sam lockhart, the uncle was playing ball that night too.could have slipped away? >> is it possible that he snuck out, was gone 10 or 15 minutes, killed his family and snuck back in without any one of us noticing it? absolutely not. that's impossible. >> but if david wasn't the killer, then who was? the defense had its answer. it was the person who owned that gray sweatshirt. the one that was lying by brad's body on the garage floor the night of the murders. defense attorney, mike mcdaniel, had recognized the sweatshirt as prison issue. >> in the collar of the sweatshirt is the word, "backbone." and i'm thinking, "okay. that's a nickname." >> tests on that sweatshirt revealed dna from various people, including an unknown male. but the prosecutor said there was no match when that male dna was run through the national database. still it seemed to be a breakthrough for team david. proof that someone else was in the garage that night. >> we knew that that was probably the key to solving this. now, we didn't know that person by name. by god, we k