Dr. John Gerdes was a clinical laboratory director called by the defense to challenge the reliability of the LAPD crime lab's DNA evidence. Examined by Barry Scheck over multiple days in August 1995, Gerdes drew a sharp contrast between the rigorous, legally mandated standards of clinical laboratories — where errors could kill patients — and the lower, voluntary standards governing forensic labs like the LAPD's, testifying that the lab exhibited severe contamination problems. His testimony spanned four days of direct, cross, and redirect examination, with prosecutor George Clarke mounting an extensive cross-examination that forced concessions, including that RFLP results from independent laboratories were reliable and that Gerdes had no direct evidence of contamination in key samples.