                             In the

United States Court of Appeals
              For the Seventh Circuit

No. 08-2979

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

L ONNIE D. M ORRIS,
                                              Defendant-Appellant.


            Appeal from the United States District Court
       for the Northern District of Illinois, Western Division.
              No. 06 CR 50007—James B. Zagel, Judge.



      A RGUED JUNE 2, 2009—D ECIDED A UGUST 10, 2009




 Before P OSNER, R IPPLE, and K ANNE, Circuit Judges.
  K ANNE, Circuit Judge. In 2007, a jury convicted Lonnie
Morris of drug and firearm offenses. On appeal, he chal-
lenges the sufficiency of the evidence, the jury instruc-
tions, and the admission of certain expert testimony.
We affirm his conviction.


                       I. B ACKGROUND
  In late May 2005, authorities began investigating sus-
pected drug trafficking activities at 707 Albert Avenue, a
2                                            No. 08-2979

residence on the west side of Rockford, Illinois. The
investigation was conducted by the Metro Narcotics
Unit, a joint enterprise between the Rockford Police
Department and the Winnebago County Sheriff’s De-
partment. Sergeant Marc Welsh supervised the MNU.
  Between five and ten times from May 22 to June 2,
Richard Gambini, a detective with the MNU, surveilled
707 Albert. The house was leased by Tamica Wilson, who
lived there with her two children. On at least five occa-
sions, Gambini observed the defendant, Lonnie Morris,
on or near the premises. Morris was frequently seen
coming and going in a maroon-colored 1995 Chrysler
Cirrus.
  Early in the morning on June 2, Gambini and a
colleague searched trash bags that were left on the curb
in front of 707 Albert. Inside, they found approximately
three hundred plastic sandwich bags with the bottoms
cut off; remnants of a package of Dormin, an over-the-
counter sleeping pill commonly used to “cut,” or dilute,
heroin for sale; and a handful of documents sent to
Lonnie Morris’s attention at a different address.
  Later that day, Gambini returned to 707 Albert with a
search warrant for both the house and the Chrysler
Cirrus. Gambini drove by the home and elected not to
execute the warrant at that time because the Cirrus
was not parked at the house.
  Within minutes, Gambini found the Cirrus in a liquor
store parking lot a short drive from 707 Albert. Morris
was in the driver’s seat, alone in the car. As Gambini
watched, an individual approached Morris’s car window,
No. 08-2979                                             3

where the two engaged in a short conversation and ex-
changed unidentifiable items.
   Following this first exchange, Morris drove the Cirrus
out of the parking lot. Gambini followed. After driving
for several blocks, Morris pulled the car to the curb near
an intersection. The scene from the liquor store repeated
itself. A different individual approached the car, spoke
with Morris through the driver’s window, and engaged
in a hand-to-hand exchange with Morris. Again, Gambini
was unable to identify the items that the men exchanged.
  From there, Morris, with Gambini still on his tail, pro-
ceeded to 707 Albert. Morris parked the Cirrus in the
driveway but remained in the car. A short time later, a
second car pulled into the driveway behind the Cirrus.
The driver of the second car emerged and walked to
the Cirrus, where he had a short discussion with Mor-
ris. For a third time, Morris handed something to the
individual through the driver’s window, received some-
thing in return, and the man departed. Morris then
entered the house.
  At that point, Gambini summoned his team to execute
the warrant on 707 Albert. Within ten minutes, the
MNU raid squad arrived and entered the premises
through its back door. Gambini, who was the last one
through the door, heard someone running up a set of
stairs located to his right that led to the home’s base-
ment. He moved to the top of the stairs and observed
Morris scaling the last few steps before running through
the door and out of the house. An officer stationed
outside tackled Morris.
4                                              No. 08-2979

  In the basement of the house, officers found a washer
and dryer, a cellular telephone, a razor blade, a digital
scale, and two empty plastic sandwich bags. In addition
to random debris, the basement contained a mattress
leaned against a corner wall. Behind the mattress, the
search team found a one-gallon plastic bag containing a
chunky, brown, powdery substance that was later identi-
fied as 23.6 grams of heroin. Officers searched the
entire residence but found no tangible evidence linking
Morris to the house.
  Police also discovered pertinent evidence inside the
Chrysler Cirrus. In the door’s handle well, Detective
Gambini found a small plastic bag, inside of which were
two smaller plastic bags. The two smaller plastic bags
contained an off-white powdery substance, later
identified as a total of 0.09 grams of a mixture containing
heroin. Underneath the bag with the heroin, Gambini
found another plastic bag, in which he recognized four
pink Dormin tablets. Like many cars, the Cirrus had a
storage compartment in the lower portion of the
driver’s door. In that compartment, Gambini observed a
document and a Jennings .22-caliber handgun. Further
inspection revealed that Morris’s name was on the docu-
ment.
  The search proceeded to 707 Albert’s detached garage.
There, Gambini discovered two vehicles, one being a
Lincoln Town Car. The Town Car’s trunk was ajar, and
inside Gambini found three plastic bags filled with a
total of nearly $5,000 in cash. Subsequent analysis
revealed Morris’s fingerprints on one of the bags. Using
No. 08-2979                                             5

a distinctive red key chain found inside the house,
Gambini opened the Town Car, where he found a docu-
ment from the Department of Public Aid addressed to
Lonnie Morris.
  Following the search, Detective Gambini and a colleague,
Detective Rossow, escorted Morris to jail. According to
Gambini’s testimony, Morris told the two detectives
while in transit: “This case is dropped. You had no proba-
ble cause to get in my house.”
  Morris was subsequently released. Four days later,
authorities pulled him over for driving without wearing
a seat belt. Detective Gambini came to the traffic stop,
where he observed and seized the same distinctive red
key chain that he had used to open the Town Car during
the search of 707 Albert.
  In February 2006, a federal grand jury returned an
indictment charging Morris with three offenses.
Count One alleged that Morris knowingly and intention-
ally possessed, with intent to distribute, 23.7 grams of
a substance containing heroin, thereby violating 21
U.S.C. § 841(a)(1). Count Two charged Morris, a con-
victed felon, with possessing a firearm. See 18 U.S.C.
§§ 922(g)(1), 924(e)(1). Count Three averred that Morris
had knowingly possessed a firearm in furtherance of
the drug trafficking crime alleged in Count One, a viola-
tion of 18 U.S.C. § 924(c). Morris was arrested shortly
thereafter.
  A jury trial was held in January 2007. The government
presented evidence of the preceding facts, as well as
several expert witnesses, including Sergeant Welsh, who
6                                                No. 08-2979

testified to common practices observed in the area
drug trade. The jury found Morris guilty of all three
counts contained in the indictment. The court later sen-
tenced Morris to a total of 300 months in prison. Morris
now appeals the conviction.


                         II. A NALYSIS
  Morris presents three arguments on appeal. First, he
contends that the evidence was insufficient to support
his conviction. Specifically, he argues (1) that the gov-
ernment failed to prove that he constructively possessed
either the drugs or the gun, and (2) that if he did possess
the gun, the evidence did not support the jury’s finding
that such possession was “in furtherance of” a drug
trafficking crime. Second, and relatedly, Morris asserts
that the district court erred in refusing to give a proffered
jury instruction defining the term “in furtherance of.”
Finally, Morris challenges the district court’s decision
to admit Sergeant Welsh’s expert testimony con-
cerning distributable quantities of heroin. Although we
see some merit in these challenges, none are ultimately
persuasive.


    A. Sufficiency of the Evidence
  A defendant attacking the sufficiency of the evidence
used to convict him “ ‘faces a nearly insurmountable
hurdle.’ ” United States v. Pulido, 69 F.3d 192, 205 (7th Cir.
1995) (quoting United States v. Teague, 956 F.2d 1427, 1433
(7th Cir. 1992)). To succeed, Morris must show that,
No. 08-2979                                                  7

based on the evidence presented at trial, no rational
juror could find guilt beyond a reasonable doubt. United
States v. Luster, 480 F.3d 551, 555 (7th Cir. 2007); United
States v. Hach, 162 F.3d 937, 942 (7th Cir. 1998) (“Only if
the record is devoid of evidence from which a jury
could find guilt will we reverse.”). In conducting this
analysis, we view the evidence in the light most favor-
able to the government. United States v. Richardson, 208
F.3d 626, 631 (7th Cir. 2000).
  Morris’s initial sufficiency of the evidence arguments
relate to his possession of the drugs and firearm. His
remaining challenge is that the evidence was insufficient
to find that he possessed the firearm “in furtherance of”
a drug trafficking crime.


  1. Constructive Possession
  All three counts on which the jury convicted Morris—
possessing heroin with intent to distribute, see 21 U.S.C.
§ 841(a)(1); possessing a firearm in furtherance of a drug
trafficking crime, see 18 U.S.C. § 924(c)(1)(A); and possess-
ing a firearm as a convicted felon, see id. § 922(g)(1)—
involve one common element: possession. Morris now
challenges this element with respect to each of his
three convictions.
  For each of these offenses, possession can be either
actual or constructive. See United States v. Irby, 558 F.3d
651, 654 (7th Cir. 2009) (applying § 841(a)(1)); United
States v. Castillo, 406 F.3d 806, 812 (7th Cir. 2005) (applying
§ 924(c)(1)); United States v. Caldwell, 423 F.3d 754, 757-58
8                                                No. 08-2979

(7th Cir. 2005) (applying § 922(g)(1)). Constructive posses-
sion is a legal fiction whereby an individual is deemed
to “possess” contraband items even when he does not
actually have immediate, physical control of the objects,
i.e., the individual “does not possess them in a literal
sense.” United States v. Windom, 19 F.3d 1190, 1200 (7th Cir.
1994); see also United States v. Kitchen, 57 F.3d 516, 524 n.2
(7th Cir. 1995) (defining “actual possession”). Because the
government does not contend that Morris actually pos-
sessed either the drugs or the gun, we confine our dis-
cussion to constructive possession.
  To determine constructive possession of both the drugs
and the gun, we apply the same test. See, e.g., United
States v. Kelly, 519 F.3d 355, 361 (7th Cir. 2008). Compare
Irby, 558 F.3d at 654 (requiring proof of “owner-
ship, dominion, or control” to demonstrate constructive
possession of drugs), with Caldwell, 423 F.3d at 758 (requir-
ing that a person “ha[ve] the power . . . to exercise domin-
ion and control” over a gun). In either case, the govern-
ment must prove a nexus between the defendant and
the relevant item to separate true possessors from mere
bystanders. Richardson, 208 F.3d at 632. Proximity to the
item, presence on the property where the item is located,
or association with a person in actual possession of the
item, without more, is not enough to support a finding
of constructive possession. Windom, 19 F.3d at 1200
(citing United States v. DiNovo, 523 F.2d 197, 201 (7th Cir.
1975)). Instead, the defendant must exercise dominion
and control over the item. Irby, 558 F.3d at 654; Kelly, 519
F.3d at 361. The government may prove constructive
possession through direct as well as circumstantial evi-
dence. Kelly, 519 F.3d at 361.
No. 08-2979                                              9

  We turn first to the question of whether Morris con-
structively possessed the heroin found in the basement
at 707 Albert. We then consider whether Morris construc-
tively possessed the heroin and the pistol found in the
door of the Chrysler Cirrus.


 a.   Constructive Possession of the Heroin in 707 Albert’s
      Basement
   Upon executing the search warrant at 707 Albert, author-
ities discovered 23.6 grams of heroin in the basement.
Morris argues that the evidence was insufficient to
prove the requisite nexus connecting him to these drugs.
Such a nexus is typically shown in one of two ways.
First, if the government demonstrates that the defendant
had “exclusive control” over the property where the
drugs were discovered, one may infer that the defen-
dant constructively possessed the items, including drugs,
found on that property. Castillo, 406 F.3d at 812. In
this case, however, the government did not rest its argu-
ments at trial on whether Morris possessed such control.
Instead, the government focused on the second means
of proving a nexus between Morris and the drugs in the
basement: substantial connection.
  In the absence of exclusive control, evidence that a
defendant had a “substantial connection” to the location
where contraband was seized is sufficient to establish
the nexus between that person and the drugs. See Richard-
son, 208 F.3d at 632; see also United States v. Brown, 328
F.3d 352, 355 (7th Cir. 2003). As we will discuss, we have
found a substantial connection in a variety of circum-
10                                            No. 08-2979

stances, and we conclude that such a connection existed
here.
  In Richardson, 208 F.3d 626, for example, we found the
defendant to be substantially connected to a residence
when he kept clothes and medicine at the house,
received mail there, and “admitted that he was the care-
taker and landlord of the address.” Id. at 632. Similarly,
in Kitchen, 57 F.3d 516, we held that the jury was right
to find constructive possession when the defendant
had received calls at the home where weapons were
found, had stated that he lived at that address, and had
been seen at the address on numerous occasions. Id. at
520. In addition, investigators located the defendant’s
clothing, jewelry, and mail at the residence. Id. Finally,
the defendant had spent substantial amounts of money
repairing the house. Id.
  The facts of the instant case are not as straightforward
as those in Richardson and Kitchen. During the search of
707 Albert, the police did not recover any tangible
items linking Morris to the premises. They found no
clothing, no personal items, and no mail sent to Morris
at that address. Morris claims that the government’s case
was founded on mere proximity alone and that the
absence of tangible evidence linking him to 707 Albert
is determinative. In support, Morris relies principally
on two cases, Windom, 19 F.3d 1190, and United States v.
Herrera, 757 F.2d 144 (7th Cir. 1985).
  In Windom, the government produced no evidence
linking the defendant to drugs found in a backpack
that was recovered from a house belonging to the defen-
No. 08-2979                                               11

dant’s niece. 19 F.3d at 1201. The defendant was in the
house when the backpack was discovered, but the court
held that his presence alone was not enough to support
the jury’s conviction. Id. at 1200-01.
  We reached the same conclusion in Herrera. There, the
defendant was arrested after he left a house carrying a
brown bag that contained heroin. 757 F.2d at 147. A
search of the house he was leaving revealed a locked
footlocker containing numerous packages of heroin, a
gun, money, a scale, and plastic bags. Id. The district court
convicted the defendant of possessing the heroin found
in the footlocker. Id. at 148. On appeal, we overturned
the conviction related to these drugs, concluding that
the government had not shown that the defendant had
the ability to exercise dominion and control over them.
Id. at 150. The footlocker was locked, the defendant had
no key, and the purity of the heroin seized on the defen-
dant’s person did not match the purity of the heroin
found inside the locker. Id. The only evidence of the
defendant’s “possession” of the drugs in the footlocker
was his presence on the property where it was located,
and that was insufficient. Id.
  We agree with Morris that his case bears some semblance
to Windom and Herrera. There is a dearth of tangible
evidence linking Morris to 707 Albert, and we recognize
that much of the government’s case at trial rested on
Morris’s proximity to the drugs in the basement. As
we mentioned, however, the government may use cir-
cumstantial evidence to demonstrate the substantial
connection sufficient to prove constructive possession.
12                                             No. 08-2979

Kelly, 519 F.3d at 361. And, although proximity alone
is not enough to establish constructive possession, the
requisite additional evidence, circumstantial though it
may be, need not take the form of physical, tangible
items that link an individual to a given location.
  The D.C. Circuit, in words that we find persuasive, has
said that “proximity coupled with evidence of some
other factor—including connection with [an impermissible
item], proof of motive, a gesture implying control, evasive
conduct, or a statement indicating involvement in an
enterprise is enough to sustain a guilty verdict.” United
States v. Richardson, 161 F.3d 728, 732 (D.C. Cir. 1998)
(quotations omitted); see also United States v. Gibbs, 904
F.2d 52, 57 (D.C. Cir. 1990). We find that there was
ample evidence of these “other factors.”
  We begin with Morris’s flight from the basement. We
have previously identified a defendant’s flight as the
“something more” sufficient to overcome the mere pres-
ence doctrine. See United States v. Starks, 309 F.3d 1017,
1025 (7th Cir. 2002). In Starks, police raided a house
and discovered the two defendants in a room with a table
full of drugs. Id. at 1019. The men fled, hiding in a
closet. Id. at 1020. The house itself was largely devoid of
possessions, resulting in no tangible evidence to link the
defendants to the house. Id. The defense argued on
appeal that mere presence was insufficient to support a
finding of possession by one of the defendants. Id. at
1022. In upholding the conviction, we identified the de-
fendant’s flight as one factor supporting the jury’s
verdict. Id. at 1025 (“From the very infancy of criminal
No. 08-2979                                                    13

litigation, juries have been permitted to consider flight
as evidence of consciousness of guilt and thus of guilt
itself.” (quotations omitted)). In the present case, the
inference of guilt drawn from Morris’s flight is only
strengthened when the area from where he was fleeing
contained nothing of any substance but the drugs and
accompanying paraphernalia.1
  Morris’s flight was not the only circumstantial evidence
of his “substantial connection” to 707 Albert. His own
words provided more. Morris made two statements
indicating a connection with the house. First, following
his arrest, Morris told Detective Gambini: “This case is
dropped. You had no probable cause to get in my
house” (emphasis added). Next, according to a written
statement provided by Donte Webb, one of Morris’s
cousins, Morris told Webb “that the police had raided one
of [Morris’s] houses.” Such statements certainly give rise
to the inference that Morris was substantially connected
to 707 Albert. See Starks, 309 F.3d at 1024 (discussing that
a “link” distinguishing mere presence from participa-
tion could include “the giving of incriminating state-
ments”); cf. Richardson, 208 F.3d at 632 (denying a
sufficiency-of-the-evidence challenge in part because


1
  As previously noted, the contents of the basement included a
mattress leaned against one wall, behind which police located
the bag of heroin; a washer and dryer; a cellular telephone; a
razor blade; a digital scale; some small plastic bags; and debris.
Only the washer and dryer would seem to have any legitimate
purpose, and we doubt very much that Morris was doing
laundry.
14                                               No. 08-2979

the defendant admitted to being the landlord of the
property); Richardson, 161 F.3d at 732 (indicating that a
statement intimating involvement would be enough to
support a conviction); Kitchen, 57 F.3d at 520 (denying a
sufficiency-of-the-evidence challenge in part because
the defendant admitted to living at the address).
  Other evidence supporting the jury’s finding of the
requisite connection between Morris and 707 Albert
included the frequency of Morris’s presence at the
house during previous weeks, see Kitchen, 57 F.3d at 520
(noting that the defendant had been seen at the house
“on numerous occasions”), and the Lincoln Town Car
parked in the house’s garage, which contained a docu-
ment addressed to Morris and whose key Morris
possessed during the traffic stop four days after the
search. In addition, police recovered his fingerprint on
the money bag that was found in the Town Car. Also, in
a search of 707 Albert’s garbage, police discovered mail
to Morris, albeit not sent to that address.
  In sum, although the evidence might not have been
as persuasive as Morris’s name on the lease, his clothes
in the closet, or his letters in the mailbox, it provided
sufficient circumstantial support for the jury’s finding
that Morris had a substantial connection to 707 Albert.
This connection gave rise to the permissible inference
that Morris constructively possessed the drugs contained
in its basement. See Starks, 309 F.3d at 1021-22 (“[T]he trier
of fact is entitled to employ common sense in making
reasonable inferences from circumstantial evidence.”).
Thus, we reject Morris’s challenge to the sufficiency of the
No. 08-2979                                                 15

evidence related to the 23.6 grams of heroin found in 707
Albert, and we turn to the sufficiency of the evidence
pertaining to the drugs and firearm found in the
Chrysler Cirrus parked in the driveway.


  b.   Constructive Possession of the Heroin and Firearm in the
       Cirrus
  The search warrant executed at 707 Albert also autho-
rized the search of two vehicles, one of which was the
Chrysler Cirrus that Morris drove to the house the day
of the raid. From storage areas in the Cirrus’s driver’s-side
door, police recovered two small bags of “an off-white
powdery substance,” later identified as 0.09 grams of a
mixture containing heroin; a handgun; and a document
with Morris’s name on it. Again, because the govern-
ment does not claim that Morris was ever seen
handling either the drugs or the gun, Morris challenges
the sufficiency of the evidence demonstrating that he
constructively possessed the items found in the car.
We find this to be a much simpler question than Morris’s
initial challenge concerning the drugs in 707 Albert’s
basement.
  Morris’s arguments again rest on the mere presence
doctrine. The car was registered in another person’s
name, and there was evidence that other people drove
the vehicle during the days and weeks preceding the
search on June 2. Morris’s fingerprints were found on
neither the firearm nor the bags containing the drugs.
That, however, is where the evidence favorable to
Morris ends.
16                                             No. 08-2979

  Detective Gambini testified that he had seen Morris
driving the Cirrus on multiple occasions during his
surveillance of 707 Albert. On June 2, the day of the raid,
Gambini observed Morris in the Cirrus near the house.
As Gambini watched, Morris engaged in three separate
exchanges with individuals approaching the car, the
third of which occurred in 707 Albert’s driveway. After
the final exchange, Morris exited the car and entered 707
Albert, which authorities raided shortly thereafter.
Gambini testified that no one else accessed the car in
the interim.
  This evidence is sufficient to sustain the jury’s finding
that Morris constructively possessed both the drugs
and the firearm found in the Cirrus. Although Gambini
did not see what Morris exchanged with his three
visitors, it was reasonable for the jury to conclude, par-
ticularly given the drugs, the gun, and the document in
Morris’s name later found in the car, that Gambini wit-
nessed three drug transactions. See Brown, 328 F.3d at 355
(noting that authorities “need not catch a defendant red-
handed to satisfy the possession requirement”); Starks,
309 F.3d at 1021-22 (commenting that juries may use
common sense to reach reasonable inferences from cir-
cumstantial evidence). That Morris was dealing drugs
from the Cirrus and possessed the drugs and gun found
in the car is certainly a reasonable inference jurors could
draw from these facts.
  This case bears notable similarity to United States v.
Garrett, 903 F.2d 1105 (7th Cir. 1990), where we upheld a
conviction on a firearms charge when police appre-
No. 08-2979                                                   17

hended a man who was suspected of soliciting a prostitute.
Id. at 1107, 1110. The man was arrested just before he
entered a vehicle that contained both drugs and a gun;
neither the car nor the gun was registered to the defen-
dant. Id. at 1107-08. That the defendant had keys to the car,
and that the gun and drugs were on the floor of the
driver’s side, were facts sufficient to support the convic-
tion. Id. at 1110-12; cf. United States v. Moralez, 964 F.2d 677,
680 (7th Cir. 1992) (finding facts “even more incriminating
than [those] in Garrett” when the defendant, who was
apprehended driving a car containing nearly thirty pounds
of marijuana, was “in complete control and possession of
the vehicle”).
  Here, where Morris was seen driving the vehicle on
multiple occasions in the days prior to the raid, where
he was seen conducting probable drug transactions from
the car on the day of the raid, and where he was the
vehicle’s last known driver, the evidence was sufficient
to find that he constructively possessed the heroin and
the firearm found in the storage compartments of the
car’s door. Given these circumstances, that the car
was not registered in Morris’s name, that other people
occasionally had access to the vehicle, and that there
were no fingerprints found on the drugs or the gun do
nothing to change that conclusion.


  2.   Possessing a Firearm “in Furtherance of” a Drug Traffick-
       ing Crime
  Having concluded that Morris constructively possessed
the firearm and the drugs, it is a small step, given the
18                                             No. 08-2979

facts, to link the two together and conclude that there
was ample evidence to convict Morris of possessing that
firearm in furtherance of a drug trafficking crime. See
18 U.S.C. § 924(c)(1)(A).
  Morris argues that the evidence failed to establish a
“specific nexus between the particular weapon and the
particular drug crime at issue,” quoting Castillo, 406 F.3d
at 815. Such a nexus is certainly required, but we fail to
see what additional evidence the government could have
shown short of Morris having had the gun on his person—
which, as we have made clear, is not necessary. See id.
at 812 (noting that a § 924(c) violation can be shown
through either actual or constructive possession).
  To address Morris’s claim, we first reiterate the “par-
ticular drug crime” that the jury found “furthered” by
his possession of the firearm. It was described in Count
One of the indictment, which alleged possession, with
intent to distribute, 23.7 grams of heroin. This
amount encompassed both the 23.6 grams of heroin
authorities found in 707 Albert and the 0.09 grams of
heroin recovered from the Cirrus.
  Morris attempts to distinguish between the drugs found
in the car and those found in the house. In his eyes, the
small amount of heroin from the car was not enough to
imply any intent to distribute, only to use. The gun,
therefore, which the government could link only to that
smaller quantity, was not furthering any drug trafficking
activity whatsoever.
  But Morris’s argument misses the mark. It is true that
0.09 grams is well below the quantities that the govern-
No. 08-2979                                               19

ment’s expert testified would generally be considered
a distributable amount. But such testimony is meant
only as a guideline; it is incontrovertible that any amount
is “distributable” when, as here, there is circumstantial
evidence that the quantity of drugs, no matter how
small, was in fact intended for distribution. That is what
the jury must have concluded in this case—a reasonable
conclusion given that police had just observed Morris
engage in three probable drug transactions and later
found additional drugs, packaged for resale, in the car
from which those transactions occurred.
  Furthermore, as we just noted, the indictment, which
charged Morris with the total amount of heroin dis-
covered from both the house and the car, made no dis-
tinction between the two locations where the drugs were
located. Implicit in the jury’s guilty verdict on Count One
was its finding that Morris possessed the quantity of
heroin specified therein—which included the 0.09 grams
from the car—for distribution, not personal use. Cf.
United States v. Luciano, 329 F.3d 1, 6 (1st Cir. 2003) (con-
cluding that a jury “inescapably found” that the
defendant possessed heroin discovered both on his
person and inside his house when the jury’s findings as
to quantity mathematically mandated such a conclu-
sion); Castillo, 406 F.3d at 818 (discussing Luciano). Thus,
the “particular drug crime” involved both the drugs
from the car and the house, and the statute requires
only that the firearm be linked to this crime, not that it
be linked to all, or any particular subset of, the under-
lying drugs. See 18 U.S.C. § 924(c)(1)(A).
20                                                No. 08-2979

  We turn, then, to the evidence tying the gun to that
crime. It was substantial. To begin, the government’s
expert, Sergeant Marc Welsh, testified that firearms
were commonly used by drug dealers for protection from
both police and other dealers.2 The evidence presented
comported with Welsh’s testimony. The gun, partially
concealed by a document bearing Morris’s name, was
in the driver’s door. Morris was the driver. Police watched
Morris engage in three exchanges that the jury could
reasonably have concluded were drug transactions, the
last of which occurred in 707 Albert’s driveway, where
Morris parked and exited the car. Searches of the house
where the car was parked and the car itself revealed
23.6 and 0.09 grams of heroin, respectively. It was entirely
reasonable for the jury to conclude that Morris possessed
the gun to protect either himself, his drugs, or his
money while he trafficked the drugs in the car and the
house.
  Our case law, bolstered by cases from our sister circuits,
leaves no room to question the jury’s conclusion under
such facts. See United States v. Seymour, 519 F.3d 700, 715
(7th Cir. 2008) (listing factors useful in analyzing the “in
furtherance of” question, including the type of drug
activity being conducted, the firearm’s accessibility
and proximity to the drugs, and the circumstances under
which the firearm was found); Castillo, 406 F.3d at 815



2
  Sergeant Welsh served as both an investigator and a wit-
ness in this case. Below, we address the potential implications
of Welsh’s dual role. See infra, pt. II.C.
No. 08-2979                                              21

(giving as an example of the required nexus “that the
specific weapon at issue . . . [was] available for the pro-
tection of the drug dealer or his drugs”); United States v.
Gaston, 357 F.3d 77, 83 (D.C. Cir. 2004) (concluding that
weapons were possessed “in furtherance of” when they
were “strategically located” for quick and easy accessibil-
ity); Luciano, 329 F.3d at 3-4, 6 (upholding an “in further-
ance of” conviction when the defendant was caught
dealing drugs outside his apartment but firearms and
additional drugs were found inside the apartment).
  Having reached the end of Morris’s arguments
relating to the sufficiency of the evidence, we turn to his
remaining claims, beginning with his challenge to the
court’s decision not to instruct the jury on the meaning
of “in furtherance of.”


  B. “In Furtherance Of” Instruction
  During the instructions conference, Morris’s counsel
offered the following instruction pertaining to Count Two
of the indictment, which charged Morris with possessing
a firearm “in furtherance of” a drug trafficking crime,
in violation of 18 U.S.C. § 924(c)(1)(A):
    The phrase “in furtherance of” as used in these
    instructions means to advance or promote the
    commission of the underlying drug trafficking
    offense. The government must prove a specific
    nexus between the firearm and the crime charged.
  After some discussion, and over defense counsel’s
objection, the court declined to give the instruction.
22                                               No. 08-2979

We review the district court’s refusal to give a jury in-
struction for an abuse of discretion. United States v. Muham-
mad, 502 F.3d 646, 655 (7th Cir. 2007).
  The problem with Morris’s argument is that it rests
on the faulty premise that “in furtherance of” requires
definition. In Castillo, 406 F.3d 806, we noted that “an
instructive line of cases holds that it is not error—plain
or otherwise—to fail to give a definition of a statutory
term or phrase that carries its natural meaning and that
meaning is accessible to lay jurors.” Id. at 821. Other
cases have alluded to this same principle. Cf. United
States v. Santos, 932 F.2d 244, 252 (3d Cir. 1991) (finding
no plain error when the district court declined to define
“preponderance of the evidence” because, in part, the
phrase’s legal meaning was consistent with its common
meaning); United States v. Sherwood, 770 F.2d 650, 654
(7th Cir. 1985) (finding no plain error when the district
court declined to define “willfully” because the
ordinary meaning of the term likely did not confuse
the jury).
   In Castillo, we discussed “in furtherance of” at length,
commenting on the phrase’s “natural meaning,” 406
F.3d at 814 (“furthering, advancing or helping forward”
(quotations omitted)), and stating that it “means what
it says,” id. at 815; see also id. at 821 (“ ‘[I]n furtherance
of’ naturally and necessarily connotes more than mere
presence or innocent possession.” (first emphasis added)).
Thus, although the court was free to give an instruc-
tion defining “in furtherance of,” we determined that it
was not error to decline to do so. Id. at 821-22.
No. 08-2979                                                  23

  In an attempt to minimize Castillo’s weight, Morris
notes, correctly, that the discussion regarding the plain
meaning of “in furtherance of” was not the core holding
of the case. Indeed, by our count, the phrase’s plain
meaning was one of three reasons we provided to
support our conclusion that the district court did not
plainly err in refusing to define “in furtherance of.” Id. at
820-21. But that fact does nothing to detract from the
import of our comments, which was that the phrase
carries a readily understood meaning that jurors compre-
hend without additional definition.
  Further, the facts of Castillo are closer to those now
before us than Morris would have us believe. A second
factor we found important in our “in furtherance of”
discussion was the comments made by the attorneys
during closing arguments. Id. There, the prosecutor said
the following: “So how did that shotgun further a drug
crime? That’s the question. Did it further—simply did it
help the drug crime? Did it aid a drug crime in some way?
How did that shotgun help this defendant possess with
intent to distribute narcotics?” Id. at 820.
  Here, the prosecutor did not use words like “help” or
“aid.” But taken in context, his comments left little
doubt about the meaning of “in furtherance of”:
    [W]hat furthers the crime of drug trafficking.
    Protection of your product, protection of your
    proceeds, protection of your person. . . . It’s impor-
    tant for drug dealers to protect themselves, first
    and foremost, and almost as importantly their
    product and their cash, and that’s exactly what
24                                             No. 08-2979

     happened here. The defendant had the gun in the
     driver’s side door just below the drugs that he
     was selling, protecting that product, protecting
     his person, and he was using guns to protect the
     money that he was generating from the heroin
     sales.
  We conclude that the district court did not err by refus-
ing to include a jury instruction defining the phrase “in
furtherance of,” as used in 18 U.S.C. § 924(c)(1)(A).
The words have a plain meaning that is easily under-
stood by jurors, rendering any definitional instruction
perhaps helpful but not necessary. This conclusion is
bolstered by the prosecutor’s comments during closing
arguments, which, to the extent further illumination
might have been desired, provided additional light.


 C. Admission of Sergeant Welsh’s Expert Testimony
  Morris’s final argument is that the district court
should not have admitted testimony by Sergeant Marc
Welsh, who testified as an expert for the government. The
government offered Welsh’s testimony to explain com-
mon practices of street-level narcotics sales, including
what quantities of drugs are generally possessed
for purposes of distribution rather than individual con-
sumption. Welsh testified that 23.7 grams of heroin
“would be consistent with distribution quantity.”
  The rub, however, is that Welsh was also the supervisor
of the MNU at the time the unit raided 707 Albert. Testi-
mony by other members of the search team and by
No. 08-2979                                                25

Welsh himself on cross-examination made it clear that
Welsh was personally involved in executing the warrant
on the house. Morris claims that Welsh’s dual role—as both
investigator and expert witness—caused his testimony to
run afoul of the Federal Rules of Evidence, particularly
Rules 704(b) and 403. We disagree.
  Government prosecutors often call expert witnesses to
discuss common practices employed by drug dealers.
See United States v. Foster, 939 F.2d 445, 451 & n.6 (7th
Cir. 1991) (collecting cases and noting that our circuit
“is quite familiar with the use during trial of expert
testimony as to the methods used by drug dealers”);
see also United States v. Anderson, 61 F.3d 1290, 1297 (7th
Cir. 1995). We have upheld the practice in a number of
contexts related to the narcotics trade. See United States
v. Upton, 512 F.3d 394, 401 (7th Cir. 2008) (discussing
various contexts); see also, e.g., United States v. Gonzalez,
933 F.2d 417, 428-29 (7th Cir. 1991) (use of short phone
calls to avoid detection); United States v. Solis, 923 F.2d
548, 551 (7th Cir. 1991) (use of beepers); United States v.
Rollins, 862 F.2d 1282, 1292 (7th Cir. 1988) (use of
narcotics code words).
  For many drug crimes, the government bears the
burden of proving that the defendant possessed a given
state of mind—often, as here, the intent to distribute
narcotics. See 21 U.S.C. § 841(a)(1). But it is usually diffi-
cult or impossible to provide direct evidence of a defen-
dant’s mental state. Cf. Pavlick v. Mifflin, 90 F.3d 205, 209
(7th Cir. 1996) (“Direct evidence of knowledge is diffi-
cult—sometimes impossible—to obtain; therefore the
26                                                 No. 08-2979

Supreme Court has held that [a defendant’s mental state]
need not be proven by direct evidence.”). Instead, an
individual’s intent is generally proven through circumstan-
tial evidence, often in the form of expert testimony. See,
e.g., United States v. Lipscomb, 14 F.3d 1236, 1239-43 (7th Cir.
1994) (examining in depth the role of expert testimony
by law enforcement officers as circumstantial evidence
of an individual’s intent); Solis, 923 F.2d at 551 (finding
expert testimony helpful “to establish . . . intent through
circumstantial evidence”); cf. Pavlick, 90 F.3d at 209
(“Whether a [defendant acted with a requisite mental
state] is a question of fact subject to demonstration in the
usual ways, including inference from circumstantial
evidence.” (quotations omitted)). As we have explained,
experts “simply describe[] in general terms the
common practices of those [hypothetical individuals]
who clearly do possess the requisite intent, leaving un-
stated the inference that the defendant, having been
caught engaging in more or less the same practices, also
possessed the requisite intent.” Lipscomb, 14 F.3d at 1239.
The jury is then left to decide whether to make the
logical connection from the expert’s testimony to the case
at hand.
  In offering expert testimony as circumstantial evidence
of a defendant’s intent, however, courts must be wary that
the expert witness not cross into the jury’s realm or
otherwise risk prejudicing the jury. See Fed. R. Evid. 704(b),
403. Morris contends Welsh’s testimony did both.
  Rule 704 governs opinions that witnesses offer on so-
called “ultimate issues.” The rule is divided into two
No. 08-2979                                                    27

parts, a general rule and an exception. The general rule
states that “testimony in the form of an opinion or infer-
ence otherwise admissible is not objectionable because it
embraces an ultimate issue to be decided by the trier of
fact.” Fed. R. Evid. 704(a). The exception provides as
follows:
    No expert witness testifying with respect to the
    mental state or condition of a defendant in a
    criminal case may state an opinion or inference
    as to whether the defendant did or did not have
    the mental state or condition constituting an
    element of the crime charged or of a defense
    thereto. Such ultimate issues are matters for the
    trier of fact alone.
Id. 704(b).3
  Under the rule, the potential problem arises when
experts stray from their analysis of detached facts and offer
opinions regarding the defendant’s actual mental state;
such conclusions are meant to be the exclusive province
of the jury. It must be clear from the expert’s testi-
mony that he “was merely identifying an inference that
might be drawn from the circumstances surrounding the
defendant’s arrest, and was not purporting to express
an opinion as to the defendant’s actual mental state.”
Lipscomb, 14 F.3d at 1240 (quotations omitted).


3
  In Lipscomb, we questioned the applicability of Rule 704(b)
to non-medical experts but ultimately acknowledged that the
rule limits the expert testimony of law enforcement officials
as well. 14 F.3d at 1242; see also United States v. Mancillas, 183
F.3d 682, 706 (7th Cir. 1999).
28                                              No. 08-2979

  Rule 403, meanwhile, permits a court to exclude
evidence “if its probative value is substantially out-
weighed by the danger of unfair prejudice.” Testimony
runs the risk of being overly prejudicial when, as here,
the expert witness was a law enforcement officer who
was also involved in the investigation at issue. See Upton,
512 F.3d at 401; Lipscomb, 14 F.3d at 1242; see also United
States v. Alvarez, 837 F.2d 1024, 1030 (11th Cir. 1988)
(discussing the “serious risk of undue prejudice” that
arises from a government agent testifying as an expert);
United States v. Brown, 776 F.2d 397, 401 n.6 (2d Cir. 1985)
(noting that the risk of prejudice is increased when the
expert opinion “is given by the very officers who were
in charge of the investigation” (quotations omitted)). The
danger is “that the jury may attach undue weight to
the officer’s testimony, either by mistaking an expert
opinion for what is really only an eyewitness observa-
tion, or by inferring that the officer’s opinion about the
criminal nature of the defendant’s activity is based on
knowledge of the defendant beyond the evidence at
trial.” Lipscomb, 14 F.3d at 1242 (quotations omitted).
  We find that the content and context of Sergeant
Welsh’s testimony avoided the potential pitfalls contem-
plated by Rules 704 and 403. Perhaps most importantly,
Welsh testified only as an expert. This is a marked differ-
ence from previous cases dealing with this issue, where
the relevant witness took the stand as both a lay witness
and an expert. See, e.g., Upton, 512 F.3d at 398; United
States v. Mansoori, 304 F.3d 635, 653 (7th Cir. 2002);
Lipscomb, 14 F.3d at 1238; United States v. de Soto, 885
F.2d 354, 360 (7th Cir. 1989).
No. 08-2979                                              29

  Here, the government produced numerous members
of the Metro Narcotics Unit who testified to the events of
June 2, 2005, the day of the raid on 707 Albert. Sergeant
Welsh was not one of them. Instead, Welsh’s testimony
focused exclusively on his expert opinions regarding the
drug trade in Rockford and his analysis of the facts
related to Morris’s case, e.g., that 23.7 grams of heroin,
possessed by anyone, “would be consistent with distribu-
tion quantity.” Never once did Welsh refer to Lonnie
Morris specifically or even allude to his impressions or
recollections from the day of the search, nor did he
express an opinion about Morris’s actual state of mind. See
Mancillas, 183 F.3d at 706 (concluding that a dual-role
witness “based his opinion on his knowledge of the
drug trade rather than on any alleged or conceived famil-
iarity with the working of [the defendant’s] mind”);
Lipscomb, 14 F.3d at 1243.
  This is not to say that the jury was unaware of Welsh’s
role in the Morris investigation. Several government
witnesses referred to Sergeant Welsh during their testi-
mony, and Welsh acknowledged on the stand that he
was the supervisor of the MNU and had been involved
in the search of 707 Albert. Notably, however, virtually
all of Welsh’s statements regarding his role in the investi-
gation were not brought out by the government but
rather were elicited by defense counsel on cross-exam-
ination.
  The government’s decision not to use Welsh as a fact
witness was an important step in avoiding potential
juror confusion or crossing the line into improper opinion.
30                                            No. 08-2979

See Mansoori, 304 F.3d at 654 (recognizing a reduced
potential for prejudice where the government structures
testimony “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”).
  In addition, the district court gave a standard instruc-
tion to the jury, reminding it of the following:
     You should judge [expert] testimony in the same
     way that you judge the testimony of any other
     witness. The fact that such a person has given an
     opinion does not mean you’re required to accept
     it. Give the testimony whatever weight you think
     it deserves considering the reasons given for the
     opinion, the witness’ qualifications, and all the
     other evidence in the case.
We have found the use of similar instructions to be an-
other factor mitigating against jury confusion. See, e.g.,
id. (finding it helpful when the jury was instructed that
“the fact an expert has given an opinion does not mean
that it is binding upon you or that you are obligated to
accept the expert’s opinion as to the facts”).
  Given these facts, we conclude that the district court
did not admit Sergeant Welsh’s testimony in violation of
Rule 704(b) because it was made clear “in the nature of
the examination[] that the opinion [was] based on the
expert’s knowledge of common criminal practices, and
not on some special knowledge of the defendant’s
mental processes.” Lipscomb, 14 F.3d at 1242. For the same
reasons, Welsh’s testimony was not unfairly prejudicial
and did not violate Rule 403.
No. 08-2979                                              31

                    III. C ONCLUSION
  First, there was sufficient evidence to sustain Morris’s
conviction on the three counts contained in the indict-
ment. Second, the district court did not err by refusing to
define the phrase “in furtherance of” in its instructions to
the jury. Finally, the court properly admitted the expert
testimony of Sergeant Welsh. We A FFIRM Morris’s con-
viction.




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