The plaintiffs presented blood evidence and chain-of-custody testimony from LAPD officials Gregory Matheson and Dennis Fung. Defense attorney Robert Blasier challenged the handling and documentation of that evidence, including the renumbering of Simpson's reference blood vial, the absence of tracking-system entries until June 16, the late identification of stains, Fung's descriptions of work physically performed by trainee Andrea Mazzola, and movement of the bagged Rockingham glove into the Bundy scene. Matheson offered explanations about evidence packaging and the difficulty of seeing blood on dark socks, while Fung defended his use of 'I' as referring to the mental aspect of collection. The questioning also advanced an explicit defense tampering theory concerning how blood could move between reference vials.

• Bernie Douroux's prior testimony (tow truck driver) was read in establishing that the Bronco was locked, left unattended for only three minutes, and showed no visible blood.
• Matheson explained conventional serology and, relying on a four-type profile supplied by Lambert for item 49, calculated a frequency of about .17 percent, or roughly 1 in 550-570 people; he said conditionally that Simpson would be in that group if he had the same four types.
• Blasier challenged the change to Simpson's reference blood vial item number from 18 to 17, arguing that it obscured when the vial was booked relative to other evidence; Matheson said he did not know why it was changed and defended the change as routine.
• Matheson acknowledged that none of the evidence collected on June 13-14 was entered into the LAPD tracking system until June 16, creating a chain-of-custody gap.
• Blasier questioned Fung about roughly 40 hours spent preparing with plaintiffs' counsel and challenged his grand jury use of 'I' for evidence physically collected by trainee Andrea Mazzola; Fung said he had been describing the mental aspect of collection.
• Matheson said blood on Simpson's dark socks was nearly invisible without laboratory lighting; on recross, he acknowledged that no one reported seeing blood until August 4, when a large ankle-area stain was identified.
• Fung was questioned about the shared item number 116 for a June 13 front-gate stain and a July 3 back-gate sample.