Collin Yamauchi was an LAPD criminalist who performed PCR-based DNA testing on key evidence in the case, including blood samples from Simpson's Bronco. Presented by prosecutor Rockne Harmon over extensive direct examination, Yamauchi walked the jury through testing procedures and results—but his testimony became a focal point for the defense when he admitted he had expected Simpson to be excluded based on news reports, raising questions about examiner bias. Barry Scheck subjected Yamauchi to one of the trial's most extended cross-examinations, exposing his limited experience, the lab's lack of proper supervision, and critical procedural lapses: the reference blood sample had been extracted alongside evidentiary samples, the blood vial arrived unsealed, and Yamauchi had processed evidence while wearing blood-stained gloves just feet from Simpson's reference vial. His testimony spanned multiple days of direct, cross, redirect, and recross examination, and the contamination concerns Scheck raised through him became a cornerstone of the defense's broader attack on LAPD lab credibility—later reinforced by defense expert Dr. John Gerdes, who called the lab the worst he had ever observed.