Plain Error Results In Using Dual Fact And Expert Witness

Sixth Circuit reverses conviction based on trial court’s failure to clearly demark between the agents’ expert and lay testimony and failure to give a cautionary instruction about the dual roles of agent’s testimony, which was plain error, in United States v. Lopez-Medina, 461 F.3d 724 (6th Cir. 2006)

As previously posted, special problems may arise where a law enforcement witness testifies as both a fact and expert witness at trial. A Sixth Circuit case considered the issue and concluded plain error resulted from the dual testimony.

In the case, after an investigation, the DEA executed a search warrant at the residence of defendant Medina. The agents seized “used and unused plastic heat-seal baggies, plastic wrappings covered in duct tape and marked with numbers, two heat sealers, a large digital scale, an unidentified white powder, scraps of paper with Spanish words and lists of numerals written on them, seven cell phones,” and more than $50,000 in currency. He was charged with drug trafficking offenses. At trial, the trial court admitted the testimony of the agents as both expert and lay testimony. The agents provided expert opinion testimony that the defendant was engaging in counter-surveillance activities, some of the seized papers constituted drug ledgers, and some seized items were used in the drug trade. After his conviction, on appeal for the first time the defendant argued that the trial court improperly failed to give the jury cautionary instructions about the dual testimony of roles the agents played in their testimony and to make any clear demarcation between the agent’s expert and lay testimony.

The Sixth Circuit concluded that there was no error in admitting the agent’s expert testimony. However, a separate issue concerned the admission of dual expert and lay testimony by the agents. The circuit noted that it had “not categorically prohibited an officer from testifying as both a fact witness and an expert witness,” but “both the district court and the prosecutor should take care to assure that the jury is informed of the dual roles of a law enforcement officer as a fact witness and an expert witness, so that the jury can give proper weight to each type of testimony.” (quoting United States v. Thomas, 74 F.3d 676, 683 (6th Cir. 1996)) The circuit reviewed the issue for plain error since no objection had been raised at trial concerning the dual testimony. Plain error resulted by the trial court’s failure to clearly demark between the agents’ expert and lay testimony and failure to give a cautionary instruction about the dual roles of agent’s testimony. As the circuit explained:

“A general instruction on weighing officer testimony does not guard against a jury mistakenly weighing opinion testimony as if the opinion were fact, nor does it instruct the jury that they are free to reject the opinions given. Nor does such a general instruction regarding possible law enforcement bias address the additional risk of bias in forming expert conclusions regarding one's own investigation. Here, no instruction on expert witness testimony was given, let alone an instruction on the agents' dual role as fact and expert witnesses.”
Lopez-Medina, 461 F.3d at __. The circuit concluded that plain error resulted: “We conclude that permitting police officers to testify as experts in their own investigations and give opinion testimony on the significance of evidence they have collected, absent any cautionary instruction, threatens the fairness, integrity, and public reputation of judicial proceedings, regardless of whether the defendant is actually innocent.” Lopez-Medina, 461 F.3d at __.



The Lopez-Medina case serves as a reminder about the risks of using dual expert and lay testimony. Absent necessary precautions, reversal may result even where no trial objection is raised at trial.

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). Subscription information here.

Federal Rules of Evidence
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