OJ may be a free man because he was innocent. Read
Tainting evidence by John Kelly and Phillip Wearne.
By the way, Mullis never testified at OJ's trial. Yes, his PCR technique was used, but the primary flaws in the DNA technology were the fault of the FBI and the LA police who almost certainly falsified evidence. I don't see how you can accuse Mullis of having any significant impact on the outcome.
Although he didnt testify, we had to hear on and on from Johnie Cockroach about how they had a "Nobel Peace Prize" winner (cockroach was too stupid to recall that Mullis was a Chemistry Nobel Laureate) to testify on how "disputable" the evidence was. I followed that case very, very closely (Im a trained Ph.D. Molecular Biologist, who lived in L.A at the time) and OJ was a guilty as you can get.