between 9:00 p.m. and 3:00 a.m. robinson was alone with his children during this time. >> carlos' wife was gone on the night this murder occurred. she was gone to visit a relative in a neighboring city. >> but investigators needed proof that carlos robinson was the killer after all and not just a neighbor who found her body and hadn't reported the crime. >> people often look for somebody that has a motive, and what we were trying to prove to the jury is that a person who barely knew the victim for four days had killed her and that the ex-boyfriend that was abusive to her didn't. >> then investigators discovered either another piece of evidence or a complication. in looking at the crime scene evidence, scientists noticed something in the hamburger buns. one of them was misshaped.