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4.15 Dual Role Testimony

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You [have heard] [are about to hear] testimony from [name] who [testified] [will testify] to both facts and opinions and the reasons for [his] [her] opinions. 

Fact testimony is based on what the witness saw, heard or did. Opinion testimony is based on the education or experience of the witness. 

As to the testimony about facts, it is your job to decide which testimony to believe and which testimony not to believe. You may believe everything a witness says, or part of it, or none of it. [Take into account the factors discussed earlier in these instructions that were provided to assist you in weighing the credibility of witnesses.] 

As to the testimony about the witness's opinions, this opinion testimony is allowed because of the education or experience of this witness. Opinion testimony should be judged like any other testimony. You may accept all of it, part of it, or none of it. You should give it as much weight as you think it deserves, considering the witness's education and experience, the reasons given for the opinion, and all the other evidence in the case. 


If a witness testifies to both facts and opinions, a cautionary instruction on the dual role of such a witness must be given. This situation can arise, for example, when a law enforcement witness testifies as both a fact witness and as an opinion witness. See United States v. Torralba-Mendia, 784 F.3d 652, 659 (9th Cir. 2015); United States v. Vera, 770 F.3d 1232, 1246 (9th Cir. 2014). In a criminal case, omitting such a cautionary or curative instruction is plain error, even if no party requests such an instruction or affirmatively opposes it. See Vera, 770 F.3d 1232 at 1246 (holding that court’s failure to instruct jury on how to evaluate agent’s dual role testimony prejudiced defendant when agent testified as both expert witness and lay, or fact, witness); see also Torralba-Mendia, 784 F.3d at 659 (noting holding in Vera and finding error in district court’s omission of dual role instruction differentiating between lay and expert testimony). Indeed, in Torralba-Mendia, the government proposed such an instruction, the defendant objected, and the court declined to give the instruction; the Ninth Circuit found plain error. Id

The court might also consider bifurcating a witness’s testimony, separating a witness’s percipient, or factual, testimony from the witness’s expert opinions. See United States v. Anchrum, 590 F.3d 795, 803-04 (9th Cir. 2009) (holding that district court "avoided blurring the distinction between [the case agent’s] distinct role as a lay witness and his role as an expert witness" when it "clearly separated [the agent’s] testimony into a first ‘phase’ consisting of his percipient observations, and a second ‘phase’ consisting of his credentials in the field of drug trafficking and expert testimony regarding the modus operandi of drug traffickers"). 

In addition, if an opinion witness is allowed to present otherwise inadmissible evidence under Fed. R. Evid. 703, an additional instruction may be needed. See Comment to Instruction 4.14. Also, when an opinion witness presents both expert opinion testimony and lay opinion testimony, as happened in Vera, further instructions may be needed. 



Approved 3/2018