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

No. 04-2406
UNITED STATES OF AMERICA,
                                                 Plaintiff-Appellee,

                                 v.

FEMI JOHNSON,
                                            Defendant-Appellant.
                          ____________
            Appeal from the United States District Court
       for the Northern District of Illinois, Eastern Division.
          No. 01 CR 103—Matthew F. Kennelly, Judge.
                          ____________

 ARGUED DECEMBER 2, 2005—DECIDED FEBRUARY 10, 2006
                   ____________



  Before BAUER, POSNER, and MANION, Circuit Judges.
  BAUER, Circuit Judge. A jury convicted Femi Johnson of
one count of conspiring to possess with intent to distribute,
and to distribute, heroin in violation of 21 U.S.C. § 846, and
two counts of possession of heroin with intent to distribute
in violation of 21 U.S.C. § 841(a)(1). Johnson challenges his
conviction claiming prosecutorial misconduct, insufficient
evidence to support the jury verdict, failure of the district
court to instruct the jury properly, and denial of his right to
present witnesses in his defense. He also challenges his
sentence. We affirm Johnson’s conviction but order a
limited remand to the district court in accordance with our
2                                               No. 04-2406

decision in United States v. Paladino, 401 F.3d 471 (7th Cir.
2005).


                     I. Background
  In November 1999, a government informant named Henry
Adebayo engaged Kenny Mohammed, whom he knew to be
a drug dealer, in a series of recorded conversations to
arrange heroin purchases. Mohammed told Adebayo that he
had to call a friend, Johnson, to obtain heroin. Mohammed
and Johnson agreed that a sale would take place when
Mohammed informed Johnson that the buyer was ready.
  On January 28, 2000, agents fitted Adebayo with a
recording device and supplied him with buy money. While
waiting with Adebayo at Leona’s restaurant in Hyde Park,
Mohammed received a phone call and told the caller that he
would meet him shortly. When they left Leona’s, Adebayo
returned to his car; Mohammed entered a wine-colored
Toyota Corolla, driven by a black male, with tinted windows
and Texas license plates. Agents then observed Mohammed
walk to Adebayo’s car, take the buy money, return to and
enter the Corolla, exit and walk back to Adebayo’s car, and
hand Adebayo an object resembling a newspaper. This
comports with Adebayo’s later testimony that he and
Mohammed exchanged the buy money for heroin while the
two men were in Adebayo’s car in front of the nearby
McDonald’s. Mohammed, on the other hand, later testified
that Adebayo gave him the money while they were still at
Leona’s, and that he gave Adebayo the heroin while they
stood in front of the McDonald’s. After Mohammed left the
car, agents saw Adebayo drive off, followed him, and
recovered fifty grams of heroin from inside the newspaper.
Another agent followed the Corolla to the north side of the
city, where it turned around and headed south.
 After several more conversations with Mohammed,
Adebayo succeeded in scheduling another transaction for
February 16, 2000. Mohammed testified that he contacted
No. 04-2406                                                3

Johnson to tell him that his “guy” was ready and to order
seventy grams of heroin. When Johnson agreed and asked
where to meet, Mohammed instructed him to go to the
apartment building at 7337 S. South Shore Drive. Moham-
med testified that they agreed to the same unit price as was
paid for the January 28 transaction: “Since the other one
was $5,000, this one was $7,000, I told him already.” Later,
Mohammed received a phone call and traveled
with Adebayo to the apartment building, where they waited
for Johnson to arrive with the heroin.
  Agents monitored the apartment building in anticipation
of the second controlled purchase. Earlier, they had given
Adebayo $7,000 in buy money and recorded the serial
numbers on the bills. The same wine-colored Corolla arrived
at the apartment building. An agent observed Mohammed
make an exchange with the driver. Mohammed testified
that he took the heroin from Johnson in the Corolla,
brought it to Adebayo, exchanged it for the money, and then
went upstairs with Johnson to Mohammed’s apartment.
According to the agents, the fire lane in which the Corolla
was parked presented surveillance problems. As a result,
the agents did not observe Mohammed or Johnson enter the
building. Only by moving to an area just north of the fire
lane could DEA Agent William Wilson observe the Corolla
leave the apartment building.
  After the Corolla left, agents recovered the approximately
seventy grams of heroin from Adebayo, while Customs
Agent John Coleman followed the Corolla to the 8600 block
of South Saginaw Street. There, Coleman saw the driver
leave the car and enter a house, before returning to the car.
Agent Coleman again followed the Corolla, which proceeded
to turn right while signaling left, make a sharp right turn,
accelerate sharply, run two red lights, weave through
traffic, and run yield signs at cross streets. When Coleman
could no longer keep pace with the car, he radioed for
assistance. Officer Robert Sapp, who was part of the
4                                               No. 04-2406

surveillance team, pulled the Corolla over after it ran a
third red light. Johnson was the driver.
  Officer Sapp discovered $5,950 in U.S. currency wrapped
in newspaper in the glove compartment. Agents photocopied
the bills, whose serial numbers matched the ones agents
had recorded for $5,950 of the $7,000 given to Adebayo.
Agents gave Johnson a receipt for the money. On February
24, 2000, in order to maintain the covert nature of the
investigation, agents gave the money to Witness A, who
claimed that she had given it to Johnson to purchase a car
on her behalf. In early February 2001, Witness A was
indicted and arrested for making false statements to federal
agents in violation of 18 U.S.C. § 1001. While in custody,
she said that Johnson had paid her $200 to tell the agents
that the money belonged to her. Based on this statement,
the complaint was dismissed without prejudice, as the
government “expected her to be a cooperating witness.”
  On June 2, 2001, authorities arrested Johnson on conspir-
acy and possession charges. Shortly before trial, Witness A’s
attorney informed the government that she had reversed
herself again and was prepared to testify consistent with
her original statement. As a result, the government com-
plied with a court order requiring disclosure of impeach-
ment evidence by sending a letter to defense counsel
indicating that Witness A was again a possible subject of
investigation. In response to the defendant’s subpoena,
Witness A invoked her Fifth Amendment privilege against
self-incrimination.
  Johnson’s trial began on November 19, 2003. In both voir
dire questioning and opening statement, defense counsel
indicated that Johnson’s defense would be to attack Moham-
med’s credibility. During trial, the government called a
number of witnesses, including Agent Coleman, who gave
expert testimony that the supplier in a brokered drug deal
will often be present in the area to ensure that he receives
No. 04-2406                                                     5

payment from the sale proceeds, just as Johnson did on
these two occasions. Mohammed also testified for the
government, relating the circumstances of the two transac-
tions. The court allowed the government to introduce the
court’s order granting Mohammed immunity and compel-
ling his testimony. Accordingly, the prosecutor questioned
him on direct examination about his understanding of the
immunity agreement. On cross-examination, defense
counsel questioned Mohammed about the dependence of his
“safety valve ” reduction1 on pleasing the government with
his testimony against Johnson. On redirect, then, the
government questioned Mohammed about the facts omitted
by defense counsel, such as all five of the factors considered
by the court in determining safety valve eligibility.
  At trial, Johnson never set forth a buyer-seller defense;
rather, he argued that he was “not a drug dealer.” During
closing arguments, the prosecutor portrayed Mohammed as
a credible witness based on the evidence corroborating his
testimony. He stated that Mohammed “is here under an
order” and “understands he needs to tell the truth.” Defense
counsel, in closing argument, argued that “Kenny Moham-
med wasn’t telling the truth. He had every incentive to lie.”
Responding in rebuttal, the prosecutor again raised Moham-
med’s immunity agreement to demonstrate his incentive to
testify truthfully. No buyer-seller jury instruction was
requested by either party and none was given. On Novem-


1
   The safety valve provision of 18 U.S.C. § 3553(f) allows the
district court to depart below the statutory mandatory minimum
sentence for certain drug offenses if the defendant satisfies each
of the five criteria set forth in the statute. See also U.S.S.G.
§ 5C1.2. The provision generally applies “where the defendant is
a first time offender who was not the organizer or leader of
criminal activity and has made a good faith effort to cooperate
with the government.” United States v. Harrison, 431 F.3d 1007,
1013 (7th Cir. 2005).
6                                                No. 04-2406

ber 25, 2003, the jury found Johnson guilty of the conspir-
acy and possession counts. On May 14, 2004, Judge
Kennelly imposed an enhancement for obstruction of justice
under the Sentencing Guidelines and sentenced Johnson to
seventy months in prison. Johnson now challenges his
conviction and sentence.


                      II. Discussion
  Johnson advances the following five arguments on appeal:
(1) that prosecutors denied him a fair trial by improperly
vouching for the truthfulness of government witness
Mohammed during their case-in-chief and closing argu-
ment; (2) that the evidence presented by the government
was not sufficient to prove Johnson guilty of conspiracy and
possession beyond a reasonable doubt; (3) that the district
court erred when it failed to instruct the jury on a buyer-
seller defense; (4) that the government denied him the right
to present witnesses in his defense by threatening Witness
A with investigation and indictment; and (5) that the
district court violated Johnson’s Sixth Amendment rights by
enhancing his sentence for obstruction of justice. We
consider each claim in turn.


A. Fair Trial
  Johnson first contends that the government made im-
proper remarks during examination and closing argument,
thereby denying him a fair trial. Because Johnson did not
object at trial to the remarks he now challenges, we review
only for plain error. United States v. Renteria, 106 F.3d 765,
766 (7th Cir. 1997). Under the plain error standard, the
defendant must establish not only that the prosecutor’s
remarks were improper and denied him a fair trial, but also
that they prejudiced him by altering the outcome of the
No. 04-2406                                               7

proceedings. United States v. Sandoval-Gomez, 295 F.3d
757, 762 (7th Cir. 2002).


  1. Testimony Concerning Mohammed’s Immunity
     Agreement
  During direct examination of Mohammed, the district
court allowed the government to introduce the court’s order
granting Mohammed immunity and compelling his testi-
mony. The court specifically stated that introduction of the
order was warranted to show that Mohammed’s testimony
“can be used against him in a prosecution for perjury or
false statement.” Johnson now claims that the government
exceeded the bounds of the order and “told the jury” that
Johnson would be sent to jail if he testified falsely. The
prosecutor told the jury no such thing; instead, he merely
questioned Mohammed about his understanding of the
agreement:
    Q. So what could happen if you were to not tell the
    truth today?
    A. I will be sent to jail.
  This question was not improper—it was within the
bounds of the court’s order. Moreover, the government
immediately sought to clarify Mohammed’s comment about
being “sent to jail”:
    Q. Could you at least be prosecuted is what your un-
    derstanding is?
    A. Right.
    Q. Based on what you say here today?
    A. What did you say?
    Q. You could be prosecuted based on what you say here
    today if you were to not tell the truth; is that your
    understanding?
8                                               No. 04-2406

    A. Right, right, right.
This exchange does not, as Johnson claims, constitute
improper bolstering of a government witness. On direct
examination, the government may elicit testimony regard-
ing the witness’s guilty plea or immunity deal because
doing so allows the jury to hear “all relevant aspects of a
witness’s testimony at one time.” United States v. Montani,
204 F.3d 761, 766 (7th Cir. 2000). The government may
generally introduce this evidence regardless of whether the
witness’s credibility has already been attacked. Id. Here,
however, the government introduced this evidence on direct
examination because defense counsel had already signaled,
in voir dire questioning and in opening statement, that
Johnson’s defense would be to attack Mohammed’s credibil-
ity.
  The prosecutor in this case did not, as Johnson claims,
suggest that the government’s or the court’s authority
rested behind the witness’s testimony. Johnson cites to
several cases where other Courts of Appeals have found
that the government improperly vouched for the witness,
but each is readily distinguishable from the present case.
This is not a case where the prosecutor stated outright in
closing argument that the witness could not say “whatever
he wanted to say” because he would be prosecuted for
perjury, and that “the court wouldn’t allow” the government
to do anything wrong in the trial. See United States v.
Smith, 962 F.2d 923, 934 (9th Cir. 1992). Nor is it the case
where a prosecutor, again in closing argument, stated that
the witnesses would be in jeopardy if the government or the
court did not believe that they were telling the truth. See
United States v. Carroll, 26 F.3d 1380, 1389 (6th Cir. 1994).
Instead, here the government properly questioned Moham-
med about his understanding of the agreement he signed
with the government. As this Court has stated, “it is not
improper for the prosecutor to remind the jury of the
deterrent effect the threat of a perjury conviction has upon
No. 04-2406                                                 9

the conduct of government witnesses who to obtain a grant
of immunity might otherwise be inclined to lie.” United
States v. Kramer, 711 F.2d 789, 795 (7th Cir. 1983). Because
this line of inquiry was proper, there was no plain error. See
United States v. Mealy, 851 F.2d 890, 900 (7th Cir. 1988).


  2. Testimony Concerning Mohammed’s Safety
     Valve Reduction
  Johnson also claims that the government improperly
suggested that the court had already found Mohammed’s
testimony truthful as a matter of law based on proceedings
outside the jury’s presence. In introducing evidence of an
agreement, prosecutors may not imply that they possess
information not heard by the jury on the issue of the
immunized witness’s testimony. Mealy, 851 F.2d at 900. As
stated above, defense counsel alluded to Mohammed’s lack
of credibility during both voir dire questioning and opening
statement. In his opening, defense counsel stated that
Mohammed received a “benefit that was indirect . . . as a
result of his plea.” In cross-examining Mohammed, defense
counsel further intimated that the safety valve reduction
Mohammed received at sentencing depended on his pleas-
ing the government. On redirect, then, the government
sought to elicit those facts that defense counsel failed to
mention on cross-examination, including the four other
safety valve criteria and the court’s role in ultimately
determining Mohammed’s safety valve eligibility under
federal law. See U.S.S.G. § 5C1.2. The government at no
time argued that the jury should believe the witness
because the court found him truthful. Government ques-
tioning regarding the witness’s understanding of his
agreement with the government is proper. See Mealy, 851
F.2d at 900. Where defense counsel raises the issue of
sentencing and makes statements regarding the witness’s
agreement, the government may provide appropriate
10                                              No. 04-2406

clarification of any mischaracterization. United States v.
Sanchez, 251 F.3d 598, 603 (7th Cir. 2001). Here, because
the prosecutor merely placed the circumstances of Moham-
med’s safety valve sentencing into proper context, the
government’s conduct was proper.


  3. Closing Remarks Regarding Mohammed’s
     Truthfulness
  Johnson additionally argues that the prosecutor, in
closing argument, improperly suggested that the govern-
ment’s and the court’s actions ensured Mohammed’s
truthfulness. He first objects to the prosecutor’s recital in
closing of the circumstances of Mohammed’s appearing to
testify. The prosecutor described Mohammed’s initial
reluctance to testify and Judge Kennelly’s ensuing order of
immunity, which he said “takes away Kenny Mohammed’s
ability to assert the Fifth and forces him to come here and
tell you the truth. And that is exactly what he did.” The
prosecutor immediately thereafter detailed the substance of
Mohammed’s testimony and compared it to other evidence
that “corroborates what Kenny Mohammed told you from
the stand.” Also, when relating Mohammed’s testimony, the
prosecutor repeatedly intoned, “he told you the truth.”
  These remarks about the witness’s truthfulness, however,
are acceptable when placed in context with corroborating
evidence. For instance, in United States v. Morgan, this
Court found that the prosecutor did not inject his personal
opinion into the trial by characterizing the witness as “an
honest person.” 113 F.3d 85, 89 (7th Cir. 1997). Because the
comment was immediately preceded by the prosecutor’s
argument that corroborating evidence showed the witness
to be truthful, the prosecutor’s comment was “a permissible
inference from the evidence, not improper vouching.” Id. at
90. The same is true here. Where the government charac-
No. 04-2406                                                11

terizes a witness’s credibility “based on the evidence,” the
argument is proper because it is based on the record instead
of “the prosecutor’s own personal belief.” United States v.
Clarke, 227 F.3d 874, 884 (7th Cir. 2000). Because the
prosecutor premised Mohammed’s truthfulness on “all of
the evidence in this case” and stated that the jury must
“consider all of it together,” his remarks constituted a
permissible credibility argument based on the evidence, not
improper vouching based on his personal belief.
  Second, Johnson challenges the government’s later
remarks in closing to the effect that Mohammed “is here
under an order” and “understands he needs to tell the
truth” if he wanted to avoid a possible return to jail. Again,
though, where a prosecutor comments during closing
argument on a witness’s veracity but then follows with a
comparison to other evidence presented at trial, the com-
ment reflects “evidence presented at trial and not the
prosecutor’s personal opinion.” United States v. Goodapple,
958 F.2d 1402, 1410 (7th Cir. 1992). As described above, the
prosecutor in this case acted properly—he surveyed the
evidence corroborating Mohammed’s testimony and from
that evidence assessed his credibility. As in the following
example, the prosecutor’s closing argument portrayed
Mohammed as credible based on the evidence taken as a
whole:
    He told you the truth, and he told you that he got
    heroin from the defendant. He told you the truth, that
    he sold that heroin to Henry Adebayo, and he told you
    the truth, that he took the money from that sale and
    gave it to the defendant, the supplier of that heroin.
    That was the brokered transaction. You know that
    Kenny Mohammed told you the truth from all of the
    evidence in this case. The evidence in this case corrobo-
    rates what Kenny Mohammed told you from that stand.
12                                              No. 04-2406

The prosecutor then proceeded to summarize that corrobo-
rating evidence, discussing the recordings of Mohammed
receiving and making calls before the transactions, the
testimony of agents who witnessed the wine-colored Corolla
and Mohammed’s movements at both transactions, the
expert testimony of Agent Coleman regarding the typical
structure of these drug transactions, and the evasive moves
made by Johnson in the wine-colored Corolla. Thus, the
prosecutor properly argued that the evidence compelled the
conclusion that Mohammed complied with his immunity
agreement by testifying truthfully. See Clarke, 227 F.3d at
885 (holding that the prosecutor’s statement about a
witness’s truthfulness was proper “because the evidence
showed that [the witness] complied with the plea agree-
ment, not that [he] told the truth simply because he entered
into the plea agreement.”).
  Finally, Johnson challenges the prosecutor’s rebuttal
remarks again referencing the immunity order. One of
defense counsel’s arguments in closing was that “Kenny
Mohammed wasn’t telling the truth. He had every incentive
to lie.” In rebuttal, the prosecutor responded by arguing
that Mohammed understood “that he could be prosecuted
for perjury based on what he told you in Court today if it
turned out that what he said was not true,” and further
that “Kenny Mohammed has no incentive in this case to not
tell you the truth.” Yet again, however, the prosecutor
placed these remarks in context by telling the jury that it
“will be able to judge him . . . not only by what he said, but
also by the corroborating evidence,” which the prosecutor
then reviewed. Moreover, he specifically anticipated the
court’s instruction to the jury to consider the evidence “with
caution and care,” stating that “[t]he government asks that
you do that.” The government’s reference in closing argu-
ment to a witness’s truthfulness is proper so long as the
remarks are “tied to the evidence presented at trial or
reasonable inferences from that evidence,” rather than
No. 04-2406                                               13

personal opinion. United States v. Robbins, 197 F.3d 829,
843 (7th Cir. 1999). Our review of the record reveals that
the theory of the defense was to attack Mohammed’s
credibility. The defense argued in closing that Mohammed
“wasn’t telling the truth” and “had every incentive to lie,”
thus inviting a response from the prosecutor. See id. As a
result, the prosecutor’s comments in rebuttal were meant to
“right the scale” and were not improper. See id.


B. Sufficiency of the Evidence
  Johnson next asserts that the evidence presented at trial
was insufficient to establish beyond a reasonable doubt that
he was guilty of the conspiracy and possession counts. We
review a jury’s sufficiency of the evidence determination “in
the light most favorable to the government and uphold . . .
a jury’s decision if ‘any rational trier of fact could have
found the essential elements of the crime beyond a reason-
able doubt.’ ” United States v. Burke, 425 F.3d 400, 415 (7th
Cir. 2005) (quoting Jackson v. Virginia, 443 U.S. 307, 319
(1979)). We will indulge all reasonable inferences that
benefit the government. United States v. Sanchez, 251 F.3d
598, 601 (7th Cir. 2001). Because great deference is given to
the jury, a verdict will be overturned only if we find that
“the record contains no evidence, no matter how the
evidence is weighed, from which the jury could have found
guilt beyond a reasonable doubt.” Burke, 425 F.3d at 415.


  1. Conspiracy
  Under 21 U.S.C. § 846, a conspiracy exists where: “(1) two
or more people agreed to commit an unlawful act[;] and (2)
the defendant knowingly and intentionally joined in the
agreement.” United States v. Gardner, 238 F.3d 878, 879
(7th Cir. 2001). In order to support a conspiracy conviction,
the government must establish beyond a reasonable doubt
that there was a “combination or confederation between two
14                                                No. 04-2406

or more persons formed for the purpose of committing, by
their joint efforts, a criminal act.” United States v. Sullivan,
903 F.2d 1093, 1098 (7th Cir. 1990). The government must
establish that the defendant’s relationship with the other
conspirators was “more than a mere association.” Id. at
1098-99. An explicit agreement, however, is not required; a
jury can infer an agreement from the parties’ course of
dealing. Sanchez, 251 F.3d at 602.
  Johnson argues that the evidence of conspiracy was
insufficient because it proved only an ordinary buyer-seller
relationship between him and Mohammed, not a joint
conspiracy to sell heroin to Adebayo. Evidence that the
defendant was in a mere buyer-seller relationship with the
alleged coconspirator is insufficient to establish a conspir-
acy. See United States v. Rock, 370 F.3d 712, 714 (7th Cir.
2004). That remains true “even when the buyer intends to
resell the purchased narcotics.” United States v. Mims, 92
F.3d 461, 465 (7th Cir. 1996). There is sufficient evidence to
establish a conspiracy, however, where the jury finds
credible a government witness who shows that the alleged
coconspirators were “on the same side of the transaction.”
United States v. Smith, 393 F.3d 717, 720 (7th Cir. 2004).
  We will not upset the jury’s credibility determination
unless “exceptional circumstances” exist; that is, it was
“physically impossible for the witness to observe that which
he claims occurred, or impossible under the laws of nature
for the occurrence to have taken place at all.” Id. at 719.
Here, the events described by Mohammed were neither
physically impossible nor contrary to the laws of nature.
His testimony contained inconsistencies, to be sure—
Mohammed recalled the January 28 exchange occurring at
a different spot than the one remembered by the agents,
and the agents did not observe Mohammed enter the 7337
apartment building on February 16, as he remembered
doing. After defense counsel emphasized these contradic-
tions in closing argument and the court instructed the jury
No. 04-2406                                                 15

to consider them in assessing Mohammed’s testimony,
though, the jury still found Mohammed credible. As we
have said before, “it is not for us to second guess” the jury’s
credibility determination in a sufficiency challenge. United
States v. Smith, 34 F.3d 514, 521 (7th Cir. 1994).
  The evidence presented by the government was sufficient
to establish that the parties acted in concert, with the object
of distributing heroin to the third-party buyer in two
separate transactions. If Mohammed’s testimony is to be
believed, Mohammed contacted Johnson before the first
transaction to obtain the heroin for resale to the customer,
Adebayo. Johnson did not make Mohammed pay up front
but rather waited for Mohammed “to procure the money”
from the customer. See United States v. Smith, 393 F.3d
717, 720 (7th Cir. 2004). After the transaction, Mohammed
paid Johnson for the heroin, along with $250 as a brokering
commission, from the money he received from Adebayo.
  Before the February transaction, Mohammed again told
Johnson that his “guy,” the buyer, was ready. Afterwards,
he again paid Johnson from the sale proceeds, both for the
heroin and for the commission. The price, $100 per gram of
heroin, was the same for both transactions. Furthermore,
Agent Coleman’s expert testimony about the incentive
suppliers have to position themselves near brokered drug
deals corresponds with Johnson’s behavior in these two
instances. Taken together, this evidence of repeat sales, a
standardized course of dealing, and trust between the
parties was sufficient to establish that Mohammed and
Johnson “formed a continuing and mutually profitable
relationship to distribute drugs.” Sanchez, 251 F.3d at 602.
Because a reasonable jury could conclude that the two were
on the same side of the transaction, the evidence was
sufficient to establish a conspiracy. See United States v.
Smith, 393 F.3d 717, 720 (7th Cir. 2004).
16                                               No. 04-2406

  2. Possession
  Johnson similarly argues that the evidence presented by
the government was insufficient to establish that Johnson
possessed heroin. The government’s case against Johnson
depended heavily, though not exclusively, on Mohammed’s
testimony, described above. The principles described above
in reference to Mohammed’s credibility apply equally to
Johnson’s conviction on the possession counts. See United
States v. Smith, 34 F.3d 514, 521 (7th Cir. 1994). A reason-
able jury, crediting this testimony, could infer that Johnson
possessed and transferred heroin to Mohammed in ex-
change for money. Additionally, the government presented
substantial evidence corroborating Johnson’s possession.
Agents observed a wine-colored Toyota Corolla with tinted
windows and Texas license plates at both the January 28
transaction and the February 16 transaction. Immediately
after the first transaction, agents observed the car en-
gage in an evasive counter-surveillance excursion from the
south side to the north side of Chicago. In the same automo-
bile, Johnson engaged in an erratic and high-speed flight
from agents shortly after the second transaction. Agents
recovered from Johnson the cash, identified unmistakably
by serial number, provided to Adebayo earlier that day to
purchase heroin from Mohammed. Together, Mohammed’s
testimony and the corroborating evidence provided suffi-
cient evidence to support Johnson’s possession conviction.
See United States v. Smith, 393 F.3d 717, 719 (7th Cir.
2004).


C. Buyer-Seller Defense Instruction
  Johnson also claims that the district court erred by failing
to instruct the jury sua sponte that repeat drug sales alone
do not constitute a conspiracy. Because Johnson did not
tender a buyer-seller instruction or object to its omission,
we review for plain error. United States v. Askew, 403 F.3d
No. 04-2406                                                 17

496, 502-03 (7th Cir. 2005). To reverse a conviction under
the plain error standard, we must find that: (1) an error
occurred; (2) it was “plain,” meaning obvious or clear; (3) it
affected the defendant’s substantial rights; and (4) it
seriously affected the fairness, integrity, or public reputa-
tion of the judicial proceedings. Id. (quoting United States
v. Gibson, 356 F.3d 761, 765-66 (7th Cir. 2004)). District
courts should instruct juries that repeat transactions by
themselves do not constitute a conspiracy only if “the
instruction has some foundation in the evidence.” United
States v. Douglas, 818 F.2d 1317, 1320 (7th Cir. 1987).
  In assessing the propriety of giving the instruction, we
consider whether the defendant put forth a buyer-seller
theory at trial. Askew, 403 F.3d at 503. Finding no error in
Askew, this Court noted that the defendant’s trial strategy,
denying any involvement with drugs instead of asserting a
buyer-seller defense, “cuts in favor of finding no error in the
district judge’s decision not to give the instruction.” Id. at
504. Here, as in Askew, it is undisputed that Johnson did
not advance a buyer-seller theory of defense. He argued
instead that he was “not a drug dealer” and so could not
have supplied Mohammed with heroin for the two transac-
tions. The strength of the evidence indicating a conspiracy,
combined with Johnson’s decision at trial not to pursue a
buyer-seller theory of defense, leads to our conclusion that
the district court did not commit plain error by declining to
give the instruction sua sponte. See Askew, 403 F.3d at 504-
05.


D. Intimidation of Defense Witness
  Johnson further alleges that the government denied him
constitutional due process by threatening investigation and
indictment of a defense witness, Witness A, to prevent her
from testifying. We review allegations of prosecutorial
threatening of defense witnesses for abuse of discretion,
18                                               No. 04-2406

which arises where the prosecutor “intends to use his
authority to distort the judicial fact-finding process.” United
States v. Hooks, 848 F.2d 785, 799 (7th Cir. 1988). A
fundamental element of due process is the right of the
accused to present witnesses in his own defense. Id. (citing
Washington v. Texas, 388 U.S. 14 (1967)). Defense witnesses
must be free to testify without fear of governmental retalia-
tion. United States v. Burke, 425 F.3d 400, 411 (7th Cir.
2005). The defendant’s right to present witnesses, however,
is tempered by the witness’s Fifth Amendment privilege not
to provide incriminating testimony. United States v. George,
363 F.3d 666, 671 (7th Cir. 2004). A prosecutor may
therefore caution a defense witness about the risks of
testifying, but “[w]here . . . the substance of what the
prosecutor communicates to the witness is ‘a threat over
and above what the record indicate[s] was timely, neces-
sary, and appropriate,’ the inference that the prosecutor
sought to coerce a witness into silence is strong.” United
States v. Jackson, 935 F.2d 832, 847 (7th Cir. 1991) (quoting
United States v. Simmons, 670 F.2d 365, 369 (D.C. Cir.
1982)).
  At trial Johnson wanted Witness A to testify that she had
given Johnson $5,950, the amount seized by Officer Sapp
from Johnson’s car, so that Johnson could purchase a car on
her behalf. When she initially told agents that account in
February 2000, they gave her the money in order to keep
the investigation “covert.” Witness A was arrested and
indicted approximately a year later. Although Johnson now
describes this complaint as “flimsy,” the government is
correct in presuming that Witness A would have a difficult
time explaining how money that supposedly belonged to her
bore the serial numbers of bills that agents had given to
Adebayo to purchase heroin. In fact, she admitted while in
custody that Johnson had paid her $200 to fabricate the
story. As a result, the criminal complaint was dismissed
without prejudice because the government “expected her to
No. 04-2406                                                19

be a cooperating witness.” In fall 2003, shortly before the
trial was scheduled to begin, because she again reverted to
her original account of events, the government understand-
ably designated her a subject of investigation once again. In
response to the defendant’s subpoena, Witness A invoked
her Fifth Amendment privilege against self-incrimination.
  The government announced its changed position in the
following letter to defense counsel:
    Witness A is currently the possible subject or target of
    an investigation concerning false statements and/or
    obstruction of justice concerning her statements on
    February 24, 2000, and she may be charged with a
    crime. The U.S. Attorney’s Office currently has not
    provided Witness A with any consideration or promises
    of consideration.
Significantly, this announcement was made to Johnson and
his counsel, not to Witness A. The fact that the disputed
language appeared in a court-ordered letter to defense
counsel, a rather inefficient medium for conveying threats
to a witness, suggests that it probably was not intended to
deter Witness A from testifying. After all, this line of cases
focuses on “what the prosecutor communicates to the
witness.” Jackson, 935 F.2d at 847.
  The government’s messages to a witness, conveyed
through defense counsel, have in the past been held to be
improper threats. See, e.g., United States v. Morrison, 535
F.2d 223, 225-26 (3d Cir. 1976). In Morrison, however, the
prosecutor’s conduct was far more flagrant; he sent mes-
sages to the witness through defense counsel on three
occasions communicating “that she was liable to be prose-
cuted on drug charges; that if she testified, that testimony
would be used as evidence against her and, further, that as
she was now eighteen it would be possible to bring federal
perjury charges against her.” Id. at 225. The prosecutor
20                                               No. 04-2406

further subpoenaed the witness and had her brought into
his office for a meeting with three undercover agents to
impress on her again the dangers of testifying. Id.
  The letter sent by the government in this case does not
approximate the actions taken by the prosecutor in Morri-
son. Here, the letter conveyed accurate information about
the risks Witness A faced by testifying, and contained a
single warning instead of several. Where the prosecution
simply presents the facts to the witness, informing him that
he is the target of an investigation and providing him with
a warning, no constitutional violation occurs. Jackson, 935
F.2d at 847. Moreover, no evidence indicated that the letter
sent to defense counsel was intended as a message to
Witness A; to the contrary, the government sent the letter
to comply with a court order requiring disclosure of im-
peachment evidence. Because the letter was not directed to
Witness A and none of its language can fairly be construed
as overreaching or improper intimidation, there is no basis
in the record from which to conclude that the government
improperly threatened her, procured her unavailability, or
caused her to invoke the privilege. On the contrary, the
government had a reasonable basis to believe that Witness
A was a possible subject of prosecution. The court accord-
ingly considered her assertion of the Fifth Amendment
privilege in light of the “plainly incriminating nature of the
proposed testimony.” George, 363 F.3d at 671. Thus, John-
son’s right to present a defense was not violated by Witness
A’s invocation of her Fifth Amendment privilege.


E. Limited Remand
  Finally, Johnson challenges his sentence, asserting that
the court’s mandatory application of the Guidelines made
the sentence improper. In United States v. Booker, the
Supreme Court held that “the Sixth Amendment as con-
strued in Blakely does apply to the Sentencing Guidelines.”
No. 04-2406                                               21

125 S.Ct. 738, 746 (2005). Accordingly, “[a]ny fact (other
than a prior conviction) which is necessary to support a
sentence exceeding the maximum authorized by the facts
established by a plea of guilty or a jury verdict must be
admitted by the defendant or proved to a jury beyond a
reasonable doubt.” Id. at 756. Because the court based
Johnson’s enhancement on his statements at the suppres-
sion hearing, none of the relevant facts were found by a
jury. Moreover, the parties do not dispute that at the time
of defendant’s May 2004 sentencing, the district court
regarded the Sentencing Guidelines as mandatory.
  Because the Supreme Court rendered the Guidelines
advisory, “the mere mandatory application of the Guide-
lines—the district court’s belief that it was required to
impose a Guidelines sentence—constitutes error.” United
States v. White, 406 F.3d 827, 835 (7th Cir. 2005) (citing
Booker, 125 S.Ct. at 769). It is impossible to say whether
the court would have imposed the same sentence knowing
that the Guidelines were advisory. Therefore, we order a
limited Paladino remand to determine whether the district
court, treating the Guidelines as advisory, would reimpose
the same sentence. See United States v. Paladino, 401 F.3d
471, 484 (7th Cir. 2005).


                     III. Conclusion
  For the foregoing reasons, we AFFIRM Johnson’s convic-
tion. While retaining jurisdiction, we remand to the district
court for proceedings consistent with Paladino, 401 F.3d at
483-84.
22                                        No. 04-2406

A true Copy:
      Teste:

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




               USCA-02-C-0072—2-10-06
