but he just seemed like, "what in the world's going on?" >> reporter: and despite the tension during the marriage and divorce, those who knew brooke best didn't think her ex-husband was a killer. >> i just never entertained that thought. >> clayton was a good person. so i didn't think that, you know, he would be capable of doing something like that to brooke. >> reporter: more importantly, clayton's alibi checked out. investigators cleared him. if not the ex-husband, then who? who had brooke come in contact with that weekend? investigators retraced brooke's steps, starting not with the game on saturday, but with the night before, friday. friends told investigators they had tickets to a concert. >> she was super excited about going to that. so she was just like, "okay, i've got to go -- i've got to go find something to wear. i'm going to go to dinner." >> reporter: after dinner, brooke left her car in a shopping center parking lot near