AMENDED OPINION
    UNPUBLISHED
 
    UNITED STATES COURT OF APPEALS

    FOR THE FOURTH CIRCUIT

    UNITED STATES OF AMERICA,
    Plaintiff-Appellee,
 
    v.                                                                     No. 98-4272
 
    PETER ROLLACK,
    Defendant-Appellant.
 
    Appeal from the United States District Court
    for the Western District of North Carolina, at Charlotte.
    Graham C. Mullen, Chief District Judge.
    (CR-96-168)
 
    Argued: December 3, 1998

    Decided: March 1, 1999

    Amended Opinion Filed: May 2, 2014
 
    Before ERVIN and HAMILTON, Circuit Judges, and HILTON,
    Chief United States District Judge for the Eastern District of
    Virginia, sitting by designation.
 
 
 
    Affirmed by unpublished opinion. Chief Judge Hilton wrote the opin-
    ion, in which Judge Ervin and Judge Hamilton joined.
 
 
 
    COUNSEL
 
    ARGUED: Christopher Cary Fialko, Charlotte, North Carolina, for
    Appellant. Gretchen C.F. Shappert, Assistant United States Attorney,
    Charlotte, North Carolina, for Appellee. ON BRIEF: Mark T. Cal-
    loway, United States Attorney, Charlotte, North Carolina, for Appel-
    lee.
    Unpublished opinions are not binding precedent in this circuit. See
    Local Rule 36(c).
 
 
 
    OPINION
 
    HILTON, Chief District Judge:
 
    On January 9, 1998 Peter Rollack (a.k.a. "Pistol Pete") was found
    guilty, by a jury, of conspiracy to possess with intent to distribute a
    quantity of cocaine and cocaine base in violation of 21 U.S.C.
    §§ 841(a)(1) and 846 (West 1981 & Supp. 1998), and knowingly
    using and carrying a firearm, and aiding and abetting such conduct,
    in relation to a drug trafficking crime, in violation of 18 U.S.C.
    § 924(c) and 2 (West Supp. 1998). Rollack now appeals his convic-
    tions. Finding no merit in the seven claims raised on appeal, we
    affirm.
 
    In the early 1990s, Conspirator 1 [the names of Rollack's co-conspirators
    and associates have been redacted] became associated with Rollack in the
    Bronx, New York. Rollack was the leader of a gang known as Sex, Money
    and Murder ("SMM"), an affiliate of the Bloods. The Bloods is a national
    gang with affiliates in many cities. SMM was engaged in distributing cocaine
    and crack cocaine. Conspirator 1 joined this gang. During that same time
    period, Conspirator 1 was involved in cocaine and crack cocaine
    distribution in Pittsburgh, Pennsylvania.
 
    Rollack began accompanying Conspirator 1 on the trips to Pittsburgh in late
    1993 and 1994. Together, they were transporting eight to ten kilo-
    grams of cocaine powder and crack cocaine at a time. Rollack served
    as a "lookout" on the trips to Pittsburgh and was paid $3,000 to
    $5,000 per trip.
 
    In 1994, Conspirator 1 and Conspirator 2 (who was named as an
    unindicted co-conspirator in the indictment against Rollack) met in
    the Bronx, and Conspirator 2 pitched Conspirator 1 about the
    potential for distributing drugs in North Carolina. As a result of this
    conversation, Conspirator 1, Rollack and several of their associates
    began making trips to North Carolina in a leased Nissan Quest van
    carrying drugs.
 
                         2
    On the second trip, Conspirator 1, Rollack and Conspirator 2 met in
    New York and drove the van, containing six to eight kilograms of
    cocaine, to North Carolina. During this trip the men sold cocaine in
    Rockingham and Lumberton, North Carolina, as well as somewhere in
    South Carolina. They then drove to Charlotte, North Carolina, where
    Conspirator 1 and Rollack were introduced by Conspirator 2 to
    Conspirator 3. Conspirator 2, Conspirator 3, Conspirator 1 and Rollack
    discussed opening crack houses in Charlotte and developing customers
    for their drug business. During this trip, they also examined several
    Charlotte neighborhoods as possible locations for their drug business.
 
    After this trip, Conspirator 1, Rollack and Conspirator 2 decided to
    return to New York temporarily. They left the van at the airport and
    flew to New York for a few days. At the time, the van contained
    approximately $70,000 and two kilograms of cocaine. Conspirator 1
    then flew down to pick up the van in order to return it to New York.
 
    The third and final trip to North Carolina also began in New York.
    Conspirator 1, Conspirator 2, Rollack, and a fourth associate left New
    York in the leased van. The van had Pennsylvania license plates, and
    contained approximately eight to ten kilograms of cocaine powder and
    crack cocaine. In Pittsburgh, they collected money and delivered
    approximately six kilograms of cocaine. The price of each kilogram
    was between $20,000 and $22,000. A portion of the drugs they
    distributed in Pittsburgh were Conspirator 1's, while the rest were
    Rollack's. From Pittsburgh, they drove to Lumberton to collect money
    on a drug debt, and then to South Carolina to collect more drug money
    and deliver more drugs. From there, they drove to Rockingham to
    meet with a customer of theirs, Conspirator 4.
 
    In Rockingham they met with Conspirator 4, who owed them between
    $80,000 to $90,000 for cocaine he had previously received. However,
    Conspirator 4 was unable to pay the full amount owed. Rollack was
    very upset about this development. While tapping a gun against his
    own head, Rollack told Conspirator 1 and Conspirator 2, "Yo, I'm
    going in there and murder him." In response to Conspirator 2's pleas,
    Rollack agreed that Conspirator 4 would have one more day to come
    up with the remaining money owed. As the four men had plans to
    drive to Charlotte for the evening, they agreed to meet with
    Conspirator 4 when they returned the next day.
 
                        3
    From Rockingham, the four men drove to Charlotte for a concert.
    They still had two kilograms of cocaine in the van and several fire-
    arms for protection. After the concert, they dropped off an associate
    in Lumberton, drove to Wilmington, North Carolina to deliver more
    cocaine, and then returned to Rockingham the next day to meet with
    Conspirator 4.
 
    When they returned to Rockingham on October 21, 1994, Conspirator
    2 paged Conspirator 4 in order to make arrangements as to where the
    men would meet. It was agreed that they'd meet in a local fast food
    restaurant. However, Conspirator 4 never arrived. Unbeknownst to
    Rollack, Conspirator 2 had phoned Conspirator 4 and warned him that
    Rollack intended to murder him. Conspirator 2 then urged Rollack and
    Conspirator 1 to leave Rockingham, because Conspirator 4 was not
    likely to arrive and pay his drug debt. Rollack refused: "Ain't nobody
    going to live in this world who owe me money." Rollack insisted that
    they drive over to Conspirator 4's house "because I'm going to murder
    his wife and kids. I ain't playing." While the three men were
    considering what to do next, law enforcement officers appeared and
    detained Conspirator 1, Conspirator 2 and Rollack. The officers had
    been tipped by an informant that drugs were being transported into
    Richmond County, North Carolina in a burgundy Nissan Quest
    bearing Pennsylvania license plates and occupied by three
    individuals. It was this tip which led the officers to detain the three
    men. The officers then proceeded to search the van.
 
    At the time they were detained, each of the three used an alias.
    During the initial search of the van, the officers failed to locate the
    drugs, money and the firearms, which were located within a secret
    compartment. However, two drug narcotics detection canines were
    brought to the scene. When the dogs alerted on the van, officers
    moved the van to another location where a search was conducted
    pursuant to a search warrant.
 
    Conspirator 1, Conspirator 2 and Rollack were transported to the police
    station without being placed under arrest. After providing false identification
    to the authorities, the three were released. They discussed among
    themselves whether to wait in Rockingham until the van was released
    or to flee the city because the officers might locate the secret compart-
 
                         4
    ment which contained the drugs, money and guns. Rollack urged
    them to stay.
 
    While using a pay phone to notify their associates in New York of
    their plight, the three were arrested. They were taken to the Sheriff's
    Department, and eventually placed under high bonds. Rollack's uncle
    and Conspirator 1's cousin provided bond money, and the three were
    able to bond out of jail several days later. Conspirator 1 never
    returned to North Carolina to face his charges, nor did he make any
    subsequent drug trips to North Carolina.
 
    While Conspirator 2 did not return to face his pending charges as
    well, he did continue to be involved in drug trafficking in North
    Carolina in 1995. Conspirator 2 associated himself with Conspirator
    5. Conspirator 5 arranged to have crack cocaine transported to North
    Carolina, and Conspirator 2 then distributed the drugs.
 
    In early 1996, while Conspirator 2 was still dealing with Conspirator
    5, Conspirator 2 spoke by phone with Rollack. At the time of the
    conversation with Rollack, Conspirator 2 owed Conspirator 5 money
    for a drug debt. During the telephone conversation, Rollack explained
    that the source of cocaine Conspirator 2 had received from Conspirator
    5 was, in fact, Rollack's uncle. Rollack explained that "[m]y uncle
    gave Conspirator 5 some cocaine to sell for me, so I could pay for my
    lawyer." Rollack went on to explain that the kilogram and a half of
    crack cocaine that Conspirator 5 fronted to Conspirator 2 actually
    belonged to Rollack, and that Rollack wanted his money. Conspirator 2
    agreed to reimburse Conspirator 5 for the drug debt and to loan
    Rollack additional money to pay for his lawyer. Conspirator 2
    estimates that he sent Rollack approximately $20,000 during 1995 and
    1996.
 
    At Rollack's trial, Conspirator 1 and Conspirator 2 testified, along with
    others who corroborated their stories. Also called to testify was Special
    Agent Terry Tadeo of the Bureau of Alcohol, Tobacco and Firearms.
    Agent Tadeo testified about the interception of Rollack's mail, pursuant
    to Federal search warrants, between December 17 and December 27,
    1997. The mail was seized from Rollack's jail cell. The mail which
    was seized was written in Bloods code. Also seized was a list
 
                        5
    of Bloods codes. Agent Tadeo testified that some of the items seized
    were in Rollack's handwriting, while some were not.
 
    Sergeant Louis Savelli of the New York City Police Department
    Citywide Anti-Gang Enforcement Unit testified as an expert witness
    in the field of gang-related codes and as an expert witness on the
    Bloods gang. Sergeant Savelli examined letters seized from Rollack's
    cell and testified as to the significance and importance of certain
    works and symbols. According to Sergeant Savelli, Bloods and other
    gang members frequently communicate with fellow gang members in
    code to avoid police detection.
 
    Sergeant Savelli went on to identify Bloods and SMM salutations
    and expressions in Rollack's correspondence. Agent Tadeo, in turn,
    summarized the contents of the seized writings and letters from Rol-
    lack's jail cell, and related them to the testimony presented by other
    witnesses at trial. Rollack was subsequently convicted by a jury, and
    sentenced to 40 years of imprisonment on Count I, and 5 years of
    imprisonment on Count II, to run consecutively.
 
    Rollack challenges his convictions, claiming: (1) the police did not
    have probable cause to search the Nissan Quest van immediately upon
    seizure; (2) the trial court erred by allowing testimony of prior bad
    acts occurring in times and places distant from the conduct alleged in
    the indictment; (3) the trial court erred by allowing introduction into
    evidence of multiple writings, rap songs and letters found in a search
    of the Defendant's jail cell and mail; (4) the trial court erred by allow-
    ing for a constructive amendment of the indictment when it permitted
    extensive testimony and documentary evidence about the activities of
    SMM, and about Defendant's role in that gang; (5) the trial court
    erred by allowing Agent Tadeo to summarize the contents of the writ-
    ings seized from Defendant's jail cell, and then relate the writings to
    the testimony of the witnesses at trial; (6) the trial court erred by
    refusing to give a requested multiple conspiracies' jury instruction;
    and (7) the trial court erred in applying sentencing enhancements for
    Rollack's leadership role and for obstruction of justice.
 
    I.
 
    The first issue for this Court is whether the trial court erred in not
    suppressing the evidence seized from the Nissan Quest. We will
 
                         6
    review the factual determinations of the lower court under a clearly
    erroneous standard. See United States v. Kitchens, 

, 31
    (4th Cir. 1997). The legal conclusions of the trial court are to be
    reviewed de novo. See United States v. Johnson, 

, 441
    (4th Cir. 1997).
 
    "The proponent of a motion to suppress has the burden of establish-
    ing that his own Fourth Amendment rights were violated by the chal-
    lenged search or seizure." Rakas v. Illinois , 

, 131 n.1
    (1978); accord United States v. Ramapuram, 

, 1155
    (4th Cir. 1980), cert. denied, 

(1981). To establish a
    violation of one's Fourth Amendment rights, a defendant must first
    show that he had a "reasonable expectation of privacy" in the place
    searched. See 

; United States v. Al-Talib, 

, 930 (4th Cir. 1995); United States v. Horowitz, 

, 1225 (4th Cir. 1986). If a defendant cannot make such a show-
    ing, the defendant cannot challenge the reasonableness of the search
    and seizure. See United States v. Rusher, 

, 873 (4th Cir.),
    cert. denied, 

(1992).
 
    A reasonable expectation of privacy is not created by the subjective
    expectation of the proponent alone. See Horowitz , 806 F.2d at 1225.
    Rather, to have a reasonable expectation of privacy the defendant
    must show he had control over the area searched; he had taken mea-
    sures to ensure privacy; and that society is willing to recognize defen-
    dant's expectation as reasonable. See id.
 
    Rollack claims that he had a reasonable expectation of privacy in
    the leased van in that the lease agreement for the van did not preclude
    him from driving; he had a property interest in the guns, money and
    drugs found in the van; and that he had secreted the contraband in a
    hidden compartment in the van. This, Rollack contends, shows a rea-
    sonable expectation of privacy in the van sufficient to allow him to
    challenge its search.
 
    We are not persuaded by this argument. The van was not leased in
    Rollack's name, nor did the lease explicitly permit Rollack to drive
    the van. Further, Rollack did not exercise control over the van by
    driving it. Rather, he was merely a passenger.
 
                        7
    In United States v. Wellons, 

(4th Cir. 1994), cert.
    denied, 

(1995), the defendant was arrested following
    the discovery of drugs in a rental car which he was driving but for
    which he was not listed as an authorized driver on the rental agree-
    ment. The defendant was pulled over by a West Virginia State
    Trooper, and the defendant told the Trooper that the vehicle had been
    rented by another. While the Trooper awaited verification of the
    rental agreement, he called for a narcotics-sniffing dog to be sent to
    the scene. The dog alerted the presence of narcotics and a subsequent
    search revealed cocaine and heroin. There, we rejected the notion that
    an unauthorized driver of a rental vehicle had a reasonable expecta-
    tion of privacy in the car he was driving.
 
    In the case before the Court, Rollack's expectation of privacy is even
    less compelling than that of the defendant in Wellons. In Wellons, the
    defendant, who had secreted the contraband in luggage in the car,
    exercised control over the vehicle as the driver when he was stopped
    for speeding by a State Trooper. According to Conspirator 2's
    testimony at trial, Rollack never drove the vehicle during their trip,
    and the vehicle was obtained by Conspirator 1. Therefore, Rollack is
    in the same position as the defendant in Wellons, except here Rollack
    never exercised any control over the vehicle. These facts lead this
    Court to the inevitable conclusion that Rollack never had a reasonable
    expectation of privacy in the van, hence he cannot object to the search
    as being illegal.
 
    II.
 
    The next issue before the Court is the admissibility of evidence
    pursuant to Rule 404(b) of the Federal Rules of Evidence. Our review
    is limited to determining whether the trial court abused its discretion.
    See United States v. Chin, 

, 87 (4th Cir. 1996); United
    States v. Haney, 

, 607 (4th Cir. 1990).
 
    Rule 404(b) dictates that "[e]vidence of other crimes, wrongs, or acts
    is not admissible to prove the character of a person in order to show
    action in conformity therewith." Fed. R. Evid. 404(b). However, Rule
    404(b) applies only to limit the admission of other acts extrinsic to the
    conduct charged in the indictment. See 

. Other
    criminal acts are considered "intrinsic" if they are "inextricably
 
                        8
    intertwined or both acts are part of a single criminal episode or other
    acts were necessary preliminaries to the crime charged." See 

    (adopting the standard of United States v. Lambert, 

,
    1007 (10th Cir. 1993)). In addition, evidence of other crimes or
    uncharged conduct is not considered "other crimes" for Rule 404(b)
    purposes if it "arose out of the same ... series of transactions as the
    charged offense, ... or if it is necessary to complete the story of the
    crime [on] trial." United States v. Kennedy, 

, 885 (4th Cir.
    1994) (quoting United States v. Towne, 

, 886 (4th Cir.
    1989)).
 
    Rollack contends that other acts or crimes introduced in the trial were
    not inextricably intertwined with, nor did they arise out of, the same
    series of transactions as the charged conspiracy. Hence, the other acts
    or crimes were extrinsic, and subject to the requirements of Rule
    404(b).
 
    Rollack goes on to describe the conspiracy as alleged as one which
    began in the Summer of 1994 between Rollack, Conspirator 1 and
    Conspirator 2, and which ended upon their arrest in Rockingham on
    October 22, 1994. Given this definition of the time frame of the
    conspiracy, Rollack argues that the evidence presented at trial
    concerning acts in 1993 and early 1994, the evidence pertaining to
    SMM's affiliation with the Bloods in 1996, and the evidence
    pertaining to Rollack's ownership of guns and other vehicles with
    secret compartments are all extrinsic to the charged drug conspiracy.
 
    However, it is well-settled that the time period of a conspiracy is
    determined by the evidence presented at trial, not the dates alleged in
    the indictment. See United States v. Jackson, 

, 1490
    (4th Cir. 1985). Conspirators are presumed to continue as members
    of a conspiracy absent affirmative evidence of termination of, or with-
    drawal from, the conspiracy. See United States v. Walker, 

, 49 (4th Cir. 1986).
 
    The indictment in this case alleged that Rollack was a member of
    a conspiracy "within the Western District of North Carolina and else-
    where." Evidence of Rollack's involvement with drug trafficking in
    the Bronx, Pittsburgh, North Carolina and South Carolina all per-
 
                        9
    tained to drug distribution by the persons named in the indictment and
    their associates.
 
    Evidence pertaining to SMM was also relevant to the crimes
    charged in the indictment, because Rollack was the leader of the
    gang, and the gang specialized in drug trafficking, including drug traf-
    ficking in North Carolina. Testimony by coconspirators about the
    transport of drugs from New York, through Pittsburgh, was an inte-
    gral part of the crime alleged and not extrinsic evidence. See gener-
    ally United States v. Banks, 

, 1054 (4th Cir. 1993), cert.
    denied, 

(1994). Also, there was no evidence that Rol-
    lack withdrew from the conspiracy upon his arrest in Rockingham. To
    the contrary, the evidence presented at trial showed that Rollack con-
    tinued in the drug trade, demanding payment from Conspirator 2 for
    the drug debt owed Conspirator 5.
 
    The Court is satisfied that the trial court did not abuse its discretion
    in determining that this evidence was intrinsic for purposes of Rule
    404(b). This evidence was not offered to prove bad character, but
    rather "to complete the story of the crime [on] trial."
 
    III.
 
    We next turn our attention to the third issue raised on appeal,
    whether the trial court erred by allowing introduction into evidence
    of multiple writings, rap songs, and letters found in a search of Rol-
    lack's cell. Our standard of review for the admission of coconspirator
    statements under Rule 801(d)(2)(E) of the Federal Rules of Evidence
    is abuse of discretion. See United States v. Hassan, 

, 731
    (4th Cir. 1993); see also United States v. Russell, 

,
    1104 (4th Cir. 1992), cert. denied, 

(1993).
 
    Under 21 U.S.C. § 846, the government need only prove an act
    showing the defendant's initial participation in the conspiracy, United
    States v. Covos, 

, 806 (8th Cir. 1989), which is then pre-
    sumed to continue until its end, or the defendant's withdrawal is affir-
    matively shown. See United States v. Sheffer, 

(4th Cir.
    1990). Where the defendant fails to show that he withdrew from a
    conspiracy, his membership is viewed as continuing for the duration.
    See United States v. Barsanti, 

, 437 (4th Cir. 1991);
 
                         10
    United States v. West, 

, 289 (4th Cir. 1990); see gener-
    ally United States v. Girard, 

, 1172-73 (5th Cir. 1984)
    (bid-rigging conspiracy went beyond awarding of contract and lasted
    until final payment was made); United States v. Helmich, 

, 549 (11th Cir. 1983) (conspiracy to transfer secret information
    lasted seventeen years after last act of transfer, until final payment
    was made); United States v. Mennuti, 

, 1035-36 (2d
    Cir. 1982) (arson conspiracy lasted after fire until the coconspirator
    received the payoff, which was used to purchase the torched prop-
    erty); United States v. Walker, 

, 1348-50 (9th Cir.
    1981) (fraudulent contract lasted until conspirators divided profits).
 
    Indeed, "[a]rrest of some coconspirators does not, as a matter of
    law, terminate a conspiracy." United States v. Grubb, 

,
    1109 (4th Cir. 1975). Even acts intended to conceal or cover-up the
    conspiracy may be in furtherance of its aims or goals. See United
    States v. Potamitis, 

, 788 (2d Cir. 1984).
 
    At trial, letters seized from Rollack's jail cell were introduced into
    evidence, and Sergeant Savelli then translated the documents, written
    in code, for the benefit of the jury. A handwriting analyst determined
    that all of the letters were written by Rollack except for a letter Rol-
    lack received from an associate and a document of which the analyst
    could not determine who was the author. The Court determined the
    letters written by Rollack were admissible pursuant to Federal Rule of
    Evidence 804(b)(3) as "admissions against interest by a party." The
    Court also allowed the letters which were not written by Rollack to be
    introduced into evidence, pursuant to Federal Rule of Evidence
    801(d)(2)(E), which allows for the introduction of statements by a
    coconspirator of a party.
 
    Rollack urges that the trial court erred in several ways. Specifi-
    cally, he says that the court never made clear in its ruling whether its
    decision that the "ongoing conspiracy headed by [Rollack] while he
    is in jail" was the same conspiracy charged in the indictment. If the
    court was referring to another conspiracy when it made its decision,
    then the evidence would be extrinsic and subject to the dictates of
    Rule 404(b).
 
    Further, Rollack contends that the court never weighed the admissi-
    bility of the evidence pursuant to Federal Rule of Evidence 403,
 
                         11
    which requires courts to weigh the relevance of evidence against its
    prejudicial nature. See Fed. R. Evid. 403. This is troubling to Rollack,
    as he claims the testimony by Sergeant Savelli was prejudicial, espe-
    cially Savelli's translation that "Peter Rolls" (an alias of Rollack) was
    "another term for murder."
 
    However, the evidence seized from Rollack's cell corroborated the
    testimony of other government witnesses about Rollack's role in
    SMM, and his continued involvement in the conspiracy alleged in the
    indictment. Contrary to Rollack's contentions, the District Court's
    voir dire hearing outside of the presence of the jury enabled the judge
    to weigh the probative value of the evidence versus its prejudicial
    impact.
 
    Upon review of the material outside of the presence of the jury, the
    court noted that there were references in the seized materials consis-
    tent with the testimony presented at trial. The attorney for the govern-
    ment argued that the materials were statements against interest of a
    party-opponent, and that the references in the materials were clearly
    relevant, as they referred to testimony in evidence.
 
    Sergeant Savelli's testimony indicated that the crossing-out of the
    letter "c" in the seized documents was a common practice among
    members of the Bloods and that Bloods frequently communicated in
    codes. This corroborated trial testimony that SMM became a chapter
    of the Bloods during the time of Rollack's leadership. In the seized
    materials, the writer refers to himself as "Pistol," which is consistent
    with trial testimony that the defendant was known as "Pistol Pete."
    References to "drop top" referred to drugs, and the reference to an
    associate is consistent with trial testimony about one of the unindicted
    coconspirators who made trips with Rollack to North Carolina.
 
    The reference equating "Peter Rolls" to "murder" may or may not have
    been unduly prejudicial, however we need not decide. If a party fails to
    object to the admission of evidence, it is reviewable by this Court only
    for plain error. See 

. Further, objections must be
    stated with specific grounds given to preserve the objection
    for appeal, or the reviewing court will review the trial court's actions
    for plain error. See Fed. R. Evid. 103(a)(1). Here, Rollack made only
 
                         12
    a general objection to a lengthy narrative containing the first reference
    and no objection at trial to the second reference.
 
    Further, neither passage referring to "Peter Rolls" implicates Rol-
    lack as being involved in murders, and both passages corroborate trial
    testimony that SMM as an organization did engage in murders. We
    cannot say the district court abused its discretion in allowing the let-
    ters not written by Rollack to be entered into evidence, as there is no
    indication in the record that Rollack affirmatively withdrew from the
    conspiracy, and the testimony of an associate at trial indicated that he
    viewed himself as a conspirator of Rollack. Further, we are satisfied
    that the judge applied Rule 403 to all of the evidence presented to him
    during the voir dire proceeding, and that it was not plain error for the
    court to allow testimony about "Peter Rolls."

    IV.

    Rollack next contends that the trial court improperly broadened the
    possible bases for conviction beyond those in the indictment by
    allowing extensive testimony and documentary evidence about the
    activities of SMM, and Rollack's role in SMM, thereby constructively
    amending the indictment. We review this issue de novo. See United
    States v. Marl, 

, 280 (4th Cir. 1995).
 
    Constructive amendment of an indictment occurs when there is a
    presentation of evidence and jury instructions both which work to
    change the elements of the offense charged, resulting in the defendant
    being convicted of a crime other than that charged in the indictment.
    See United States v. Schnabel, 

, 203 (4th Cir. 1991).
    However, a "variance which does not affect substantial rights shall be
    disregarded." Fed. R. Crim. P. 52(a); see Berger v. United States, 

, 92 (1935) ("substantial rights" are not affected by a variance
    when the defendant is sufficiently informed of the charges against
    him so that he can prepare a defense and not be surprised, and when
    the charge is sufficiently specific to protect him from subsequent
    prosecution for the same offense); United States v. Odom, 

, 118 (4th Cir. 1984) (a variance between the indictment and the
    evidence that does not modify the elements of a crime charged does
    not invalidate a conviction unless it prejudices the defendant); United
 
                        13
    States v. DeBrouse, 

, 389 (4th Cir. 1981) (defendant
    must demonstrate substantial prejudice on the record as a whole).
 
    Rollack contends that the introduction of evidence at trial of gang
    communications, drug trafficking and gun possession all occurring in
    New York impermissibly broadened the possible bases for conviction
    beyond those presented to the grand jury, resulting in a constructive
    amendment of the indictment. Rollack objected to the government's
    introduction of this evidence in limine. In any case, Rollack argues,
    constructive amendment of the indictment constitutes error per se,
    and it is conclusively presumed that the defendant has been preju-
    diced. See United States v. Floresca, 

, 711 (4th Cir.
    1994).
 
    However, Rollack's reliance on Floresca is misplaced. Floresca
    involved the district court's misinstruction to the jury, which broad-
    ened the possible bases for conviction beyond those presented to the
    grand jury, thus constructively amending the indictment. Rollack does
    not contend, nor is there any suggestion in the record, that the district
    court misinstructed the jury in the case before this Court.
 
    We believe that the testimony about SMM, drug trafficking and
    gun possession is relevant to the alleged drug conspiracy, and is not
    unduly prejudicial. Indeed, "[t]he jury is entitled to know the setting
    of the case." United States v. Dudley, 

, 262 (4th Cir.
    1991):
 
              One of the accepted bases for the admissibility of other
              crimes arises when such evidence furnishes part of the con-
              text of the crime or is necessary to a full presentation of the
              case, or is so intimately connected with and explanatory of
              the crime charged against the defendant and is so much a
              part of the setting of the case and its environment that proof
              is appropriate in order to complete the story of the crime on
              trial by proving the immediate context or res gestae, or the
              uncharged offense is so linked together in point of time and
              circumstances with the crime charged that one cannot be
              fully shown without proving the other ... and [is thus] part
              of the res gestae of the crime charged.
 
                         14
    Id.; accord 

; 

.
 
    While Rollack contends that improper jury instructions leading to a
    constructive amendment constitutes prejudice, nowhere does he
    claim that the court misinstructed the jury. Since such a claim is a
    necessary prerequisite to prove constructive amendment of an indict-
    ment, see 

, his claim of error fails, and the
    Court is satisfied upon de novo review that the evidence which Rol-
    lack objects to is part of the res gestae of the crime charged.
 
    V.
 
    Rollack next contends that the district court erred by allowing Spe-
    cial Agent Tadeo to summarize the contents of the writings seized
    from Rollack's jail cell, and then relate the writings to the testimony
    of witnesses called at trial. We review to ensure that the decision to
    allow the admission of this evidence was not arbitrary or irrational.
    See United States v. Johnson, 

, 1156 (4th Cir.), cert.
    denied, 

(1995) (citing United States v. Bailey, 

, 122 (4th Cir. 1993)); United States v. Loayza, 

, 264
    (4th Cir. 1997).
 
    In an "ordinary federal drug prosecution, neither a summary wit-
    ness's testimony nor a summary chart ... [will] be admissible pursuant
    to Rules 702 or 611(a) [of the Federal Rules of Evidence]," because
    such testimony is inherently dangerous in that it lends credibility to
    prior government witnesses and is likely to confuse the jury. 

. However, Rule 611(a) can be used as a basis for the
    admission of summary testimony when the testimony aids in ascer-
    taining the truth. 

"The complexity and length of the case
    as well as the numbers of witnesses and exhibits are considered in
    making [this] determination." Loayza , 107 F.3d at 264. Also, in mak-
    ing this determination the court must consider the prejudice which
    would result to the defendant by allowing the summary testimony.
    

. However, any "[p]rejudice may be dis-
    pelled by allowing the defendant an opportunity to cross-examine the
    individual [presenting the summary testimony]," 

, and by "ensuring that the district court properly instruct[s] the
    jury concerning the manner in which they [are] to consider the [sum-
    mary testimony]." 

.
 
                        15
    At the conclusion of the government's case-in-chief, the prosecutor
    called Agent Tadeo to testify and summarize the contents of the
    seized writings and letters from Rollack's jail cell, and to relate them
    to the testimony presented at trial. Agent Tadeo presented his sum-
    mary testimony after Sergeant Savelli translated the contents of the
    writings from Bloods code into English, for the benefit of the jury.
 
    Rollack contends that this was impermissible because his case is
    distinguishable from Johnson and Loayza on the basis of complexity.
    In Johnson, Rollack argues, this Court allowed the use of a summary
    chart due to the complexity of that case, where 45 witnesses testified
    over a two and one-half week drug conspiracy trial. 

In
    Loayza, this Court permitted the use of summary charts in a complex
    Ponzie scheme case which included 13 government witnesses and 130
    government exhibits. 

.
 
    Rollack argues that his case is not complex because at trial testi-
    mony was presented by only five cooperating government witnesses;
    three Rockingham police officers, who testified mainly about chain-
    of-custody issues; and Agent Tadeo and Sergeant Savelli. Further, the
    time frame of the conduct alleged in the conspiracy was only ten
    months. Last, Rollack also argues that the limited usefulness of sum-
    mary testimony in his case is outweighed by the danger of prejudice
    to Rollack.
 
    The flaw in Rollack's argument is that he defines whether a case
    is complex by the number of witnesses called. According to this argu-
    ment, if there were only a few witnesses, the case must not have been
    complex. However, our prior cases make clear that when determining
    whether or not to allow summary testimony, courts are to consider the
    complexity of the case, the length of the case and the number of wit-
    nesses called. 

. Courts are not
    to use the witness lists as a proxy for complexity. Complexity is a
    separate determination.
 
    In the instant case, the government correctly points out that this was
    not a typical drug conspiracy in that material and relevant evidence of
    the conspiracy included cryptic letters and codes seized from Rollack's
    jail cell. Such documents were not immediately self- explanatory, and
    their content and context were not self-evident.
 
                         16
    Also, while Rollack may claim that the time frame of the conduct
    alleged in the conspiracy was only ten months, this Court has already
    determined that various acts performed over a series of years ranging
    from 1993 to 1996 were intrinsic for purposes of proving the conspir-
    acy. This fact makes it more likely that the summary testimony served
    to aid the jury in ascertaining the truth.
 
    Further, the district court weighed the danger of prejudice to Rol-
    lack, and dispelled this prejudice by allowing Rollack to cross-
    examine Agent Tadeo, and through giving proper limiting instruc-
    tions. The district court made clear how the jury was to consider the
    evidence when it said:
 
              "Members of the jury, Agent Tadeo has been permitted to
              testify to summarize certain aspects of these exhibits. A
              summary is not evidence. The evidence is the exhibits and
              the translation from Officer Savelli. Those are the evidence,
              and that's what you should consider. [Officer Tadeo] has
              been permitted to summarize the exhibits as to those por-
              tions that are, or some of which the Government contends
              are connected to the conspiracy that's the subject of this
              case, and you will receive further instructions limiting your
              consideration of these exhibits as the final instructions are
              given."
 
    Given the complex nature of the evidence presented, the multi-year
    time frame of the acts which made up the conspiracy, and the limiting
    instructions of the district court, we cannot say the district court acted
    in an arbitrary or irrational fashion in allowing the admission of the
    summary testimony.
 
    VI.
 
    Rollack's sixth ground for appeal is his contention that the district
    court erred by refusing to give a requested single versus multiple con-
    spiracies' charge. Failure to give a jury charge requested by the defen-
    dant constitutes reversible error where the trial court's refusal was
    clearly erroneous. See United States v. Mills , 

, 485 (4th
    Cir. 1993).
 
                         17
    Rollack contends that the court should have given his instruction
    concerning single versus multiple conspiracies because the court
    never made a specific finding that there was but one conspiracy
    proved by the evidence. It is Rollack's argument that at trial evidence
    unrelated to the conspiracy in Count I of the indictment was intro-
    duced that could have been construed by the jury to be evidence of
    entirely separate conspiracies. Rollack points to the testimony of
    Conspirator 1, where Conspirator 1 testified about matters occurring
    before Conspirator 1 and Conspirator 2 decided to broker drug deals
    in North Carolina. Rollack also points to the documentary evidence
    obtained from the search of his jail cell, more than two years after
    Rollack, Conspirator 1 and Conspirator 2 were arrested in
    Rockingham.
 
    Evidence that a conspiracy pre-dated and post-dated the dates
    alleged in the indictment does not create an inference that more than
    one conspiracy may have existed. See generally 

; United States v. Del Purgatoria, 

, 86-87 (2d
    Cir. 1969). "A single conspiracy exists where there is `one overall
    agreement,' United States v. Leavis, 

, 218 (4th Cir.
    1988) (quoting United States v. Bloch, 

, 1215 (9th Cir.
    1982), or `one general business venture.'" 

States
    v. McGrath, 

, 367 (2d Cir. 1979)).
 
    Defendants are not automatically entitled to an instruction about
    multiple conspiracies. Only when such an instruction is supported by
    the facts need a court provide such an instruction. See 

; United States v. Crockett, 

, 1316 (4th Cir.
    1987). That some of the actors in the conspiracy did not know each
    other does not change the conclusion. Members of a single conspiracy
    need only be aware of the larger conspiracy. See United States v.
    Richards, 

, 1309 (4th Cir. 1984).
 
    A multiple conspiracy instruction is not required unless the evidence
    at trial shows that defendants were involved only in separate
    conspiracies unrelated to the overall conspiracy charged in the indict-
    ment. See 

. Moreover,"[e]ven if the evidence
    were read to support a multiple conspiracy instruction, the district
    court's failure to give such an instruction is not reversible error
    `unless the defendants demonstrate that they have been prejudiced by
    the variance between the single conspiracy charged in the indictment
 
                        18
    and the multiple conspiracies proven at trial.'" 

n.1 (quoting
    United States v. Curry, 

, 1052 (7th Cir. 1992)).
 
    Indeed, when a defendant alleges a variance between pleadings and
    proof based upon evidence of supposed multiple conspiracies the
    defendant must show that the variance infringed upon a "substantial
    right" and thereby resulted in actual prejudice. See 

In other
    words, the defendant must show that evidence of multiple, separate
    conspiracies likely confused the jury, causing it to "transfer evidence
    from one conspiracy to a defendant involved in an unrelated conspir-
    acy." Id.
 
    We need not address the issue of whether Rollack's "substantial
    rights" were prejudiced, because we believe the district court's refusal
    to give the multiple conspiracies' instruction was not clearly errone-
    ous. While it is conceivable that the Rollack/Conspirator 1 trips to
    Pittsburgh constituted one conspiracy, the Rollack/Conspirator
    1/Conspirator 2 dealings were another, and the Rollack/Conspirator 2
    conversations were yet a third, the facts presented show that Rollack
    was the central figure uniting these groups in one large conspiracy.
    And where the facts presented at trial show one individual working
    with different groups, which are aware of one another, it is not clearly
    erroneous for the district court to refuse to give a multiple
    conspiracies instruction. See 

 
    VII.
 
    The seventh, and last, ground for appeal raised by Rollack is that the
    district court erred in applying sentencing enhancements for a
    leadership role in the conspiracy, and for obstruction of justice,
    despite a lack of evidence with sufficient indicia of reliability. The
    standard of review regarding factual findings by the district court dur-
    ing the sentencing of a defendant is whether the court was clearly
    erroneous in its findings. See United States v. Melton, 

,
    1332-33 (4th Cir. 1992); United States v. Daughtrey, 

,
    217 (4th Cir. 1989). When the sentencing issue on appeal raises
    "purely legal issues," the standard of review is de novo. 

.
 
    Adjustments for a defendant's role in the offense cannot be based
    on the conduct of a coconspirator or a co-defendant. See United States
 
                         19
    v. Moore, 

, 176 (4th Cir. 1994). In other words, Rollack
    should be judged on "an individualized determination of [his] culpa-
    bility." Id.
 
    Rollack contends that the evidence at trial established that in his
    dealings with Conspirator 1 and Conspirator 2 he was nothing more
    than "muscle," not the leader. It was Conspirator 2 and Conspirator
    1 who were managing and leading the transactions and
    conspirators, Rollack contends.
 
    According to the presentence report prepared by the United States
    Probation Office, "Peter Rollack was the organizer and leader of a
    drug conspiracy in the Western District of North Carolina and else-
    where," and "Mr. Rollack organized a gang known as `Sex, Money
    and Murder' which later became a `blood' gang."
 
    Testimony at trial supported these findings. To be sure, on trips to
    Pittsburgh and North Carolina, Rollack worked as an enforcer. How-
    ever, he also contributed capital for drug purchases. Further, on the
    third and final trip to North Carolina, half of the drugs in the Nissan
    Quest were Rollack's and half were Conspirator 1's.
 
    If this was all of the evidence indicating Rollack's leadership, then
    the application of the enhancement might be a close call. However,
    there was much more. When Conspirator 4 failed to pay his drug
    debt, it was Rollack who made the decision that Conspirator 4 was
    to be killed. When Rollack, Conspirator 1 and Conspirator 2 were
    released while the police were conducting a search of their vehicle
    in Rockingham, it was Rollack who made the decision that the
    three men should wait for the van to be released rather than fleeing.
 
    Furthermore, Rollack was the leader of SMM during the period
    alleged in the indictment. SMM was supplying kilograms of cocaine
    powder and cocaine base that were being distributed in New Jersey,
    Pittsburgh and North Carolina. The testimony of Agent Tadeo during
    the sentencing hearing further established that Rollack continued to
    exercise control and maintain his leadership position in SMM after he
    was transported to a North Carolina jail.
 
    Even after the episode in Rockingham, Rollack continued to exer-
    cise direct influence over the North Carolina drug trade through his
 
                        20
    associates. In early 1996, Conspirator 2 was purchasing quantities of
    crack cocaine from Conspirator 5. Rollack telephoned Conspirator 2 in
    Charlotte. Rollack explained that the kilogram and a half of crack
    cocaine that Conspirator 5 fronted to Conspirator 2 actually belonged
    to Rollack, and that he wanted his money. Given the extensive nature
    of this evidence, we cannot say the district court was clearly erroneous
    in applying the leadership enhancement.
 
    Regarding the obstruction of justice enhancement, Rollack objected
    to this in his presentence report. The court applied this enhancement,
    though, finding that the letters and writings seized from Rollack's jail
    cell and mail "reflect continuing, ongoing exultations to gang mem-
    bers in New York to kill witnesses."
 
    It is appropriate for a district court to apply an obstruction of justice
    enhancement when a "defendant either threaten[s] the codefendant,
    witness, or juror in his or her presence or issue[s] the threat in
    circumstances in which there is some likelihood that the codefendant,
    witness, or juror will learn of the threat." United States v. Brooks, 

, 1149-50 (4th Cir. 1992). Rollack contends that the
    obstruction adjustment should not apply in his case because, like in
    Brooks, there is no evidence that the threatened witness knew of Rol-
    lack's threats, nor that Rollack acted on his threats.
 
    At the sentencing hearing Agent Tadeo testified about a letter sent
    by Rollack in September, 1997 to SMM associates in New York with
    instructions for gang members to kill David "Twin" Mullins, because
    Rollack believed that Twin was a potential witness against him. A
    second, similar letter from Rollack was read at a meeting in New
    York during November, 1997. Twin was later murdered in the Bronx
    on Thanksgiving Day, 1997.
 
    Agent Tadeo further testified about the contents of letters seized
    from Rollack's jail cell. One letter contained a "to do" list, instructing
    fellow gang members not to use their real names and urging them to kill
    "snitches." Another letter instructed an associate to "keep the circle
    tight" and "to take care of all of the orders to kill." Agent Tadeo, who
    had reviewed hundreds of letters seized from Rollack's cell, testified that
    it was his opinion that Rollack was attempting to maintain control of
    SMM through the letters. Agent Tadeo also testified that after seizing
 
                         21
    the letters and learning of Rollack's instructions that cooperating wit-
    nesses should be killed, it became necessary to relocate Conspirator
    5, a cooperating witness who later testified at Rollack's trial.
 
    In fashioning his argument that his case is similar to the one in
    Brooks, Rollack conveniently disregards, as he must, the portion of
    Brooks which says obstruction adjustments are appropriate when the
    threat is issued in "circumstances in which there is some likelihood
    that the codefendant, witness, or juror will learn of the threat." Based
    on the defendant's history of crimes of violence and the murder of
    Twin on Thanksgiving Day, 1997, there was a considerable likelihood
    that cooperating witnesses (Conspirator 5 in particular) and
    government informants were likely to learn of the defendant's threats.
    Rollack knew the instructions in the letters were going to be shared
    with his associates, and it was his purpose to silence those, whether it
    be through death or coercion, who were going to turn on him. We
    cannot say the trial court was in error in applying this enhancement.
 
    VIII.
 
    In conclusion, we find no error, reversible or otherwise, in the dis-
    trict court's various rulings. Appellant's conviction and sentence is,
    hereby,
 
    AFFIRMED.
 
                         22