DNA evidence is often at the top of the discussion whenever I debate the Central Park five case. People think that Reyes’ DNA evidence proves them innocent. However, listening to their testimony you understand that none of them penetrated her and that any of the DNA evidence from the 5 that they would have found would have been on her person and not inside of her.
On top of that, the technology for gathering DNA evidence was in its infancy in 1989. Gathering trace (small amounts) evidence was extremely difficult.
Moreover, as these clips of the paramedic’s courtroom testimony show, Patricia Meili had been thrashing around in 2 inches muddy water for about 4 hours. It doesn’t take a rocket scientist to figure out that lots of trace evidence were probably washed away within those hours.