Collin Yamauchi was an LAPD criminalist who performed PCR-based DNA testing and testified about evidence handling, testing procedures, and results, including blood samples from Simpson's Bronco. During direct examination by prosecutor Rockne Harmon, Yamauchi said news reports that Simpson was in Chicago had led him to expect an exclusion before testing; he testified that samples from the Bronco's driver's area were consistent with Simpson and that a center-console stain contained a mixture of Simpson and victim alleles. His testimony extended across multiple days of direct, cross, redirect, and recross examination, addressing his training and supervision, proficiency testing, laboratory protocols and documentation, the extraction of Simpson's reference blood in the same session, location, and timeframe as evidentiary samples, the vial's arrival unsealed contrary to written protocol, glove-changing, and an incorrect genotype in a mock study. Defense expert Dr. John Gerdes later criticized Yamauchi's handling of Simpson's reference sample alongside low-DNA evidence while discussing broader contamination problems in the LAPD laboratory.