officers on the night the
search warrant was signed, and the state-court judge
testified that she always questioned informants who came
before her. Accordingly, there was enough evidence to
support a finding that the judge assessed the informant’s
credibility, which is an important factor in determining
whether probable cause is established on the basis of an
informant’s tip. See United States v. McGaughy, 

, 970 (7th Cir. 2007). Because there was probable cause
for the warrant, the district court properly denied Lake’s
motion to suppress.
No. 05-4797                                                 7

                             B.
  Lake next argues that the government’s refusal to grant
immunity to the informant during the suppression hearing
prevented him from challenging whether probable cause
existed for the search warrant, thus depriving him of due
process. We will not review decisions regarding immunity
unless substantial evidence shows that the government’s
action was a clear abuse of discretion that violated the
due process clause. See United States v. Schweihs, 

, 1315 (7th Cir. 1992). Prosecutors have signifi-
cant discretion to decline immunity to a witness, especially
when it is likely that the witness will perjure himself. See,
e.g., United States v. Burke, 

, 411 (7th Cir.
2005); United States v. Hooks, 

, 802 (7th Cir.
1988). In this case, the informant initially told the officers
that he had seen drugs in Lake’s apartment, but later
retracted his statements. Not surprisingly, the govern-
ment doubted that the informant’s testimony would be
truthful, and the government’s “refusal to absolve wit-
nesses of their responsibility to testify truthfully does not
impermissibly distort the fact-finding process.” 

. We therefore conclude that Lake’s due
process rights were not violated by the government’s
decision not to grant immunity.


                             C.
  Finally, Lake argues that the government did not prove
beyond a reasonable doubt that he possessed crack. The
jury that convicted Lake found that the substance was
crack, and we will overturn that determination only if the
record contains no evidence from which a rational jury
could have returned the finding. See United States v.
James, 

, 705 (7th Cir. 2006). In this case, in
addition to the chemist and forensic scientist who testified
that the substance contained cocaine base, a DEA lieuten-
8                                               No. 05-4797

ant and, perhaps more importantly, a former crack user
identified the drugs as crack. See United States v. Bradley,

, 595-96 (7th Cir. 1999) (“[T]hose who smoke,
buy, or sell this stuff are the real experts on what is
crack.”). Lake cites United States v. Edwards, 

, 572 (7th Cir. 2005), to argue that the drugs found in
his possession could not be crack because they did not
contain sodium bicarbonate, but Lake misreads our
precedent. Although we observed in Edwards that crack
is “the street name for a form of cocaine base, usually
prepared by processing cocaine hydrochloride and sodium
bicarbonate, and usually appearing in a lumpy, rocklike
form,” 

we did not mandate that a
substance must contain those ingredients to be crack. We
have previously held that the testimony of both a forensic
chemist and a veteran police officer is sufficient proof that
a substance is crack. See United States v. Buchanan, 

, 413 (7th Cir. 2004); United States v. Linton, 

, 329-30 (7th Cir. 2000). Accordingly, we conclude
that the testimony of the officer and others in this
case constituted enough evidence for a rational jury to
conclude that Lake possessed crack.


                            III.
  For the reasons stated above, the judgment of the
district court is AFFIRMED.

A true Copy:
      Teste:

                        ________________________________
                        Clerk of the United States Court of
                          Appeals for the Seventh Circuit

                   USCA-02-C-0072—9-5-07