it showed david swann, just as he said it would. >> we were able to verify through the atm tapes, david swann did not have the window of opportunity to commit this crime. >> with david swann cleared, there were no other suspects. investigators feared that karyn slover's murder might never be solved. >> i took it personally. i spent a lot of sleepless nights thinking about this case, wondering what i was missing, what we weren't doing, what we needed to do to actually come up with a killer in this case. >> as a last resort, police looked one more time at the crime scene. it was clear, there had to be another car at the scene. >> there had to be more than one person involved in this. you couldn't leave a vehicle along the interstate and walk back to wherever you left from. someone had to drive there and pick you up and take you back. >> so, who would have had the motive and the opportunity to commit this crime? karyn's ex-husband, michael, had an alibi for the night of the murder, but his parents did not. they were the ones watching karyn's son, christopher, on the day of the murder. >> m