didn't you slap me when i put that song in? it had nothing to do with carrie. it was just a song. >> but to prosecutors it was more than a song. a look inside the mind of a killer and they were determined to prove that in court. tim mcvay was about to stand trial for murder. >> and he was about to face a showdown in court one boyfriend accusing another on the stand. coming up. >> the way she stormed out of the door i thought maybe i upset her. >> what really happened to carrie, when "dateline" continues. r. so go to carvana and enter your license plate answer a few questions. and our techno wizardry calculates your car's value and gives you a real offer in seconds. when you're ready, we'll come to you, pay you on the spot and pick up your car, that's it. so ditch the old way of selling your car,