Overcoming Potential Prejudice In The Dual Fact/Expert Law Enforcement Witness

Problems in dual role were noted and avoided in United States v. Farmer, 543 F.3d 363 (7th Cir. Sept. 9, 2008) (Nos. 07-2505, 07-3313, 07-2506, 07-2507)

The rules recognize that the same witness can provide both lay and expert testimony. See, e.g., FRE 701 ACN (2000 Amendment) (noting “it is possible for the same witness to provide both lay and expert testimony in a single case”). However, special issues can arise when a law enforcement witness testifies as a lay (or fact) and expert witness. This issue was considered recently by the Seventh Circuit.

Co-defendant Ellis was prosecuted as part of a conspiracy to distribute cocaine, cocaine base, and marijuana. The evidence of his involvement included recordings obtained based on court-authorized wire taps. At trial, lead case Agent Rehg “testified as a fact witness regarding the investigation’s progress and events, and as an expert witness to assist the jury in understanding the coded drug language contained in the recorded conversations,” based on his training and experience. Farmer, 543 F.3d at 369. Over defense objection, the trial court permitted the agent to testify as a fact and expert witness but gave a limiting instruction concerning the expert testimony. After his conviction, defendant Ellis was sentenced to 288 months’ imprisonment.

The Seventh Circuit acknowledged that jury confusion can arise by the dual use of a fact and expert law enforcement witness. However, dual use testimony may be permitted where the potential for prejudice is addressed through precautions taken by the court, including by limiting instructions and structured examination that signals the different types of testimony being offered. As the circuit explained:

“The district court required the government to establish the proper foundation for Agent Rehg’s knowledge of the coded drug language prior to him testifying to those meanings. The government also prefaced Agent Rehg’s expert testimony by asking him the coded language’s meaning ‘based on [his] expertise.’ Furthermore, the district court gave the appropriate cautionary instruction regarding expert testimony, instructing the jury that it could judge that testimony the same way it judges fact witnesses’ testimony, and could ‘[g]ive the testimony whatever weight you think it deserves. . . .’ The district court also allowed Ellis’s attorney to extensively cross-examine Agent Rehg about the coded drug terms used in the calls, his familiarity with other drug terms, and the factual aspects of his direct testimony. Ellis’s attorney critically questioned Agent Rehg about his expert opinion on the coded language, noting that according to him, ‘shoes,’ ‘block,’ and ‘chicken’ were just a few of many commonly used words that he claimed meant cocaine. This thorough crossexamination highlighted the parts of Agent Rehg’s testimony that were garnered from his expert opinion, which further clarified the testimonial capacities for the jury. In light of these safeguards, any risk that the jury could have confused Agent Rehg’s direct observations with his expert knowledge of the code words was adequately alleviated.”
Farmer, 543 F.3d at 371 (citations and footnote omitted). It would have been more helpful if the prosecutor had began each question calling for expert testimony by asking if it was based on the agent’s expertise or training and experience. Farmer, 543 F.3d at 371 n.2. The failure to take this additional step was not fatal.

The Farmer case notes the special concerns raised by the use of dual expert testimony and the steps that may be taken to ameliorate the potential for prejudice and confusion.


  • Prior Federal Evidence Review: The issue of using fact and expert law enforcement witness testimony was thoroughly considered in: Lead Story: “Steps For Avoiding Potential Prejudice, Confusion And Other Problems In Using Law Enforcement Dual Fact and Expert Witnesses,” 4 Fed. Evid. Rev. 1752 (Dec. 2007).
Federal Rules of Evidence
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