were in high school, lived across the street. cathy s older sister was married to sam s older brother. reporter: they had this long on again/off again relationship in which what, he couldn t let go of her or she couldn t let go of him? i think a lot of it was mutual. reporter: even after cathy started dating albert and sam had another girlfriend, too, they continued to see each other. and daron found evidence that in sam s mind, his relationship with cathy was far from casual. mary gave me a shoe box full of letters that were written between sam and cathy, and the content of these letters showed a very jealous guy. a guy who would get angry any time somebody flirted with cathy. reporter: sam didn t try to hide the fact that he was prone to jealousy. she knows, every time she mentions some guy s name, i get pissed off, okay?
shift brought him to this park just across the street from where cathy had grown up. daron was about to bust a drug suspect when the guy started talking. he s playing the game of, you know, i ll tell you whatever you want to know, just you know, ask the right questions and i ll tell you and then you won t take me to jail. so, you know, just almost as a flippant remark, i tell him, okay, so tell me who killed cathy torrez. reporter: it was a shot in the dark. a tactic he d picked up at a seminar for cultivating informants. and the patrol officer that is next to me starts kind of kicking my foot. and he s got an explorer scout who s riding with him a young hispanic female. and i look at her name tag and it was d. torrez. turned out it was debbie torrez, cathy s youngest sister. reporter: who just heard you ask that question. correct. reporter: you had no idea it was her? i had no idea. reporter: debbie torrez cathy s baby sister was now 14 years old. eager, he
reporter: daron went deeper into sam and cathy s relationship. there were a lot of things that brought them together, they were in high school, lived across the street. cathy s older sister was married to sam s older brother. reporter: they had this long on again/off again relationship in which what, he couldn t let go of her or she couldn t let go of him? i think a lot of it was mutual. reporter: even after cathy started dating albert and sam had another girlfriend, too, they continued to see each other. and daron found evidence that in sam s mind, his relationship with cathy was far from casual. mary gave me a shoe box full of letters that were written between sam and cathy, and the content of these letters showed a very jealous guy. a guy who would get angry any time somebody flirted with cathy. reporter: sam didn t try to hide the fact that he was prone to jealousy. she knows, every time she mentions some guy s name, i get
kicking my foot. and he s got an explorer scout who s riding with him a young hispanic female. and i look at her name tag and it was d. torrez. turned out it was debbie torrez, cathy s youngest sister. reporter: who just heard you ask that question. correct. reporter: you had no idea it was her? i had no idea. reporter: debbie torrez cathy s baby sister was now 14 years old. eager, her mom says, to assist police because of everything her family had been through. she remembered that when we needed help, people came to help us. so she thought it was her turn to help others. reporter: which is why debbie was in the park that afternoon, and how she heard daron mention cathy s case. that is a weird coincidence. we don t believe in coincidences. reporter: to daron wyatt, it felt more like fate. and just months later, in january 1997, his lieutenant suggested daron apply to the
second interview, the day cathy s body was found. detective wyatt studied that tape, too. there was one thing that was important that sam didn t display that you would expect to see in a case like this. reporter: which is? emotion. he showed more emotion over the contents of a coke can. he picked it up when they left the room and reading the coke can and the ingredients and the number of calories. and at one point he puts that down and picks up a baseball hat he had been wearing, sees dirt and brushes it off and starts swearing about the fact that there s dirt on his hat. oh [ bleep ]. but he never shows any emotion about the fact that this gal has been brutally murdered, no emotion whatsoever. reporter: and that s a big red flag? huge. reporter: daron went deeper into sam and cathy s relationship. there were a lot of things that brought them together, they were in high school, lived across the street. cathy s older sister was married to sam s older brother. reporte