William Thompson served as a defense DNA expert and UC Irvine professor who played a central role in the defense's challenge to the prosecution's genetic evidence. He was deeply embedded in the DNA phase of the trial, arguing motions on DNA evidence admissibility and the statistical methods used to interpret DNA mixtures. Thompson personally examined and cross-examined key population genetics witnesses, including Dr. Bruce Weir and Drs. William and Renee Shields, pressing on the reliability of the statistical frameworks underpinning the prosecution's DNA conclusions. His work spanned months of proceedings from early pre-trial motions through the heart of the defense case, making him one of the most active figures in the battle over whether — and how — DNA evidence would reach the jury.