josh mankiewicz: with that information, a producer from kfmb went to the home where dennis lived withents. reporter: where was he the night of the murder? he was right here. reporter: didn't he have a date with her that night? woman: shut the door! [door slam] josh mankiewicz: and the police come to see you, lieutenant rooney. - mm-hmm. josh mankiewicz: and you're thinking, what, he's going to give you a big thank you. uh-huh. and what did you get instead? very angry. josh mankiewicz: and you were not happy. no. no. not at all. i said, i can't have these details out there, and if it means, i don't tell you another thing until this thing is resolved one way or another, that's what i'll do. because my obligation is to your daughter and her son. did she understand that? i think she did. josh mankiewicz: they hadn't solved the case, but rooney's crime lab did solve one issue. dayna had been right. that a test ordered by police or the courts would come out differently. dennis potts' dna proved he was the father of baby dean, and his dna didn't match the dna sample that had been sent to the