DNA expert Gary Sims endured intense cross-examination by defense attorney Barry Scheck focused on challenging the integrity of DNA evidence from the crime scene and Bronco. A central battleground was the absence of bacterial degradation in rear-gate samples 115, 116, and 117 collected July 3, contrasted with degradation discussed for item 50, item 51, and the handrail sample; the defense argued that the rear-gate environment could accelerate degradation, while the prosecution elicited that this did not exclude the stains having been present since June 13. The prosecution repeatedly redirected to rehabilitate Sims' testimony through technical explanations of contamination safeguards and evidence conditions.

• Barry Scheck conducted multiple cycles of recross-examination attacking DNA evidence collection integrity and procedures
• Defense contrasted degradation in item 50, item 51, and the handrail sample with its absence in the July 3 rear-gate samples, while arguing that the rear-gate environment could accelerate degradation
• Prosecution repeatedly rehabilitated Sims' testimony with technical explanations of contamination safeguards and environmental and storage conditions affecting bacterial degradation
• Sidebar dispute erupted over hearsay regarding Greg Matheson's prior knowledge of LAPD serology testing on the sock
• Defense introduced handwritten examination notes documenting glove cutting G1-G4 collection procedures