                       United States Court of Appeals
                             FOR THE EIGHTH CIRCUIT
                                     ___________

                                     No. 97-3450
                                     ___________

United States of America,                *
                                         *
             Appellee,                   *
                                         *    Appeal from the United States
      v.                                 *    District Court for the
                                         *    District of Minnesota.
Flavio Diaz Santana,                     *
                                         *
             Appellant.                  *
                                     ___________

                                Submitted: March 10, 1998

                                     Filed: July 24, 1998
                                     ___________

Before WOLLMAN and LOKEN, Circuit Judges, and BATAILLON,1 District Judge.
                           ___________

WOLLMAN, Circuit Judge.

       Flavio Diaz Santana appeals from the judgment entered by the district court2 on
his convictions for conspiracy to distribute and possess with intent to distribute cocaine




      1
        The HONORABLE JOSEPH F. BATAILLON, United States District Judge
for the District of Nebraska, sitting by designation.
      2
      The Honorable David S. Doty, United States District Judge for the District of
Minnesota.
in violation of 21 U.S.C. § 846 and for aiding and abetting the possession with intent to
distribute cocaine in violation of 21 U.S.C. § 841(a)(1). We affirm.

                                            I.

        In October of 1996, Bill Wyffels, a law enforcement officer with the Eden Prairie
Police Department and a member of the Southwest Hennepin Drug Task Force, received
information from a confidential informant that a man named Gerardo Arellano was
selling cocaine in Shakopee, Minnesota. After independently corroborating certain
aspects of the informant’s report, Officer Wyffels and other members of the drug task
force began surveillance of Arellano’s residence. On October 22, the informant, acting
under the direction of the officers, set up a controlled buy in which he was to purchase
one ounce of cocaine from Arellano. Following the successful completion of this
purchase, the officers obtained a search warrant for Arellano’s apartment. The officers
did not immediately execute the warrant, however, and instead instructed the informant
to set up another buy, this time for fifteen ounces of cocaine. The informant contacted
Arellano by telephone on October 30. Arellano told the informant that he needed to
contact his supplier in order to find out if he could obtain the drugs. Arellano called
back a short time later, telling the informant that his supplier was delivering the cocaine
from Minneapolis and that they could meet in about twenty minutes.

       The officers set up surveillance around Arellano’s apartment. After a short while,
they observed an automobile approach and come to a stop. The driver, later identified
as Diaz, and a passenger, Timeteo Ruiz, exited the vehicle and accompanied Arellano,
who had been waiting outside, into Arellano’s apartment. Arellano and the informant
then met as scheduled at a local bar before returning to the apartment. Once inside the
apartment, Arellano showed the informant a large plastic sack containing numerous
plastic bags filled with cocaine. After inspecting the drugs, the informant left the
apartment, explaining that he needed to retrieve the money from his vehicle.



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       The officers then executed the search warrant, discovering during the search a
plastic sack, near which Diaz was standing, containing fifteen individual packages, each
of which contained one ounce of cocaine. The officers also discovered 16 grams of
cocaine in the pocket of a shirt hanging in Arellano’s closet and 35.2 grams of cocaine
in the trunk of Arellano’s car. The search also resulted in the discovery of $3,449 in
cash. Of this total, Diaz carried $2,059, Ruiz carried $360, and the remainder was found
in the shirt in Arellano’s closet. In addition, the officers discovered Arellano’s phone
number in Diaz’s wallet. Lastly, fingerprint analysis of the seized cocaine packages
revealed a solitary fingerprint belonging to Diaz.

        A grand jury returned a three-count indictment against Arellano, Diaz, and Ruiz.
Counts I and III charged each defendant with conspiracy to distribute and possess with
intent to distribute cocaine in violation of 21 U.S.C. § 846 and with aiding and abetting
the possession with intent to distribute cocaine in violation of 21 U.S.C. § 841(a)(1).
Count II was returned against Arellano only, and charged him with distribution of
cocaine in violation of 21 U.S.C. § 841(a)(1). After the indictment was returned, Ruiz
apparently fled the area, and his whereabouts are unknown. Arellano agreed to plead
guilty and cooperate with the government. Diaz rejected a similar plea bargain, choosing
instead to proceed to trial.

      Arellano testified that Diaz had been supplying him with cocaine for
approximately three months, beginning in August of 1996. A typical delivery consisted
of approximately two ounces of cocaine. Initially, Arellano received about two
deliveries per week. The frequency of the deliveries steadily increased as Arellano
began to develop a customer base. By October of 1996, Arellano was receiving two-
ounce deliveries on a daily basis. Arellano also testified that on the day of his arrest he
had contacted Diaz about obtaining fifteen grams of cocaine and that Diaz had
subsequently delivered the cocaine found in the apartment.




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      Diaz testified on his own behalf, denying Arellano’s allegations. He testified that
he had driven Ruiz to Shakopee as a favor and had no knowledge about the nature of
Ruiz’s dealings with Arellano. He claimed not to have known that Ruiz and Arellano
were involved in a cocaine transaction until shortly before the police arrived, at which
time he decided to investigate the contents of the plastic sack. He claimed that he then
picked up one of the individual bags, thereby explaining the presence of his fingerprint.

        The jury returned a verdict finding Diaz guilty of both charged counts. The
district court sentenced him to 78 months’ imprisonment, the lowest possible sentence
in the applicable range. Diaz now appeals.

                                           II.

      Diaz first contends that his trial was marked by numerous defects, including
prosecutorial misconduct and erroneously admitted expert testimony.

       We begin with Diaz’s allegations of prosecutorial misconduct. He contends that
statements made and testimony elicited by the government constituted improper
bolstering of or vouching for Arellano’s credibility. Improper vouching may occur when
the government: (1) refers to facts outside the record or implies that the veracity of a
witness is supported by outside facts that are unavailable to the jury; (2) implies a
guarantee of truthfulness; or (3) expresses a personal opinion about the credibility of a
witness. See United States v. Beasley, 102 F.3d 1440, 1449 (8th Cir. 1996), cert.
denied, 117 S. Ct. 1856 (1997).

       Diaz points to two instances of improper vouching. First, the government asked
Arellano to explain the terms of his plea agreement, to which Arellano simply replied,
“Just to tell the truth.” Second, the government stated in its closing argument that “the
government doesn’t want anyone convicted on anything less than the truth.” Diaz argues
that these instances reflect an attempt on behalf of the government to act as a



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guarantor of truthfulness. We disagree. Our decisions establish that “[e]vidence of the
existence, the terms, and the witness’s understanding of a plea or witness immunity
agreement is not vouching.” Id. at 1450; see also United States v. Magee, 19 F.3d 417,
421 (8th Cir. 1994). With respect to the government’s closing remarks, the prosecutor
did not express a personal opinion regarding Arellano’s credibility, did not make any
guarantees of truthfulness, and did not imply that she knew something that the jury did
not. See Beasley, 102 F.3d at 1449. We therefore conclude that there was no
impermissible vouching in this case.

      We have considered Diaz’s other allegation of prosecutorial misconduct and
conclude that it is without merit.

       Diaz next contends that the district court abused its discretion in admitting the
testimony of Captain Eldon Fontana of the Hennepin County Police Department. Diaz
complains that Fontana was improperly allowed to testify regarding the frequency with
which fingerprints are recovered from plastic bags. We review a district court’s decision
to admit expert testimony for a clear abuse of discretion. See United States v. Chard,
115 F.3d 631, 635 (8th Cir. 1997).

        Rule 702 of the Federal Rules of Evidence provides that an expert witness may
be qualified “by knowledge, skill, experience, training, or education . . . .” Here,
Fontana had twenty-six years of experience in law enforcement, including extensive
experience in drug-related investigations. The crime lab that performed the fingerprint
testing in this case was under his command. Fontana’s experience and knowledge
qualified him to testify regarding how common it was for the crime lab to recover
adequate fingerprints from plastic bags. His testimony was relevant and helpful to the
jury in that it concerned matters beyond the general knowledge of average individuals.
See United States v. Shedlock, 62 F.3d 214, 219 (8th Cir. 1995). Thus, the district court
did not abuse its discretion in admitting his testimony.




                                          -5-
                                            III.

        Diaz also claims that his trial counsel rendered ineffective assistance. Because
ineffective assistance claims generally cannot be established without the development
of facts outside the record, they should be raised in the context of a proceeding brought
under 28 U.S.C. § 2255. See United States v. Hawkins, 78 F.3d 348, 351-52 (8th Cir.
1996), cert. denied, 117 S. Ct. 126 (1996). We will consider such a claim on direct
appeal only in those exceptional cases in which the district court has developed a record
on the ineffectiveness issue or where the result would otherwise be a plain miscarriage
of justice. See United States v. Reddix, 106 F.3d 236, 238 (8th Cir. 1997). This is not
such a case, and thus we decline to address the ineffective assistance claim in this
proceeding.

                                            IV.

        Diaz argues that his separate convictions for conspiracy to possess cocaine with
intent to distribute and for aiding and abetting the possession of cocaine with intent to
distribute violated the Double Jeopardy Clause of the Fifth Amendment. Diaz did not
raise this claim in the district court, and it is well settled that “[d]ouble jeopardy claims
may not be raised for the first time on appeal.” United States v. Goodwin, 72 F.3d 88,
91 (8th Cir. 1995). In any event, Diaz’s argument is precluded by United States v.
Thomas, 971 F.2d 147 (8th Cir. 1992), which holds that separate convictions identical
to those in the present case do not constitute a violation of the Double Jeopardy Clause.
971 F.2d at 149.

                                             V.

      Diaz next contends that the evidence was insufficient to support his conviction.
When reviewing the sufficiency of the evidence, we view the evidence in the light most
favorable to the verdict and give the government the benefit of all reasonable



                                            -6-
inferences. See United States v. Diaz-Diaz, 135 F.3d 572, 577 (8th Cir. 1998). We will
reverse “‘only if a reasonable jury must have had a reasonable doubt’ that the elements
of the crime were established.” United States v. Carlisle, 118 F.3d 1271, 1273 (8th Cir.
1997), cert. denied, 118 S. Ct. 429 (1997) (quoting United States v. Bordeaux, 84 F.3d
1544, 1547 (8th Cir. 1996)).

       Diaz’s argument rests almost exclusively on his assertion that Arellano’s
testimony was not credible and should have been disregarded. Assessing the credibility
of witnesses is a matter properly left to the jury. See United States v. Anderson, 78 F.3d
420, 422-23 (8th Cir. 1996). The jury heard extensive testimony from Arellano that Diaz
had supplied him with a substantial amount of cocaine during August, September, and
October of 1996. This testimony, which the jury apparently found credible, was clearly
sufficient to support Diaz’s conviction.

                                            VI.

        Diaz’s final contention is that the district court made two errors during sentencing.
First, he argues that his offense level should have been decreased pursuant to U.S.S.G.
§ 2D1.1(b)(6), which reduces the offense level for those defendants who qualify for the
safety valve exception set forth in U.S.S.G. § 5C1.2. Passing the fact that Diaz raises
this issue for the first time on appeal, his argument is without merit. To qualify for the
safety valve exception, a defendant carries the burden of demonstrating that “he has
truthfully provided to the Government all information regarding the relevant crime before
sentencing.” United States v. Velasquez, 141 F.3d 1280, 1283 (8th Cir. 1998); see also
U.S.S.G. § 5C1.2(5). There is nothing in the record indicating that Diaz provided any
information whatsoever regarding the relevant crime prior to his sentencing.

      Diaz asserts that the district court erred in calculating the quantity of cocaine for
sentencing purposes. We review a district court’s drug quantity calculations for clear




                                            -7-
error, and we will reverse only if our examination of the entire record “definitely and
firmly convinces us that a mistake has been made.” United States v. Moss, 138 F.3d
742, 745 (8th Cir. 1998) (quoting United States v. Sales, 25 F.3d 709, 711 (8th Cir.
1994)). Moreover, a district court’s findings regarding the credibility of witnesses “are
virtually unreviewable on appeal.” United States v. Karam, 37 F.3d 1280, 1286 (8th Cir.
1994). In arriving at Diaz’s base offense level of 26, the court determined that the
quantity of cocaine attributable to Diaz was at least 500 grams but less than 2 kilograms.
Diaz does not dispute that the 476 grams of cocaine seized during the search were
properly attributed to him. However, he argues that the district court erred in
determining that he was accountable for a total quantity of at least 500 grams.

        Diaz’s argument is meritless. The district court’s determination was supported
by the testimony of co-defendant Arellano, who testified that during the course of the
conspiracy he received numerous multi-ounce deliveries of cocaine from Diaz. That
testimony, which the court expressly found credible and reliable, was clearly sufficient
to justify a quantity determination of more than 500 grams.

      The judgment is affirmed.

      A true copy.

             Attest:

                     CLERK, U.S. COURT OF APPEALS, EIGHTH CIRCUIT.




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