>> reporter: before tom kolman? >> before tom kolman. >> reporter: same day? >> same day.this person and said, "kind of always thought that was a sterile environment." and she said, "well, you should give that a check." so, we did. >> reporter: sure enough they got a match. turns out the d-n-a belonged to the deceased male who'd been on the medical examiner's table before tom. so the d-n-a had nothing to do with the case, but it did mean that some evidence had been contaminated. >> reporter: what are you thinking when you hear that? >> well, i'm thinking a couple things. i'm thinking, "that's gonna be a problem at trial because of the contamination." but i'm also thinking, "thank god, we get a little break. >> reporter: and after all the additional testing, the medical examiner finally had a cause of death, acute midazolam poisoning. investigators took everything they had to a special prosecutor and argued they were sure gilberto nunez had killed the man he called his best friend. >> i don't think that nunez was ever a friend to kolman. not for a minute do i believe that.