Defense DNA expert Dr. John Gerdes testified that the LAPD DNA laboratory had persistent contamination problems, including contamination in two of four June 1993 runs and 10 of 25 extraction controls during May–July 1994, along with procedural practices he said created substantial cross-contamination risks. He criticized Yamauchi's handling of Simpson's reference sample alongside low-DNA evidence and the lab's failure to change gloves or laboratory paper between samples, and he challenged the treatment of a 1.3 signal in Bronco console item 31 after a control failure. Judge Ito sustained several foundation objections that prevented Gerdes from opining directly on the reliability of specific evidence results and struck his inference that a dated chelex bottle showed months-long reuse.

• Judge Ito overruled the prosecution's objection to Dr. Gerdes's contamination charts; Gerdes later testified that two of four June 1993 runs showed contamination
• Gerdes testified LAPD had the worst contamination levels of any forensic lab he reviewed, stating accrediting bodies would have shut it down
• Gerdes presented data showing 10 of 25 extraction controls contaminated during May–July 1994 testing period and five typing errors in LAPD validation studies
• Gerdes testified that Yamauchi's June 14th processing of high-DNA reference blood sample alongside low-DNA evidence swatches created unacceptable cross-contamination risk
• Gerdes contradicted LAPD criminalists Yamauchi and Matheson about lab equipment type, revealing the ventilation hood was chemical, not laminar flow
• Gerdes testified that LAPD failed to change gloves or laboratory paper between samples and handled as many as 20 samples in a single session
• Gerdes testified that a failed control meant the 1.3 signal in Bronco console item 31 could not be called a real allele, and he described DOJ's treatment of item 31 and item 52 as scientifically inconsistent
• Gerdes testified that unexpected alleles in Nicole Brown Simpson's and Ron Goldman's reference samples were consistent with cross-contamination from Simpson's blood during Yamauchi's June 15 handling session