Assessing The Credibility Of A Cooperating Witness

In cocaine distribution conspiracy trial, excluding proposed defense expert attorney witness to opine on "the ramifications of the [cooperating] codefendants' plea agreements" concerning the credibility of a cooperating witness because under FRE 702, this was a matter that the jury could decide for itself without the aid of expert evidence, in United States v. Allen, _ F.3d _ (4th Cir. April 26, 2013) (No. 12-4168)

The ability to assess the credibility of a witness remains an important role for the jury, particularly for cooperating witnesses. While meaningful cross-examination is normally permitted, what other tools can be employed to highlight witness credibility? The Fourth Circuit recently explained how understanding a witness's motivations did not require expert testimony when a witness's motivations were a matter of "common sense." To the extent a jury needs to be vigilant in this regard, the matter can normally be adequately addressed by providing a cautionary jury instruction.

In the case, defendant Allen was charged as part of a cocaine base distribution conspiracy for serving as the "back up" source for cocaine when the usual conspiracy provider was unable to make delivery. As noted by the circuit, the government ably provided "mountainous evidence [that] showed that the [conspiracy's] drug network operated" in the manner of a drug distribution chain. The co-conspirators on the chain included street-level dealers who "sold $5 and $20 crack rocks in low-income neighborhoods." The street dealer supply came from "higher up in the distribution chain" of middle-men who "would in turn buy crack cocaine from Chrissawn Folston. Finally, Folston would buy his supply of crack cocaine from Willie Chappell, who supplied the drug to him in bulk. The government further claimed that when Chappell was unable to supply crack cocaine, Folston turned to [defendant] Allen as the back-up supplier. Allen, _ F.3d at _. The defendant did not challenge this evidence and conceded that "the evidence introduced at trial sufficiently detailed th[e conspiracy's] operating scheme." However, the defendant argued that the government was wrong in claiming he was the back-up supplier for the distribution chain. Rather, his arrest was the result of a one-time sale of "3.5 ounces of crack cocaine to Folston" which did not establish "knowledge of a broader conspiracy," which was an element of the drug conspiracy. Allen, __ F.3d at __.

Cooperating witness Folston was offered to show the connection of defendant Allen with the Folston conspiracy. In order to impeach or undermine the witness's testimony, the defendant offered "expert testimony to help explain the ramifications of his codefendants’ [Folston's] plea agreements with the government." The defendant hoped the expert could highlight the "sweetheart deal," implying that this affected the credibility of the witness's testimony. The trial judge refused the expert evidence proffer and after the defendant was convicted, he appealed citing this decision as one of the grounds of the appeal.

The Fourth Circuit affirmed the trial court's decision not to admit the proffered expert evidence, finding that:

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

As the circuit explained, it would also be a misuse of FRE 702 to put on an expert witness simply to provide impeachment evidence:

Given the nature of the requested expert testimony, the district court did not err in denying Allen's motion to admit expert testimony. Expert testimony of this nature is not permitted under the Federal Rules of Evidence. Moreover, in an abundance of caution, the district court admonished the jury to examine more carefully the testimony of witnesses that may be motivated by the desire to escape punishment. Finding no error in the district court's rulings on Allen's pretrial motions, we see nothing in the record that warrants vacating Allen's conspiracy conviction.
Allen, __ F.3d at __ .

While the circuit did not address the trial judge's wording of his cautionary instruction regarding the cooperating codefendant, these type of instructions are commonly available as part of the model criminal jury instructions suggested by various circuits. As one example, consider the model instruction from the Ninth Circuit:

Ninth Circuit Criminal Jury Instruction 4.9

Testimony of Witnesses Involving Special Circumstances—Immunity, Benefits, Accomplice, Plea

You have heard testimony from [name of witness], a witness who [received immunity. That testimony was given in exchange for a promise by the government that [the witness will not be prosecuted] [the testimony will not be used in any case against the witness]];

[received [benefits] [compensation] [favored treatment] from the government in connection with this case];

[[admitted being] [was alleged to be] an accomplice to the crime charged. An accomplice is one who voluntarily and intentionally joins with another person in committing a crime];

[pleaded guilty to a crime arising out of the same events for which the defendant is on trial. This guilty plea is not evidence against the defendant, and you may consider it only in determining this witness's believability].

For [this] [these] reason[s], in evaluating the testimony of [name of witness], you should consider the extent to which or whether [his] [her] testimony may have been influenced by [this] [any of these] factor[s]. In addition, you should examine the testimony of [name of witness] with greater caution than that of other witnesses.


The instruction to consider accomplice testimony with “greater caution” is appropriate regardless of whether the accomplice's testimony favors the defense or prosecution. United States v. Tirouda, 394 F.3d 683, 687–88 (9th Cir. 2005), cert. denied, 547 U.S. 1005 (2006). The Committee recommends giving this instruction whenever it is requested.

For more jury instructions, see Model Federal Jury Instructions.


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