                       PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,
               v.                          No. 12-4168
RAYMOND DANGELO ALLEN,
             Defendant-Appellant.
                                      
        Appeal from the United States District Court
  for the Western District of North Carolina, at Asheville.
           Martin K. Reidinger, District Judge.
                (1:10-cr-00066-MR-DLH-1)

                 Argued: March 22, 2013

                  Decided: April 26, 2013

Before KING, GREGORY, and KEENAN, Circuit Judges.



Affirmed in part, vacated in part, and remanded by published
opinion. Judge Gregory wrote the opinion, in which Judge
King and Judge Keenan joined.


                        COUNSEL

ARGUED: Aaron Edmund Michel, Charlotte, North Caro-
lina, for Appellant. Amy Elizabeth Ray, OFFICE OF THE
UNITED STATES ATTORNEY, Asheville, North Carolina,
for Appellee. ON BRIEF: Anne M. Tompkins, United States
2                   UNITED STATES v. ALLEN
Attorney, Charlotte, North Carolina, Richard Lee Edwards,
Assistant United States Attorney, OFFICE OF THE UNITED
STATES ATTORNEY, Asheville, North Carolina, for Appel-
lee.


                          OPINION

GREGORY, Circuit Judge:

   In June 2010, law enforcement uncovered an extensive
crack cocaine distribution network operating in Buncombe
and McDowell counties, North Carolina. For his part in the
enterprise, Raymond Allen was convicted by a federal jury in
the Western District of North Carolina of conspiring to pos-
sess fifty grams or more of cocaine base with intent to distrib-
ute, in violation of 21 U.S.C. §§ 841(a)(1) and 846. As a
result, Allen was sentenced to ten years’ imprisonment, the
mandatory minimum sentence in effect at the time he alleg-
edly committed the offense. Allen now challenges his convic-
tion, arguing there was insufficient evidence to support his
knowledge of the drug ring. Further, he charges that the dis-
trict court erred in denying his pretrial motions, and thus his
conviction should be vacated. Finally, Allen argues the dis-
trict court erred in imposing the ten-year mandatory minimum
sentence given that Congress passed the Fair Sentencing Act
of 2010, Pub. L. No. 111-220, 124 Stat. 2372, prior to his sen-
tencing. For the reasons that follow, we affirm Allen’s con-
viction but vacate his sentence and remand to the district court
for resentencing.

                               I.

   On October 5, 2010, Raymond Allen was one of eleven
defendants named in a fifteen-count indictment. Five addi-
tional co-conspirators were also named in the indictment.
Allen was charged with one count of conspiring to possess
                    UNITED STATES v. ALLEN                   3
fifty grams or more of cocaine base with intent to distribute,
in violation of 21 U.S.C. §§ 841(a)(1) and 846. The indict-
ment was the result of an extensive investigation that took
place between January and June of 2010. Prior to the start of
trial, Allen made two pretrial motions relevant to this appeal.
First, Allen moved to see his codefendants’ Presentence
Reports (PSR) and sealed sentencing memoranda. The district
court denied the motion in a written order. Second, Allen
moved to call a criminal defense expert to help explain the
potential significance of all of the indicted codefendants
reaching plea agreements with the government. The court
orally denied the motion.

                              A.

   Trial was held from June 27 to June 29, 2011. The evidence
adduced revealed a multi-tiered crack cocaine distribution
ring operating in Western North Carolina. As proof of the
extensive operation, the government called twenty-seven wit-
nesses, including thirteen law enforcement officers, three con-
fidential informants, three codefendants, and five separately
identified co-conspirators. The government also introduced
recordings of telephone calls, photographs, and videotapes.

   The mountainous evidence showed that the drug network
operated in the following manner. The bottom link of the drug
distribution chain consisted of approximately ten street-level
dealers. The street dealers sold $5 and $20 crack rocks in low-
income neighborhoods. These street dealers would buy the
crack cocaine from three suppliers higher up in the distribu-
tion chain. The second-rung suppliers would in turn buy crack
cocaine from Chrissawn Folston. Finally, Folston would buy
his supply of crack cocaine from Willie Chappell, who sup-
plied the drug to him in bulk. The government further claimed
that when Chappell was unable to supply crack cocaine, Fols-
ton turned to Allen as the back-up supplier.

  Allen does not dispute that the evidence introduced at trial
sufficiently detailed this operating scheme. He admits that the
4                   UNITED STATES v. ALLEN
drug network was "substantial and involved most of the ten
codefendants, five named co-conspirators, and other named
conspirators." Appellant’s Br. 37. Allen does dispute, how-
ever, the government’s assertion at trial that when Chappell
was unable to supply crack cocaine to Folston, Folston would
turn to him as a back-up supplier. This brings us to the events
that provided the basis for Allen’s arrest.

                              B.

   On May 17, 2010, Folston tried to purchase crack cocaine
from Chappell, but Chappell was unable to deliver. Folston,
therefore, called Allen and placed an order for two ounces of
the drug. Allen quoted Folston a price of $950 an ounce and
told him to meet him at his mother’s house in Asheville,
North Carolina. Folston’s girlfriend, Robin Anderson, drove
him to Allen’s mother’s house. Folston successfully pur-
chased the crack cocaine from Allen.

   When Folston got home, he weighed his purchase and real-
ized he only received one-and-a-half ounces of crack cocaine
instead of the two ounces for which he paid. He called Allen
to complain, at which point Allen told him that the next time
Folston needed a supply he would reconcile the discrepancy.
Placated, Folston went about selling the crack cocaine to the
second-rung suppliers, who in turn sold the drug to the street
dealers for distribution.

  The next day, May 18, Folston again called Allen, request-
ing another two ounces of crack cocaine, but in order to make
up for the day before, Folston told Allen that he was only
going to pay for an ounce and a half. Allen agreed and told
Folston to again meet him at his mother’s house. Robin
Anderson drove Folston to Asheville for a second time.
Although Allen was not there when Folston arrived, Folston
eventually purchased the crack cocaine from Allen at a nearby
apartment complex.
                    UNITED STATES v. ALLEN                     5
   As it turns out, Folston’s girlfriend, Robin Anderson, was
a government informant. The police, therefore, had placed a
GPS tracking device on her vehicle and were able to physi-
cally follow her. They therefore observed Folston buying and
selling crack on multiple occasions, including the two transac-
tions between him and Allen. Thus, all of the above events
were testified to by Anderson, law enforcement officials who
conducted surveillance, and Folston himself. As such, Allen
does not attempt to allege that there was insufficient evidence
to prove the two buy-sell transactions between him and Fols-
ton.

   The government also introduced testimony that while Allen
was detained awaiting trial, he had a conversation with a
street dealer named Wilkerson, who lamented to Allen that
they would all "be partying" if the other street dealers had
"kept their mouths shut and hadn’t told on everyone and got
all this stuff started." Allen supposedly replied to this by say-
ing: "You got that right. She the one that got me, too. Set me
up." For clarity, Wilkerson asked: "Who? Robin [Anderson]?"
Allen replied: "You got that right." The government asserted
that this conversation was relevant as it showed that Allen
was aware of the drug distribution network.

                               C.

   At the close of the government’s case-in-chief, Allen
moved for judgment of acquittal. The court and the govern-
ment engaged in a discussion concerning the evidence pre-
sented to the jury, particularly the evidence linking Allen to
the conspiracy. Allen alleged that while the government may
have proven that he was involved in two buy-sell transactions,
it did not prove beyond a reasonable doubt that he participated
in or had any knowledge of the overarching conspiracy. The
district court considered the argument and denied the motion.
Allen put on no evidence and renewed the motion at the end
of trial, which the district court again denied. The jury found
Allen guilty. Ten days later, Allen filed a renewed motion for
6                   UNITED STATES v. ALLEN
judgment of acquittal. The court denied the motion, issuing a
written memorandum and order. See United States v. Allen,
No. 1:10-cr-66-1 (W.D.N.C. Aug. 3, 2011).

   Allen timely appealed, arguing: (1) there was insufficient
evidence for a jury to find him guilty of conspiracy to distrib-
ute; (2) the district court erred by denying him access to his
codefendants’ PSRs and by refusing his expert testimony; and
(3) the district court erred in sentencing him in accordance
with the statutory mandatory minimum given that the thresh-
old amount of crack cocaine necessary for the mandatory
minimum was raised by the Fair Sentencing Act prior to his
sentencing.

                               II.

   We review the district court’s denial of a motion for judg-
ment of acquittal de novo. United States v. Lentz, 383 F.3d
191, 199 (4th Cir. 2004). Given that Allen is challenging the
sufficiency of the evidence presented to the jury, we view the
evidence presented at trial in the light most favorable to the
government and will sustain the verdict if we find that any
rational factfinder could find the elements of the crime
beyond a reasonable doubt. See United States v. Burgos, 94
F.3d 849, 854 (4th Cir. 1996) (en banc).

   To be found guilty of conspiracy to distribute crack
cocaine, the government must prove: (1) an agreement to pos-
sess crack cocaine with intent to distribute between two or
more persons; (2) the defendant knew of the conspiracy; and
(3) the defendant knowingly and voluntarily became a part of
the conspiracy. See United States v. Strickland, 245 F.3d 368,
384-85 (4th Cir. 2001). A conspiracy may "be proved wholly
by circumstantial evidence." Burgos, 94 F.3d at 858. And,
"one may be a member of a conspiracy without knowing its
full scope, or all its members, and without taking part in the
full range of its activities or over the whole period of its exis-
tence." United States v. Banks, 10 F.3d 1044, 1054 (4th Cir.
                    UNITED STATES v. ALLEN                   7
1993); see also United States v. Brooks, 662 F.2d 1138, 1147
(4th Cir. 1992) ("[A] defendant need not have had knowledge
of his co-conspirators . . . or knowledge of the details of the
conspiracy."). Therefore, "[o]nce a conspiracy has been
proved, the evidence need only establish a slight connection
between any given defendant and the conspiracy to support
conviction." Strickland, 245 F.3d at 385.

   We will uphold a conspiracy conviction even if the defen-
dant’s involvement is minimal. See, e.g., Brooks, 957 F.2d at
1147; United States v. Seni, 662 F.2d 277, 285 n.7 (4th Cir.
1991). We have also "reiterate[d] that the focus of a conspir-
acy charge is the agreement to violate the law, not whether the
conspirators have worked out the details of their confederated
criminal undertakings." United States v. Mills, 995 F.2d 480,
484 (4th Cir. 1993). As such, our precedent is unambiguous
in that a defendant may be convicted of conspiracy to distrib-
ute even if the evidence shows "participation in only one level
of the conspiracy charged in the indictment." United States v.
Lewis, 54 F.3d 1150, 1154 (4th Cir. 1995) (citation omitted).

  The government undisputedly proved a multi-tiered crack
cocaine distribution conspiracy. Allen’s argument therefore
hinges on his assertion that the government did not prove his
knowledge of the conspiracy, and instead, only put on evi-
dence that he sold 3.5 ounces of crack cocaine to Folston.
Allen argues that the evidence only shows two independent
buy-sell transactions, which does not equate to knowledge of
a broader conspiracy.

   Our precedent short-circuits Allen’s argument. Indeed, we
have said that evidence of the sale of crack cocaine on its own
is too thin to support an inference of conspiracy. See United
States v. Edmonds, 679 F.3d 169, 174 (4th Cir. 2012), judg-
ment vacated on other grounds, 133 S. Ct. 376 (2012) ("[T]he
mere evidence of a simple buy-sell transaction is sufficient to
prove a distribution violation under § 841, but not conspiracy
under § 846."); United States v. Thomas, 489 F. App’x 688,
8                   UNITED STATES v. ALLEN
691 (4th Cir. 2012) (unpublished per curiam), cert. denied,
133 S. Ct. 588 (2012). But we have also stated that a single
buy-sell transaction "is at least relevant (i.e. probative) on the
issue of whether a conspiratorial relationship exists." Mills,
995 F.2d at 485 n.1; United States v. Hackley, 662 F.3d 671,
679 (4th Cir. 2011). Additionally, evidence of a defendant
buying or selling a substantial quantity of drugs over a short
period of time is enough to raise an inference of a distribution
conspiracy. United States v. Reid, 523 F.3d 310, 317 (4th Cir.
2008) ("[E]vidence of a buy-sell transaction . . . coupled with
a substantial quantity of drugs, would support a reasonable
inference that the parties were coconspirators.").

   At trial, the government put on evidence that the 3.5 ounces
(99.2 grams) of crack cocaine that Allen sold Folston was
enough to produce over 1000 crack rocks. Given that we have
upheld convictions for intent to distribute charges for amounts
much less than that involved here, see, e.g., United States v.
Lamarr, 75 F.3d 964, 973 (4th Cir. 1996) (5.72 grams), it is
fair to conclude that a reasonable juror could infer that when
Allen sold Folston such a substantial quantity of crack
cocaine over the course of two days, Allen knew the drug was
going to be further distributed. It is hard to fathom that one
would purchase in short order the equivalent of 1000 crack
rocks for personal use.

   Thus, viewing the evidence in the light most favorable to
the government, the evidence of the two consecutive buy-sell
transactions, both of which involved substantial amounts of
crack cocaine, was enough to support a conspiracy to distrib-
ute conviction. This conclusion is further buttressed by
Allen’s jailhouse conversation, which indicates that Allen was
at least somewhat cognizant that the distribution scheme in
question was larger than the two buy-sell transactions of
which he was a part. We affirm Allen’s conspiracy to distrib-
ute conviction.
                    UNITED STATES v. ALLEN                      9
                               III.

   Next, Allen makes two charges of error in regards to the
district court’s pretrial evidentiary rulings. First, Allen argues
the district court erred by refusing to grant him permission to
see his codefendants’ PSRs. And second, he argues the dis-
trict court erred by denying him the use of expert testimony
to help explain the ramifications of his codefendants’ plea
agreements with the government. We review the district
court’s evidentiary rulings, including the decision to review a
codefendant’s PSR, for abuse of discretion. United States v.
Trevino, 89 F.3d 187, 193 (4th Cir. 1996).

                               A.

   PSRs have "always been jealously guarded . . . by the fed-
eral courts." Trevino, 89 F.3d at 192. Before a district court
can grant a defendant’s request to view a codefendant’s PSR,
therefore, the district court must perform an in camera review
of the PSR. Id. This in camera review is not mandatory, how-
ever. The district court need only perform the in camera
examination once the defendant has "clearly specified the
information contained in the report that he expects will reveal
exculpatory or impeachment evidence." Id. Thus, "as a pre-
requisite for an in camera review, an accused must plainly
articulate how the information contained in the PSR will be
both material and favorable to his defense." Id. at 192-93.

   When Allen requested the PSRs and sentencing memo-
randa for his codefendants, he based his argument on the
unsealed sentencing memorandum of one codefendant, Bran-
don Michael Walker. Walker’s sentencing memorandum
revealed that his PSR recommended that 361.1 grams of crack
cocaine be found attributable to him for sentencing. By con-
trast, the government’s sentencing memorandum recom-
mended that Walker be held responsible for at least 1.4 grams
of crack cocaine but less than 2.8 grams. The difference in
amounts had the effect of reducing Walker’s sentence range
10                  UNITED STATES v. ALLEN
from 97-121 months to 12-18 months. Using Walker as an
example, Allen asserted that he was "entitled to know what
other ‘sweetheart deals’ his alleged codefendants and alleged
co-conspirators have received, as such information is directly
related to their bias, motivation, and credibility." Allen
believed that the large discrepancy in the amount of crack
cocaine attributed to Walker in his PSR versus the requested
amount in the government’s sentencing memorandum was
evidence of the government trading jail-time for testimony.
Therefore, Allen wanted to know if similar agreements were
reached by other codefendants.

   Applying the standard outlined in Trevino, the district court
did not find Allen’s reasons as to why he needed access to his
codefendants’ PSRs compelling enough to conduct an in cam-
era review, and subsequently denied Allen’s motion. The dis-
trict court declared that Allen did not identify any specific
information in the PSRs and sentencing memoranda that
would be material or favorable to his defense. The court
explained that contrary to Allen’s assertions, Walker did not
receive a "sweetheart deal." The lower amount of crack
cocaine reflected in Walker’s sentencing memorandum was
the amount of the crack cocaine that he sold directly, versus
the PSR amount which reflected the amount of crack cocaine
involved in the larger conspiracy, thus vitiating Allen’s argu-
ment. The district court also noted that the codefendants
would all be called as government witnesses at trial and there-
fore could be cross-examined regarding their plea agreements
or any promises of leniency.

   It is true that evidence of a "sweetheart deal" is relevant to
a witness’s credibility. See Campbell v. Reed, 594 F.2d 4, 7
(4th Cir. 1979). However, this does not mean that a defendant
can go on a fishing expedition every time a codefendant
pleads guilty, as Trevino clearly requires a specific explana-
tion of what exculpatory evidence a PSR will contain. 89 F.3d
at 192-93. For the reasons stated by the district court, Allen’s
conclusory claims did not meet this threshold when he moved
                    UNITED STATES v. ALLEN                    11
for access to the PSRs. The district court did not abuse its dis-
cretion by denying Allen’s motion and refusing to conduct an
in camera review of the codefendants’ PSRs.

                               B.

   Turning to Allen’s motion to admit expert testimony, in
order for expert testimony to be admissible, two requirements
must be met: (1) the testimony must involve scientific, techni-
cal, or other specialized knowledge, and (2) the testimony
must aid the trier of fact to help understand or resolve a fact
issue. Fed. R. Evid. 702. Allen wanted to use an expert crimi-
nal defense attorney to explain the legal significance of
§ 5K1.1 letters, § 3553(e) motions, and 21 U.S.C. § 851
notices—all of which entail the government asking for a
lesser sentence in light of a defendant’s substantial
cooperation—in order to show that the codefendants called to
testify against him may be biased. The district court denied
the motion after conducting a hearing in limine, reasoning that
Allen could ask for a clarifying instruction if the testimony
regarding the codefendants’ plea process was too complex.
The court refused to allow a separate expert to testify, how-
ever, as that would effectively "supplant" the court’s function.

   We find that the district court did not abuse its discretion
in denying this motion. Essentially, Allen wanted to introduce
expert testimony solely for the purpose of undermining the
credibility of the codefendant witnesses. This is not the func-
tion of an expert. See Nimely v. City of New York, 414 F.3d
381, 398 (2d Cir. 2005) (holding "that expert opinions that
constitute evaluations of witness credibility, even when such
evaluations are rooted in scientific or technical expertise, are
inadmissible under Rule 702"). A juror can connect the dots
and understand the implications that a plea agreement might
have on a codefendant’s testimony — "it is certainly within
the realm of common sense that certain witnesses would have
an incentive to incriminate the defendant in exchange for a
lower sentence." United States v. French, 12 F.3d 114, 117
12                  UNITED STATES v. ALLEN
(8th Cir. 1993). This is not an issue of fact that would be bet-
ter explained by an expert.

   Given the nature of the requested expert testimony, the dis-
trict court did not err in denying Allen’s motion to admit
expert testimony. Expert testimony of this nature is not per-
mitted under the Federal Rules of Evidence. Moreover, in an
abundance of caution, the district court admonished the jury
to examine more carefully the testimony of witnesses that
may be motivated by the desire to escape punishment. Finding
no error in the district court’s rulings on Allen’s pretrial
motions, we see nothing in the record that warrants vacating
Allen’s conspiracy conviction.

                              IV.

   Allen finally argues that the district court erred by applying
the ten-year mandatory minimum sentence for offenses
involving fifty or more grams of crack cocaine, given that the
threshold amount for the mandatory minimum to apply was
raised to 280 grams by the Fair Sentencing Act prior to his
sentencing. Whether the new threshold amount announced in
the Fair Sentencing Act applied to Allen is a question of law
which we decide de novo. United States v. Ide, 624 F.3d 666,
668 (4th Cir. 2010).

   At sentencing, Allen’s Guidelines range, with an offense
level of twenty-six and criminal history category of III, was
calculated to be seventy-eight to ninety-seven months. Allen’s
PSR recommended the mandatory minimum of ten years be
imposed, as the mandatory minimum would have applied at
the time Allen committed the crime. See 21 U.S.C.
§ 841(b)(1)(A) (2009) (amended 2010) (providing for a ten-
year mandatory minimum sentence for offenses involving
more than fifty grams of crack cocaine). Therefore, the PSR
recommended sentence was 120 months. Allen objected to the
PSR, arguing that the court should follow the newly enacted
Fair Sentencing Act, which increased the threshold amount of
                    UNITED STATES v. ALLEN                   13
crack cocaine necessary for the mandatory minimum from 50
grams to 280 grams. Given that his offense involved 3.5
ounces (99.2 grams) of crack cocaine, Allen argued he did not
meet the new threshold amount, and therefore was ineligible
for the ten-year mandatory minimum sentence.

   The district court rejected Allen’s argument, applying our
decision in United States v. Bullard, 645 F.3d 237, 248 (4th
Cir. 2011), in which we held that the Fair Sentencing Act
does not apply retroactively. Thus, because the lower thresh-
old amount for the mandatory minimum was in force at the
time Allen committed the offense, the district court found that
Bullard controlled and the mandatory minimum applied.
Allen was sentenced to the mandatory minimum of 120
months on February 16, 2012.

   While the district court may have correctly applied our pre-
cedent at the time it reached its decision, our holding in Bul-
lard has since been limited by the recent Supreme Court
decision in Dorsey v. United States, 132 S.Ct. 2321 (2012). In
Dorsey, the Court held that "Congress intended the Fair Sen-
tencing Act’s more lenient penalties to apply to those offend-
ers whose crimes preceded August 3, 2010 [the date the Fair
Sentencing Act was enacted], but who are sentenced after that
date." Id. at 2331. As the government concedes, the Fair Sen-
tencing Act therefore applies to all sentences imposed after its
enactment, regardless of when the underlying crime was com-
mitted. Thus, our holding in Bullard—that the Fair Sentenc-
ing Act does not have retroactive effect—is limited to the
extent that the Fair Sentencing Act does apply to all sentences
handed down after its enactment.

   Because the Fair Sentencing Act was passed before Allen
was sentenced and Allen did not possess 280 grams of crack
cocaine necessary for the ten-year mandatory minimum sen-
tence to apply under the Fair Sentencing Act, the district court
erred by sentencing Allen to the mandatory minimum. We
14                  UNITED STATES v. ALLEN
therefore vacate Allen’s sentence and remand the case for
resentencing.

                              V.

   To conclude, we find that Allen’s conviction of conspiracy
to possess crack cocaine with the intent to distribute was well
supported by substantial evidence. Further, the district court
committed no error in its pretrial evidentiary rulings. How-
ever, we vacate Allen’s sentence and remand the case to the
district court for resentencing because Allen is ineligible for
the ten-year mandatory minimum sentence imposed.

                                       AFFIRMED IN PART,
                                        VACATED IN PART,
                                          AND REMANDED
