tough. >> reporter: but what really made this case a prosecutor's nightmare was the fact that all the physical evidence pointed away from the man they thought was the killer. any defense attorney would ask, if police found javier's dna and fingerprint, why would they charge sam? were you surprised you didn't find sam's dna there? >> yes. >> reporter: he thought newer, better tests might find sam's dna, but it was too late for that. cathy's family had sold the car. the case against sam would have to be entirely circumstantial. murphy felt the key to that was somewhere in those interviews sam gave to police. but here, too, there was a problem. >> when you look at the interview, everything that sam lopez said seemed logical at the time. and everything seemed to make sense. >> reporter: picking apart those interviews would be critical. >> this is one of those cases where you have to look at the details. and it's truly one that you have to look at each detail in light of every other detail. >> reporter: and when you rearrange the letters of "little