Defense forensic toxicologist Dr. Fredric Rieders testified that EDTA—the anticoagulant preservative found in blood collection tubes—was detected in evidence from Nicole Brown Simpson's back gate and the defendant's sock, supporting the defense theory that blood was planted from preserved samples. Rieders testified that EDTA levels were approximately 1,000 times higher than dietary sources could produce and opined that the most likely source was a purple-topped blood collection tube. Prosecutor Marcia Clark launched a vigorous cross-examination, focusing on a possible typo in an EPA source, Agent Martz's unpreserved blood producing similar EDTA characteristics, and the Sconce case, where a later expert did not replicate Rieders' finding on the same tissue. The court excluded photodegradation evidence lacking scientific foundation and particular dietary EDTA materials on relevance and discovery grounds, while allowing reference to previously disclosed EPA materials.

• Court allowed Dr. Rieders' EDTA testimony despite prosecution's exclusion motion.
• Rieders testified EDTA was present in sock (Q206) and back gate (Q204) evidence.
• Rieders criticized FBI's EDTA testing methodology for lacking internal standards and validation studies.
• Court excluded photodegradation evidence for insufficient scientific foundation and excluded specific dietary EDTA materials on relevance and discovery grounds, while allowing reference to previously disclosed EPA materials.
• Rieders testified EDTA levels were roughly 1,000 times higher than diet alone could produce.
• Clark exposed potential typo in EPA report Rieders relied upon during cross-examination.
• Clark elicited damaging admission that FBI Agent Martz's own unpreserved blood showed similar EDTA levels.
• Clark questioned Rieders about the Sconce poisoning case, eliciting that a later expert did not replicate his oleandrin finding on the same tissue.
• Judge issued stern warning to Clark for editorial commentary during cross-examination.
• Court negotiated early Friday 8:30 AM start to accommodate Rieders' medical appointment and Vienna trip.