was murdered. one thing for sure, it was not steve. >> we exhausted so many man hours and looked at any and all alternatives. >> reporter: and then it was during the long months of waiting for a new trial to begin, the prosecution had an idea. what if that 603 sample was a simple mistake. what if something just got mixed up in the lab? so investigator mike sechez looked up the autopsy done just before carol's. and submitted a sample from that for re-testing. and? nearly three years after carol's murder, a call from the crime lab. >> the sample dna that we sent had matched the dna under carol kennedy's fingernails. we finally were able to discover and verify who mr. 603 is. >> reporter: mr. 603, it turned out, was another dead soul, the man lying on the autopsy table before carol got there. it was his dna. maybe on one of the coroner's instruments, that ended up under carol's fingernails.