we just don't know. >> reporter: of course, david had been on edmunds' radar from the moment investigators first met him outside kay's hospital room and thought he was acting strange. >> i knew there was something there. i just couldn't -- just couldn't figure out what yet. >> reporter: but after finding out about his affair with becky and hearing that becky could be behind the murder, edmunds called david in for his first formal interview and got it on tape. >> what i need you to do is tell me about your relationship with becky. >> okay. >> reporter: david came clean he admitted to being an unfaithful husband to kay and explained how it all began. >> we had been playin' tennis. you know, workin' out. the four of us. we would go play it would actually be becky and i against her and tony. one day she -- she said, "you know why i suck so bad at tennis is 'cause you distract me out there." you know, kind of, you know, a little flirt thing goin' on. >> reporter: a flirty game of mixed doubles that turned into a hot and heavy affair between next door neighbors.