>> he had done some jail time. >> back in fwo2002, a 18, sam herr was charged in the murder of another teenager. he was acquitted, but sam's dad knew that in hindsight, it didn't look good. >> didn't buy you a lot of rhythm from law enforcement. >> no, and i understood that. that's why it was imperative to start looking immediately. >> steve wanted to find his son to prove he was innocent. orange county prosecutor matt murphy also wanted to find sam quickly, for an entirely different reason. >> you've got a dead woman in his apartment, he's missing, and then you factor in afghanistan and you start thinking, okay, he's a trained killer. he had been accused of this before and you think this guy is potentially very dangerous. >> the detectives and the dad hunted sam independently. but on parallel tracks. detectives spoke with sam's neighbors. >> i saw sam that day and had a short conversation with sam. >> rachel and dan said sam was