There are many forms of impeachment, but can an expert witnesses be used solely to impeach a witness’s credibility? The Court of Appeals recently considered it.
Burrows v. Riley concerned a motor vehicle accident in a gas station parking lot. The district court granted Riley’s motion to exclude Burrows’ “accident reconstruction expert, William N. Morrison, finding that Morrison’s testimony would not assist the jury.”
The Court of Appeals affirmed, concluding the opinions offered “would not have assisted the jury, were speculative and conjectural, and would have improperly invaded the jury’s province.” Why? “Morrison did not conduct any experiments, calculations, or any other specialized analysis that resulted in information beyond a jury’s common knowledge.” Apparently Morrison also created a demonstrative video that was also excluded. Why? “[H]e did not know Bywaters’ height when he created the demonstrative video purporting to show her line of sight.” This demonstrative video to impeach a witness’s testimony itself was also inadmissible. It was beyond the permissible scope of expert testimony because it “inappropriately challenged Bywaters’ credibility by concluding that “her line of sight was obscured as she  testified to.” Specifically, this proposed testimony would have improperly invaded the jury’s province by effectively telling (and showing) the jury that Bywaters could not have seen what she says she saw.”
Could facts be used to impeach the witness’s credibility about what she saw? Yes. Could the party use an expert to impeach her? Not in this circumstance.
 No. 71350, 2018 Nev. App. Unpub. LEXIS 15, 2018 WL 565431 (Ct. App. January 19, 2018).