reporter: he hadn t told you that? he hadn t told me that. that was in the first couple of weeks that i was dating him. reporter: sam emphatically denied any involvement in cathy s murder. but just the idea spooked tina. so she made up a lie. i met him and i told him that i was dating somebody else. reporter: which was not true? which was not true. reporter: you were a little freaked out by that? well, yeah. reporter: but the spark that drew her to sam was too strong, and though tina had only known him a few short weeks, something in her heart said sam was innocent. so i gave him a call. and i started dating him again. reporter: okay. i mean, you re an attractive woman. i have trouble believing that there were not guys available who weren t already suspects in a murder investigation. i m sure there probably were. but there they didn t have my attention. reporter: they dated for a year, and then married.
the microscopic calling card many of us leave behind just by putting our hands on something. if sam and javier did place cathy s body in the car s trunk, maybe, thought larry, there would be touch-dna on her clothes. search for dna in the areas that might be grabbed. especially areas that might be grabbed that don t have blood on them, from cathy. so you looked, what, on the ankles and under her arms? ankles, arms, i think under the legs. sometimes, you know, in the reporter: daron wyatt send out the evidence for touch dna. you optimistic? or are you thinking, shot in the dark? no, i was not optimistic. i was not optimistic. reporter: because what? because on this particular case, it seemed like for the beginning phases, everything that could go wrong pretty much went wrong. reporter: but he also knew he was working with a cop on a mission. daron wyatt was not going to quit until i filed this case or
about, are you serious? reporter: remember, cathy was seeing another guy. albert. who, only days later tried to kill himself. tina says cathy thought about sam s proposal all that week. ultimately, cathy decided, says tina, that she was so broken up about albert she was going to tell sam the answer was no. she s crying, and then she said, i m going to tell him this saturday that i m not gonna take off with him, that i will not elope. that was wednesday. and then saturday she never came home. reporter: sam s admitted jealousy, cathy s doting on albert, a rejected proposal. all of it seemed to add up to motive. but motives don t prove murder. there was still no physical evidence tying sam to the crime. all the blood on the car had been tested, and it was all cathy s. but then, while combing the case file, detective daron wyatt learned something shocking. there were blood and hair samples that had never been sent to the crime lab. and when those samples were analyzed, they pointe
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. rep
no, it didn t. because i had never seen her come home like that. and she couldn t tell me what had happened. reporter: she smell like alcohol? no, she didn t. that was that was the scary part to me that, you know, that she did not smell like alcohol, yet something was wrong with her. reporter: even more alarming, mary later realized cathy s underwear was missing. what you re describing is what happens when people come home after they ve been date raped. well, yes. reporter: you know, they can t remember what happened. they re maybe not wearing all their clothes and they are clearly under the influence of something. well, yes. i was afraid that maybe that had happened to her. but i didn t know for a fact. reporter: and she had no memory? and she had no memory. reporter: you think about