                              In the

United States Court of Appeals
               For the Seventh Circuit

No. 07-2032

U NITED S TATES OF A MERICA,
                                                    Plaintiff-Appellee,
                                  v.

D ARVELL D WAYNE Y ORK,
                                               Defendant-Appellant.


             Appeal from the United States District Court
        for the Northern District of Illinois, Eastern Division.
              No. 04 CR 257—William J. Hibbler, Judge.



       A RGUED A PRIL 17, 2008—D ECIDED JULY 15, 2009




 Before R IPPLE, M ANION, and T INDER, Circuit Judges.
  T INDER, Circuit Judge. As Darvell York spoke to Tracy
Mitchell about selling him “nine probably hard,” law
enforcement was listening. Agents had set up a sting to
buy nine ounces of crack cocaine from York, and Mitchell
was their informant. At York’s trial, the government
played the recorded conversations for the jury. Though
York and Mitchell seemed to speak in plain English,
without any reference to drugs, the government argued
2                                           No. 07-2032

that they were really conversing in the cryptic, coded
language of the narcotics trade. The government called
two law enforcement witnesses to interpret this drug
jargon for the jury. These interpretations made clear
that York and Mitchell were negotiating a drug deal,
despite their words being facially benign—e.g., “nine
probably hard” meant nine ounces of crack cocaine. At
this, York cries foul, stating a slew of reasons why he
believes this interpretation testimony should have been
thrown out. After reviewing the admissibility of each
agent’s testimony, we find that the district court was
correct in admitting the vast majority of the agents’
translations; only a small portion of one agent’s testi-
mony was erroneously admitted. Consequently, the crux
of this case is whether those few errors were harmless.
We conclude that they were and therefore affirm.


                           I.
  On April 30, 2003, law enforcement executed the sting
to buy crack from York. Agents equipped Mitchell with
an audio transmitter and an audio recording device to
monitor in real time and record any of Mitchell’s con-
versations. They gave him $6,500 cash to make the buy.
Mitchell waited for York at a residential jobsite where
Mitchell was supervising a landscaping crew, while a
couple of blocks away agents looked on with binoculars
and a video camera.
  York first showed up in the early afternoon. As he
talked to Mitchell, the covert audio devices picked up
what he had to say:
No. 07-2032                                               3

   MITCHELL:
       . . . . So I was (U/I) going to get a half. You
       know what I’m saying? And then I was gonna
       boost the half up like, cause you can, how
       much can you make off of a half of one?
   YORK:
       I don’t know. It depends on the work you
       know? You still want the shit to be sellable,
       man. You know?
   MITCHELL:
       . . . . Just get you know what I’m saying? Nine,
       nine probably hard right? And then I’ll flip
       that mother fucker and then I’ll come back,
       cause she own [sic] me $20,000 for this. That’s
       all I got left to do right here.
   YORK:
       So what you trying to do now?
   MITCHELL:
       Just got, just bring me nine.
   YORK:
       (U/I) you want me to cook it?
   MITCHELL:
       What, it gonna be soft?
   YORK:
       Huh?
4                                                    No. 07-2032

    MITCHELL:
        It’s gonna be soft?
    YORK:
        (U/I) . . . . I ain’t did nothin’ in a while, I got to
        get another mother fucker to get it though. But
        it gonna be right though.
    MITCHELL:
        Okay. Well, that’s fine. But then I’m be here till
        like eight . . . .
  Mitchell and York then got into Mitchell’s van (which
the police had previously searched for drugs and found
none), and York told Mitchell, “get your money straight,”
and said, “That shit costs, uh, six nigger.” They talked
for a little while longer in the van, making a couple
more references to numbers and money (“five dollar” and
“fifty-five”). Then they got out and York took off in his car.
  Mitchell then rendezvoused with the agents. They
debriefed him and searched his person and his car. They
did not find any drugs, but they did find that Mitchell
had only $500 of the initial $6,500 they gave him. The
agents instructed Mitchell to head back to the jobsite
and wait for York to return. While he waited, a woman
arrived who officers assumed (after checking her car’s
plates) to be Mitchell’s wife. Though the audio transmit-
ter’s battery had died and police could not hear their
conversation, police observed Mitchell hand her what
appeared to be a set of keys. They did not see the
woman give anything to Mitchell.
No. 07-2032                                                 5

  York pulled up around six o’clock that evening and
this time he had somebody else in the car with him.
Mitchell walked over to the passenger side of York’s car
and started talking with York and the other man. Then
York said, “That’s nine right, that’s nine like that, you
wait on it.” The police watched with binoculars and the
video camera, but Mitchell’s position blocked their
view. So the officers could not see whether York handed
something to Mitchell. After Mitchell and York chatted a
bit more about Mitchell’s landscaping job, York left.
Mitchell then circled back with the agents. They searched
him and again found the $500 in cash. This time, how-
ever, they found something else—a clear plastic bag that
contained nine ounces of crack cocaine.
  York was indicted on one count of knowingly and
intentionally distributing cocaine base (specifically crack)
in violation of 21 U.S.C. § 841(a)(1). His first trial ended
without a unanimous verdict, resulting in a mistrial. York
was retried a few months later. The government’s case
was nearly identical at both trials—the same witnesses
testified at each and their testimony was substantially
the same. In neither trial did the informant Mitchell testify.
  At the second trial, the jury heard from a number of
witnesses, including a chemist, a fingerprint expert, and a
set of law enforcement officers. Two of those officers are
of concern in this case. The first was FBI Agent Mike
Brown, who was one of the primary agents handling
the investigation of York and who helped execute the
sting. Brown explained the sting operation to the jury,
described what the jurors saw as they watched the video
6                                               No. 07-2032

of York meeting with Mitchell, and identified the voices
in the audio recordings as Mitchell’s and York’s. He
also said that he heard the sound of money being
counted while eavesdropping when York and Mitchell
were in the van. In addition, Brown described his
meeting with Mitchell in between York’s visits, where
Mitchell had only $500 of the original $6,500, and his
rendezvous with Mitchell after York’s second visit,
where Brown found Mitchell with what looked like
(and was later determined to be) crack cocaine.
  But the government did not use Brown solely as a fact
witness. Brown had extensive experience in prior drug
cases. So the government, without first formally
offering Brown as an expert, asked Brown to give his
opinion about the meaning of certain words and phrases
that Mitchell and York used in their conversations. Brown
obliged: “half” meant half a kilo of cocaine, “nine” meant
nine ounces, “hard” meant crack cocaine, “soft” meant
powder cocaine, “work” meant the drug business, “cook”
meant converting powder cocaine into crack, and “boost
up” meant diluting a given quantity of cocaine into a
larger volume to have more to sell. Brown also inter-
preted several words as references to money: York’s
reference to “six” meant $6,000, which Brown said was
the cost of the drugs; “five dollar” meant $500; and “fifty-
five” meant $5,500.
  Brown wasn’t the only witness to interpret the drug
lingo in the recorded conversations. The government
called (and formally offered) Officer Robert Coleman as
an expert witness. Coleman had extensive experience in
No. 07-2032                                              7

narcotics investigations but he was not involved with
York’s investigation. He only reviewed the transcripts
of the recorded conversations so he could give his
opinion on their meaning. Most of Coleman’s transla-
tions of the code words were identical to Brown’s—the
words referred to drugs and drug paraphernalia. Plus,
Coleman testified to a few phrases that Brown did not,
such as York’s telling Mitchell, “get your money
straight,” which Coleman interpreted as York telling
Mitchell to “get his money together for the nine-ounce
purchase.” Coleman also testified to his knowledge of
narcotics transactions in the local area. He testified that
wholesale amounts of cocaine are sold in half, quarter, or
eighth of a kilogram quantities and that a quarter kilo-
gram (or nine ounces) of crack costs between $5,000
and $6,000 and can be as much as $9,000.
  The jury convicted York of delivering 50 grams or more
of cocaine base. The district court sentenced York to 360
months’ imprisonment and 10 years of supervised release.
  York appeals both his conviction and his sentence. York
seeks a new trial by arguing that the district court
should have excluded both Brown’s and Coleman’s
interpretation testimonies. We review each agent’s testi-
mony in turn. York seeks re-sentencing based on the
retroactive amendment to the crack cocaine guidelines.


                            II.
A. Agent Brown’s Interpretation Testimony
  York levels an array of attacks against Brown’s interpre-
tations of the drug jargon that laced York’s and Mitchell’s
8                                               No. 07-2032

recorded conversations. Through various interrelated
arguments, York contends that Brown’s interpretation
testimony was inadmissible under Federal Rules of Evi-
dence 702 and 403, Federal Rule of Criminal Procedure
16(1)(g), and the Sixth Amendment’s Confrontation
Clause. After untangling York’s claims, we find a portion
of Brown’s testimony problematic. The district court
should have excluded Brown’s interpretations of the
words “six,” “five dollar,” and fifty-five.” The rest of
Brown’s interpretations, however, was admissible.
  To begin, we must determine whether Brown’s inter-
pretations were admissible only as expert opinion testi-
mony under Fed. R. Evid. 702. The government
concedes that they were, and we agree. Opinions or
inferences based on “scientific, technical, or other special-
ized knowledge within the scope of Rule 702” are not
admissible as lay testimony under Fed. R. Evid. 701. Such
opinions or inferences, drawn from facts outside
the witness’s first-hand knowledge of the case, are ad-
missible only as expert testimony. United States v. Conn,
297 F.3d 548, 553-54 (7th Cir. 2002). Brown’s interpreta-
tion testimony fit the “expert” mold. Though Brown
had first-hand knowledge of York’s investigation, the
government asked Brown to rely on his experience in
prior crack cocaine investigations to explain the hidden
meaning of certain words in York’s and Mitchell’s con-
versations. See United States v. Oriedo, 498 F.3d 593, 603 &
n.10 (7th Cir. 2007). For the most part, Brown did not
claim that he learned the meaning of these words
during the course of his investigation of York. (We say
“for the most part” because on a few occasions it was
No. 07-2032                                                9

unclear what body of knowledge Brown relied on to
inform his interpretation of certain words, which as you
will later see, causes us some concern.) Cf. United States
v. Rollins, 544 F.3d 820, 833 (7th Cir. 2008) (finding
law enforcement witness’s interpretations of code words
as admissible lay testimony where witness based inter-
pretation only on listening first-hand to numerous re-
corded telephone calls in that particular investigation).
So by generally relying on his specialized knowledge,
Brown testified as an expert.
   Expert testimony has its benefits for the party who offers
it, but it also has its burdens. Rule 702 requires that an
expert be qualified “by knowledge, skill, experience,
training, or education” to render his opinion, and that
the opinion “assist the trier of fact to understand the
evidence or to determine a fact in issue.” Rule 702 also
requires that “(1) the testimony is based upon sufficient
facts or data, (2) the testimony is the product of reliable
principles and methods, and (3) the witness has applied
the principles and methods reliably to the facts of the
case.” In addition, prior to trial, the government must
disclose to the defendant a written summary of the
expert’s testimony, which “describe[s] the witness’s
opinions, the bases and reasons for those opinions, and the
witness’s qualifications.” Fed. R. Crim. P. 16(a)(1)(G).
Finally, if the witness testifies as both a fact witness and
an expert witness in the same trip to the witness stand
(like Brown did here), the government and the court
must take some special precautions to make clear for
the jury when the witness is relying on his expertise and
when he is relying only on his personal knowledge of
10                                             No. 07-2032

the case. See, e.g., United States v. Upton, 512 F.3d 394,
401 (7th Cir. 2008).


 1.   Qualifying Agent Brown as an “Expert”
  York argues that the government failed to fulfill a
number of these burdens when it asked Brown to opine
on the meaning of York’s and Mitchell’s conversations.
First, York contends that Brown’s interpretation testi-
mony should have been excluded because the district
court failed to formally “qualify” Brown as an expert
and did not permit York to conduct a voir dire re-
garding Brown’s qualifications. District courts have a
“gatekeeping” duty to ensure that witnesses do not offer
expert testimony before the court is satisfied that Rule
702’s requirements are met. See Kumho Tire Co., Ltd. v.
Carmichael, 526 U.S. 137, 147 (1999); United States v.
Moore, 521 F.3d 681, 684 (7th Cir. 2008); Conn, 297 F.3d at
555-56. However, “[a] judge is not obliged to look into
the questions posed by Rule 702 when neither side
either requests or assists.” Moore, 521 F.3d at 685. York’s
trial counsel failed to object to Brown’s qualifications or
any other aspect of Brown’s testimony until well after
Brown began defining words like “half” and “hard.” Only
near the end of Brown’s interpretation testimony did
York’s counsel object to Brown’s “basis of knowledge,” to
which the court responded that Brown’s “extensive
involvement in prior drug narcotics investigations” made
him “competent to testify to his understanding” of
York’s and Mitchell’s drug jargon.
No. 07-2032                                               11

   We are hard-pressed to say that York’s general founda-
tion objection preserved any challenge to Brown’s qualifi-
cations, the lack of voir dire, or whether Brown’s
testimony was based on “sufficient facts or data” and
“reliable principles and methods.” See Fed. R. Evid.
103(a)(1) (requiring a “timely objection . . . stating the
specific ground of objection, if the specific ground was not
apparent from the context” (emphasis added)); Rollins,
544 F.3d at 834. Even if it did, any error flowing from
the district court’s failure to formally anoint Brown an
expert was harmless. We have routinely held that “narcot-
ics code words are an appropriate subject for expert
testimony.” United States v. Farmer, 543 F.3d 363, 370
(7th Cir. 2008); see also United States v. Foster, 939 F.2d
445, 451 (7th Cir. 1991). A law enforcement officer’s
understanding of the drug trade, which comes from
that officer’s prior experience policing illicit narcotics
transactions, is “specialized knowledge” within Rule 702.
See Oriedo, 498 F.3d at 603 & n.10. So we allow officers
whose testimony is based on some aspect of that under-
standing (such as the meaning of drug code words),
rather than on first-hand knowledge of the particular
investigation in the case, to testify as experts. Id. at 603-
04; United States v. Hughes, 970 F.2d 227, 236 (7th Cir.
1992). Notably, York does not challenge Brown’s quali-
fications, his methods, or the accuracy of his testi-
mony here on appeal. Brown testified that he had served
17 years as an FBI agent and been involved in approxi-
mately 200 narcotics investigations prior to testifying.
Brown also testified that during his experience in drug
investigations he learned some of the language of the
12                                              No. 07-2032

drug trade and he relied on that knowledge to define
most of the drug lingo. Therefore, given Brown’s quali-
fications, and no attempt to disparage them here on
appeal, we find that Brown would have easily qualified
as an expert had the court conducted the formal Rule 702
analysis.
  Along these lines, we find that York suffered no preju-
dice by being unable to conduct a formal voir dire of
Brown before he testified. York was able to and did cross-
examine Brown on his qualifications and methods at
trial. On appeal, York gives us no reason to question
those qualifications or methods. So we won’t. See Oriedo,
498 F.3d at 604. (“Although Mr. Oriedo makes the blanket
assertion that he was deprived of an opportunity to
cross-examine adequately Agent Gourley or prepare a
defense, before this court he questions neither the
accuracy of the statements offered nor the qualifications
of Agent Gourley to make them.”).


  2.   Expert Disclosure Requirements
  Next, York hints that the government ignored the
expert disclosure requirements of Fed. R. Crim.
P. 16(a)(1)(G). Indeed, it appears the government did.
Since the government planned to elicit expert opinion
testimony from Brown, it should have provided a sum-
mary of Brown’s testimony to York’s counsel prior to
trial. See Oriedo, 498 F.3d at 604. But York never raised
this issue below, which limits our review to plain error.
United States v. Navarro, 90 F.3d 1245, 1259 (7th Cir. 1996).
On appeal, York does not identify any prejudice that he
No. 07-2032                                              13

suffered as a result of this non-disclosure, which would
justify outright exclusion of Brown’s testimony (or any
other sanction under Fed. R. Crim. P. 16(d)(2) for that
matter). See United States v. Duvall, 272 F.3d 825, 829 (7th
Cir. 2001). We don’t see how there could be any. Brown’s
testimony at York’s second trial mirrored his testimony
from the first. At the first trial, Brown explained
his extensive experience with narcotics investigations
and then relied on that expertise to interpret many of
the same code words he defined at the second trial.
Moreover, York’s lawyer was the same for both trials. So
defense counsel could not claim that he suffered some
unfair surprise and was caught unaware of Brown’s
qualifications and opinions, and the bases and reasons
for those opinions, going into the second trial. This
is not to say that every time a defendant is retried the
government need not disclose the experts from the
prior trial whom the government intends to call again.
But here, where Brown’s testimony was nearly identical
in both trials, and where York does not allege any dis-
advantage in preparing for the second trial or cross-
examining Brown, we cannot see any prejudice that
would justify exclusion nor any plain error that would
justify reversal.


  3.   Helpfulness of Agent Brown’s Testimony
  York next argues that Brown interpreted some words
and sounds that were not drug code and therefore needed
no interpretation. Specifically, York challenges Brown’s
interpretation of the numbers “six,” “nine,” “five dollar,”
14                                              No. 07-2032

and “fifty-five,” as well as Brown’s comment that he
heard the sound of money being counted over the audio
transmitter. This testimony, according to York, exceeded
the proper scope of expert testimony under Rule 702. We
see two different claims growing out of this single chal-
lenge. First, York contends that, by interpreting words
already within the jury’s understanding, Brown’s testi-
mony did not meet Rule 702’s requirement that expert
testimony “assist” the jury. Second, because these words
and sounds were not “code,” in York’s view, Brown’s
testimony was not based on sufficient facts and reliable
methods as Rule 702 requires. Because York’s trial objec-
tion arguably encompasses these claims, we review them
for an abuse of discretion. Farmer, 543 F.3d at 370.
  Turning to that first claim, we have discussed that
the Rules of Evidence allow expert law enforcement
witnesses to translate drug jargon and code words
that might seem entirely innocuous to an untrained jury.
United States v. Ceballos, 302 F.3d 679, 687-88 (7th Cir.
2002); Foster, 939 F.2d at 451-52 (“Despite our country’s
‘war on drugs’ and its accompanying media coverage, it
is still a reasonable assumption that jurors are not
well versed in the behavior of drug dealers.”). But this
presupposes that the terms to be interpreted are in fact
drug code and not words “that the jury can evaluate
for itself.” United States v. de Soto, 885 F.2d 354, 361 (7th
Cir. 1989). “Interpretations” of unambiguous words
or phrases that are plainly within the jury’s under-
standing are unlikely to be admissible under Rule 702;
they would not “assist the trier of fact to understand
the evidence or to determine a fact in issue.” See United
States v. Rollins, 862 F.2d 1282, 1292 (7th Cir. 1988).
No. 07-2032                                                 15

Instead, they would merely put an expert gloss on a
conclusion the jury should draw.
  In Ceballos, 302 F.3d at 687-88, we upheld agents’ inter-
pretations of simple pronouns such as “it,” “them,” and
“both” as referring to methamphetamine shipments,
in part, because defendants used those pronouns am-
biguously in their conversation (they mentioned no
other nouns to which the pronouns could refer).
Given this ambiguity, we concluded that the agents’
experience interpreting drug code language would be
helpful to the jury. Id. at 688; see also Rollins, 862 F.2d
at 1292 (upholding agent’s interpretation of “t-shirts,”
“stuff,” and “it” as code words referring to cocaine).
  Here, the terms “six,” “nine,” “five dollar,” and “fifty-
five” were facially ambiguous. York told Mitchell, “That
shit costs . . . six . . . “, and then later said, “That’s nine
right, that’s nine like that, you wait on it.” The question is,
six and nine of what? Though York’s reference to “cost”
gives the jury some indication that “six” refers to pay-
ment, the term “six” was still sufficiently ambiguous
(does it mean money or something else and how
much?). The references to “five dollar” and “fifty-five”
were equally unclear. Given our decisions in Ceballos
and Rollins, we have no qualms concluding that
Brown’s interpretation of these vague terms would
assist the jury.


  4.   Foundation for Agent Brown’s Interpretations
  But that alone doesn’t mean Brown’s testimony was
admissible—Rule 702 requires more than a qualified
16                                                No. 07-2032

expert and helpful testimony. Brown must have had a
reliable basis for opining that words like “six” and “fifty-
five” are in fact drug lingo. Fed. R. Evid. 702; see also
Conn, 297 F.3d at 555 (“The second prong of the test set
forth in Rule 702 requires that the testimony be the
product of reliable principles and methods.”). York
argues that Brown had no basis for such an opinion
because these numbers do not refer to anything. To illus-
trate, York contrasts his case to United States v. Moon,
512 F.3d 359, 363 (7th Cir. 2008), where we upheld an
agent’s interpretation of “four, five, or six meals” as
referring to between four and six kilograms of cocaine.
Though the agent interpreted the numbers as quantities
of drugs, the code word in Moon was the word “meals.”
York’s case is different, he argues, because the numbers
in his and Mitchell’s conversations lacked any reference
to another noun that could serve as the coded term.
  York supports his view with the Second Circuit’s
opinion in United States v. Dukagjini, 326 F.3d 45, 55 (2d Cir.
2003). In Dukagjini, a law enforcement expert witness
interpreted the words “six” and “ten” in the expressions,
“tell ‘em to bring . . . the six or whatever,” and “tell him
to come with the ten,” to refer to quantities of heroin.
Id. (emphasis added). The Second Circuit found that
admitting this testimony was erroneous because the
words “six” and “ten,” though ambiguous, were not
drug code: “There was no evidence that these phrases
were drug code with fixed meaning either within the
narcotics world or within this particular conspiracy.” Id.
Drawing on Dukagjini, York argues that words like “six”
and “fifty-five” do not have “fixed meanings” and there-
No. 07-2032                                              17

fore should not be treated as drug code that an expert
can interpret.
  We find York’s view too narrow. Experts need not
establish that certain words have fixed meanings only in
the narcotics world or in the particular conspiracy
before they can interpret those words. Experts can deter-
mine, based on their expertise, that certain words have
drug-related meanings within the context of a single
conversation. In Ceballos, for example, agents inter-
preted the words “it,” “them,” and “both” as referring
to shipments of methamphetamine. 302 F.3d at 687.
Those words certainly lack any “fixed meaning” in the
narcotics world or elsewhere—“it” does not always
mean meth. But in the context of that conversation, where
the pronoun “it” had no antecedent, the agents,
drawing on their expertise, had a reliable basis to
conclude that those words referred to drugs. Id. at 687-88.
  The same is true here. Mitchell’s and York’s conversa-
tions were laced with words that Brown testified were
common drug parlance (and did have fixed meanings
in the drug trade)—i.e., “soft” meant powder cocaine,
“hard” meant crack cocaine, and “cook” meant
processing powder into crack. Brown knew Mitchell
and York were talking about drugs. So when Mitchell
asked for “nine, nine probably hard,” the word “nine” was
not just dangling in the conversation, unlinked to any
drug code word, as York suggests. “Nine” and “hard”
went together, just like “four, five, and six” went together
with “meals” in Moon, 512 F.3d at 363. So Brown had
a reliable basis to opine that York and Mitchell were
18                                              No. 07-2032

negotiating a crack deal (York also told Mitchell what
the “shit costs”), and Brown’s experience in narcotics
transactions could inform his opinion about common
quantities and prices for the drugs. Between his
expertise and the context of the conversation, Brown
could interpret “nine” as the agreed-upon quantity
and “six,” “five dollar,” and “fifty-five” as efforts to
negotiate the price.
   Brown also had a sufficient basis, though not an expert
basis, to testify that he heard the sound of money being
counted on the audio transmitter. A witness’s testimony
about the sounds he heard is one of the “ ‘prototypical
example[s] of the type of evidence contemplated by the
adoption of Rule 701.’ ” Fed. R. Evid. 701 advisory com-
mittee’s note (insertion in original) (quoting Asplundh Mfg.
Div. v. Benton Harbor Eng’g, 57 F.3d 1190, 1196 (3d Cir.
1995)); see also Conn, 297 F.3d at 554 (“Lay opinion testi-
mony most often takes the form of a summary of
first-hand sensory observations.”). So this part of Brown’s
testimony was admissible as lay opinion testimony.


  5.   Dual Testimony
  But did Brown actually rely on his expertise when he
interpreted the code words? Or did he rely on some
other basis, such as a conversation with the non-
testifying Mitchell, which might pose problems under
the Rules of Evidence and the Sixth Amendment? That’s
the crux of York’s final two challenges to Brown’s testi-
mony—the dual nature of Brown’s testimony and the
Confrontation Clause concerns that such dual testimony
No. 07-2032                                                19

raises. Because Brown’s general “basis of knowledge”
objection did not preserve these two claims, we review
them only for plain error. United States v. Pree, 408 F.3d
855, 868-69 (7th Cir. 2005).
  York argues that Brown impermissibly testified as
both an expert and a fact witness in the same trip to
the witness stand. Though such a practice is routinely
upheld, particularly where experienced law enforcement
officers were involved in the particular investigation at
issue, e.g., United States v. Mansoori, 304 F.3d 635, 654 (7th
Cir. 2002), there are some inherent dangers with this
kind of dual testimony, see Upton, 512 F.3d at 401; de Soto,
885 F.2d at 360; Dukagjini, 326 F.3d at 53-54. For example,
the witness’s dual role might confuse the jury. United
States v. Goodwin, 496 F.3d 636, 641 (7th Cir. 2007); Fed. R.
Evid. 403. Or, the jury might be smitten by an expert’s
“aura of special reliability” and therefore give his
factual testimony undue weight. United States v. Brown,
7 F.3d 648, 655 (7th Cir. 1993). Or, “the jury may unduly
credit the opinion testimony of an investigating officer
based on a perception that the expert was privy to facts
about the defendant not presented at trial.” Upton, 512
F.3d at 401.
   Given these dangers, district courts must take some
precautions to ensure the jury understands its function
in evaluating this evidence. Id. The jury needs to know
when an agent is testifying as an expert and when he
is testifying as a fact witness. “The potential for prejudice
in this circumstance can be addressed by means of appro-
priate cautionary instructions and by examination of the
20                                               No. 07-2032

witness that is structured in such a way as to make clear
when the witness is testifying to facts and when he is
offering his opinion as an expert.” Mansoori, 304 F.3d at
654. We have recognized other precautions as well, such
as the government’s establishing the proper foundation
for the witness’s expert opinions, Farmer, 543 F.3d at 370-
71, and the district court allowing the defense to
rigorously cross-examine the expert about his interpreta-
tion of the drug lingo, id. at 371; United States v. Parra,
402 F.3d 752, 759-60 (7th Cir. 2005).
  The protective steps taken in this case were not the
model of how to handle a witness who testifies in a dual
capacity. We recognize that the government established
an adequate foundation for Brown’s testimony, as we
have discussed, outlining his years of expertise with
drug investigations. And we certainly credit the fact that
the court put no limits on York’s opportunity to cross-
examine Brown; York’s counsel took full advantage of
that opportunity to delve into both Brown’s qualifica-
tions and his interpretations of certain words in the
recorded conversations. Counsel repeatedly questioned
Brown’s basis for his understanding of the words, high-
lighting the fact that neither Mitchell nor York ever specifi-
cally mentioned cocaine or crack in their conversations.
These measures went part of the way toward minimizing
the dangers of dual testimony.
  But the court and the government were less vigilant
in instructing the jury and structuring Brown’s testi-
mony. For instance, though the court did instruct the jury
on how it should evaluate opinion testimony from wit-
No. 07-2032                                            21

nesses with special knowledge or skill, this instruction
came at the end of the trial. It would have been far
more effective for the court to have explained Brown’s
dual role to the jury before Brown testified and then
flag for the jury when Brown testified as a fact witness
and when he testified as an expert. See Upton, 512 F.3d at
401 (“Before [Detective] Eversman’s testimony, the
district court gave a cautionary instruction explaining
that Eversman would be serving both functions as a
witness.” (emphasis added)).
  What gives us the greatest cause for concern, though, is
the structure of Brown’s testimony. The government
started off well. It appropriately signaled to the jury
that Brown was relying on his expertise and not his
knowledge of York’s investigation when it asked Brown
whether, during his involvement in over 200 investiga-
tions, he learned some terms of the drug trade. In its
follow-up questions, the government took a similar tack,
prefacing its questions with phrases like, “based on your
experience in crack cocaine investigations . . . .” This
structure helped minimize jury confusion. See Farmer,
543 F.3d at 371 (approving questions with similar intro-
ductory remarks).
  But then things got murky. The government switched
back to questioning Brown about the investigation, which
of itself might not have been problematic, had the gov-
ernment not decided, several moments into Brown’s
factual testimony, to go back and question Brown about a
few more code words—“six,” “fifty-five,” and “five
dollar.” Seamlessly switching back-and-forth between
22                                                No. 07-2032

expert and fact testimony does little to stem the risks
associated with dual-role witnesses. Even more problem-
atic was the way in which the government prefaced
these questions: “Based on your experience of [sic]
crack cocaine investigations and this investigation in particu-
lar . . . .” (emphasis added). This phrasing explicitly mixed
Brown’s dual bases of knowledge, leaving the jury to
wonder who was testifying, Brown-the-expert or Brown-
the-case-agent. Given this heightened possibility for
juror confusion, coupled with the lack of a timely cau-
tionary instruction and the fact that we cannot discern
whether Brown’s interpretations were actually based on
his expertise or a conversation with Mitchell, we
conclude that the court erred in admitting Brown’s re-
sponses to the government’s questions about “six,” “fifty-
five,” and “five dollar.” (We will address whether those
were plain errors momentarily.) Other than these three
interpretations, though, Brown’s testimony did not
offend Rules 403 and 702 to such an extent that we can
say the district court erred in admitting it.


  6.   Confrontation
  Lastly, York argues that Brown’s interpretation testi-
mony violated his Sixth Amendment right “to be con-
fronted with the witnesses against him.” York’s argument
grows out of Crawford v. Washington, in which the
Supreme Court held that the Sixth Amendment’s Con-
frontation Clause prohibits admitting testimonial
hearsay evidence unless the declarant is unavailable and
the defendant had a prior opportunity to cross-examine
No. 07-2032                                                  23

him. 541 U.S. 36, 68 (2004); see also United States v. Tolliver,
454 F.3d 660, 664-65 (7th Cir. 2006). Our focus here is on
the fact that Crawford applies only to hearsay, which
must be a statement offered for the truth of the matter
asserted. Crawford, 541 U.S. at 59 n.9 (“[The Confrontation
Clause] does not bar the use of testimonial statements
for purposes other than establishing the truth of the
matter asserted.”); see Fed. R. Evid. 801(c). We are no
stranger to Crawford-based Confrontation Clause chal-
lenges to the admission of previously recorded conversa-
tions between informants and defendants. E.g., United
States v. Van Sach, 458 F.3d 694, 700-02 (7th Cir. 2006);
Tolliver, 454 F.3d at 666. We have held that playing the
tapes of those conversations for the jury does not
violate the Confrontation Clause so long as those tapes
are offered to provide context for the defendant’s own
admissions. United States v. Nettles, 476 F.3d 508, 517-18
(7th Cir. 2007); Van Sach, 458 F.3d at 701; Tolliver, 454
F.3d at 666. When offered for context and not for the
truth, the declarant’s statements are not hearsay,
United States v. Gajo, 290 F.3d 922, 930 (7th Cir. 2002);
United States v. Davis, 890 F.2d 1373, 1380 (7th Cir. 1989),
and thus not subject to Crawford.
  In this case, the government offered Mitchell’s recorded
statements to help the jury to understand York’s state-
ments during his dealings with Mitchell. Mitchell’s state-
ments were not offered for their truth—i.e., it was irrele-
vant whether Mitchell actually desired nine ounces of
cocaine or intended to “boost up” the drugs. Mitchell’s
statements were offered to show how York reacted to
them. For example, after Mitchell said, “Just bring me
24                                               No. 07-2032

nine,” York responded, “You want me to cook it?” Mitch-
ell’s statement allowed the jury to understand that York
was not offering to fix supper. In other words, Mitchell’s
statements put York’s reactions into “context” and
hence were not hearsay. Moreover, we see no indication
that Mitchell tried to “put words into [York’s] mouth or . . .
persuade [York] to commit more crimes in addition
to those that [York] had already decided to commit.”
Nettles, 476 F.3d at 518. So admitting Mitchell’s state-
ments, by itself, did not offend York’s confrontation rights.
  York concedes as much here on appeal. But York con-
tends that Brown’s interpretations of Mitchell’s state-
ments make this case different. In essence, York argues
that Brown’s interpretations transformed Mitchell’s
recorded statements from merely providing context to
being offered for their truth.
  But interpreting an informant’s statements would not
alter the government’s use of those statements. Brown
translated Mitchell’s code words into terms that jurors
could understand. If Mitchell had not used code and
instead said plainly to York, “I need nine ounces of crack
cocaine,” that statement would still be admissible as
context for York’s responses. Whether Mitchell spoke to
York in drug lingo or plain English would not affect
the purpose for which those statements were used.
Because Mitchell’s out-of-court statements, translated or
untranslated, were offered as context for York’s side of
these inculpatory discussions, they do not implicate the
Confrontation Clause.
  We might have a confrontation problem, however, if
Brown based his interpretations on his own conversa-
No. 07-2032                                               25

tions with Mitchell and not on his knowledge of the drug
trade and review of the transcripts. See United States v.
Silva, 380 F.3d 1018, 1020 (7th Cir. 2004); United States v.
Mejia, 545 F.3d 179, 198-99 (2d Cir. 2008). For instance, if
Mitchell told Brown that “hard” meant crack and Brown
relied on that information when he interpreted the word
“hard” at trial, Mitchell’s statements to Brown (as
opposed to Mitchell’s conversations with York) would
have been offered for their truth. No matter that
Mitchell’s recorded conversations were offered for
context, Mitchell’s statements to the agents would have
been hearsay and the agents’ reliance upon them might
implicate Crawford.
  But we see little or no evidence of that here. Brown
did speak to Mitchell during the investigation: he “de-
briefed” Mitchell after both encounters with York. Brown
testified that, after the first encounter, he told Mitchell
to “go back and wait for Mr. York to deliver the quantity
of drugs that he just ordered.” York argues that
Brown’s knowledge of Mitchell’s “order,” including the
details of that order (e.g., the thing ordered, quantity, and
cost), could only have come from a conversation with
Mitchell. Not so. As we have discussed, Brown had a
working knowledge of the meanings of drug jargon
and code words. Brown listened to Mitchell’s and
York’s conversations in real time and, by the time he
debriefed Mitchell, was well aware that they were negoti-
ating a drug transaction. Moreover, before testifying at
trial, Brown reviewed the transcripts of the recordings
and testified about the meaning of certain words based
on his experience. We have no indication that those
26                                              No. 07-2032

interpretations were based on conversations with Mitch-
ell. All we have is a mere possibility of an impermissible
basis for three of those interpretations—“six,” “fifty-five,”
and “five dollar”—which Brown defined relying on both
his expertise and involvement in York’s investigation.
Because we have already excluded those interpretations
as improperly safeguarded dual testimony, however,
we need not decide whether their admission also violated
Crawford.
                           * * *
  In sum, we find that most of Brown’s interpretation
testimony was admissible. However, given the lack of
precautions taken to minimize the dangers of dual testi-
mony, Brown’s interpretations of “six,” “fifty-five,” and
“five dollar” as referring to certain dollar amounts
should have been excluded.


B. Officer Coleman’s Interpretation Testimony
  York also challenges Coleman’s testimony. Like Brown,
Coleman interpreted the drug jargon and code words in
York’s and Mitchell’s conversations. Unlike Brown,
Coleman was formally qualified as an expert and had no
experience with York’s investigation beyond reviewing
the audio recording transcripts. Still, York argues that
the district court should have excluded Coleman’s testi-
mony for two of the same reasons that he believes
Brown’s testimony was inadmissible.
  First, York contends that Coleman’s testimony violated
the Confrontation Clause. But we know from our
No. 07-2032                                            27

previous discussion of this issue that York’s argument
here must fail. Simply because Coleman interpreted
Mitchell’s words based on his expertise did not change
the government’s use for playing the audio tapes—to
provide context for York’s admissions. Using the tapes
and Coleman’s interpretation of them did not implicate
Crawford. Moreover, Coleman was not involved in the
investigation and never spoke with Mitchell. Coleman
interpreted Mitchell’s statements based solely on his
expertise; York does not contend otherwise. So
Coleman’s testimony did not draw on any hearsay
from Mitchell and therefore did not infringe York’s con-
frontation rights.
  Second, York argues that Coleman interpreted words
that needed no interpretation, thereby exceeding the
proper scope of expert testimony. York challenges all of
Coleman’s interpretation testimony and specifically
targets Coleman’s translation of numbers like “six” and
“nine” as well as his interpretation of the phrase “get
your money straight” (a phrase on which Brown did not
comment). We review for an abuse of discretion.
Farmer, 543 F.3d at 370.
  As we have discussed, York’s and Mitchell’s vague or
coded references to drugs and money were ambiguous
and not readily understood by lay jurors. So Coleman’s
interpretations of words like “hard,” “soft,” “six,” and
“nine” assisted the jury in understanding those words.
Fed. R. Evid. 702; see Ceballos, 302 F.3d at 688. In addi-
tion, Coleman’s expertise gave him a reliable basis to
opine on the meanings of those words. Coleman did not
28                                             No. 07-2032

rely on his personal knowledge of the investigation—he
didn’t have any beyond the transcripts. Instead, Coleman
testified that, in his experience, nine ounces of cocaine
(equal to a quarter kilogram) was a wholesale quantity
and that the price of that quantity was “anywhere
between five or $6,000 up to maybe 9,000.” Coleman’s
knowledge of common quantities and prices gave him
a reliable basis to interpret the otherwise undefined
terms “six” and “nine” as $6,000 and nine ounces of
cocaine. Therefore those interpretations were admissible.
   This reasoning also extends to Coleman’s interpretation
of “get your money straight.” York contends that
Coleman’s testimony was unhelpful because this
phrase had no other reasonable interpretation than the
one Coleman gave it: “York is telling Mitchell to get his
money together for the nine-ounce purchase.” We dis-
agree. The phrase might have meant a variety of
things, such as “get your money from a clean source,” or
it might have referred to a desire for bills of certain de-
nominations, or York might have been telling Mitchell
to physically straighten up the cash he brought with
him. In other words, we think the phrase “get your
money straight” was just another form of drug slang
and, without Coleman’s interpretation, would have
remained ambiguous to jurors. The court did not err
in admitting that interpretation.


C. Harmless Error
  To review where we are at this point, we think that the
district court should have excluded Brown’s interpreta-
No. 07-2032                                               29

tions of “six,” “fifty-five,” and “five dollar” as improper
dual testimony. But that doesn’t mean we must reverse.
Under either a plain error standard or an abuse-of-discre-
tion standard, if those errors were harmless, York’s con-
viction will stand. United States v. Ortiz, 474 F.3d 976, 982
(7th Cir. 2007). Harmlessness means that the jury would
have convicted even absent the errors. Id.; see also United
States v. Owens, 424 F.3d 649, 656 (7th Cir. 2005) (“The
test for harmless error is whether, in the mind of the
average juror, the prosecution’s case would have been
‘significantly less persuasive’ had the improper
evidence been excluded.”).
   We are convinced that failing to exclude these three
interpretations was harmless; the evidence against York
was overwhelming. The jury knew that after Mitchell’s
first meeting with York, Mitchell had $6,000 less than
when he started. And after their second meeting, Mitchell
had nine ounces of crack cocaine on him. The admissible
portions of Brown’s testimony and all of Coleman’s
bolstered the inference that Mitchell and York negotiated
and executed a drug deal and diminished any possibility
that Mitchell received the drugs from anywhere else,
such as from his wife. Their interpretations of “half,”
“nine,” “hard,” “soft,” “work,” “cook,” “sellable,” and
“boost up” made York’s intentions clear. Even without
Brown’s interpretation of certain numbers, Coleman
told the jury that York and Mitchell were discussing
prices, that $6,000 was within the range of going rates
for cocaine, and that in his experience “six” meant $6,000.
We think it impossible that Brown’s testimony reinforced
Coleman’s in such a way that the exclusion of a small
30                                              No. 07-2032

portion of Brown’s testimony would have caused the
jury to reach a different verdict. Because any error
below was harmless beyond a reasonable doubt, we
AFFIRM York’s conviction.



                            III.
  York wants to petition the district court to reduce his
sentence in light of the retroactive application of the
revised crack guidelines. See Supplement to the 2007
United States Sentencing Guidelines Manual at 1-4
(Mar. 3, 2008) (U.S.S.G. § 1B1.10(c)); United States Sentenc-
ing Commission Guidelines Manual, Supplement to
Appendix C, 226-31 (2008) (Amendment 706). So he asks us
to remand his sentence. But remand is not required to
pursue that avenue of relief. United States v. Tatum, 548
F.3d 584, 588 (7th Cir. 2008). Instead, York should file a
motion in the district court pursuant to 18 U.S.C.
§ 3582(c)(2). Id.


                            IV.
  In light of the foregoing, we AFFIRM the judgment of the
district court.




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