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>> i was at school and she paged me eight times in a row. >> reporter: mary, however, says sam was the one calling her home looking for cathy. >> he called how many times? >> quite a few times looking for her. >> reporter: mary says sam sounded okay at first, until she told him where cathy was. >> i said she was at the hospital and she wasn't back yet. >> reporter: at the hospital, visiting albert, her boyfriend who'd attempted suicide. >> sam okay with that? >> no, he got upset. >> reporter: sam told police he was just worried about cathy, especially after he spoke with her that week. >> she was crying on the phone saying, like, you know, "i messed up," you know? "i never tried getting him hurt," and all this stuff. and i told her, "you know what, just calm down, you know, 'cause when you're depressed you do dumb things." >> reporter: remember, this interview happened while cathy was still missing. sam seemed to be implying she might have hurt herself. or that another boyfriend might be involved. >> i mean, look, she -- she's had -- i know she's had a lot of

problems in the past with boyfriends. >> reporter: then there was 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. >> which is? >> emotion. >> he showed more emotion over the contents of the coke can. he picked it up when they left the room. and he's reading the coke can and ingredients and the number of calories. and then at one point, he puts that down and he picks up a baseball hat that he had been wearing and he sees some dirt on it and he brushes it off and he starts swearing about the fact that there's dirt on his hat. >> oh [ bleep ] >> but he never shows any emotion about the fact that his gal has been brutally murdered. no emotion whatsoever. >> and that's a big red flag. >> it's huge. >> reporter: daron went deeper into sam and cathy's relationship. >> there were a lot of things that brought them together. they had dated in high school, they lived across the street. cathy's older sister was married to sam's older brother.

>> 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 -- 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, ok? >> reporter: that led the detective to take a fresh look at those bizarre events the week before cathy disappeared when she came home impaired and then had her tires slashed.

>> she never regained full memory of what had happened but she was able to tell everybody who she had been with that night. >> reporter: the person cathy had been with that night? sam lopez. when police asked sam about that night, he remembered something very specific. >> a hickey. >> on her neck? >> on her -- right here. covered up with her bra. >> you mean way down here on her shoulder? >> right here. right here. >> reporter: sam claimed it was no big deal. >> i didn't want to hit her up, like, tell her: "hey, you know, who were you with last night?" whatever. >> reporter: but that night, police records showed sam received two traffic citations, both while driving cathy's car. one was an open container ticket for drinking alcohol in a parking lot. the other for failing to stop at a stop sign. the cop who pulled sam over for not stopping, said sam flew thru the intersection, and when he approached the car, the cop said it looked as if sam and cathy had been arguing. but he did say cathy looked

fine. nobody was quite sure what happened after that, except they apparently parted company. sam in his car, cathy in hers. then cathy arrived home, too out of it to realize she'd been driving on slashed tires. tina saw the tires the next day. >> i just kept saying, "who -- what happened to your tires? who slashed your tires?" >> and she -- and she'd say? >> and she'd say she didn't know. she -- she just knew that she had gone out with sam that night. >> reporter: daron wyatt now believed sam drugged cathy, possibly assaulted her, and slashed her tires. the next day, cathy called tina with more details about her strange night with sam. >> he had told her "let's run off, let's get married. let's run off and let's elope." and she told him, "are you --" you know, "you're joking, you're," you know, "this is not," you know, "what are you talking 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 gonna 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 pointed to a whole new suspect.

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>> reporter: back in 1994, police suspected sam lopez of killing his sometime girlfriend, cathy torrez, but they couldn't make the case. one big reason -- sam's cousin, xavier, who told detectives he was with sam the night of the murder. xavier was sam's alibi. so he wasn't suspected of being part of the murder, or even being at the crime scene. >> that's right, yeah. they were looking at xavier solely as an alibi witness who was lying to cover for sam. >> reporter: that's why, as detective daron wyatt now discovered, even though

investigators in 1994 took blood, hair and fingerprint samples from xavier, they'd never had those tested. >> they had sent all of the evidence related to sam lopez to the crime lab, his fingerprints, his hair, his blood. but they hadn't sent anything related to xavier lopez to the crime lab. >> reporter: daron sent xavier's samples, now three years old, to the crime lab. two months later, the phone rang. >> they had positively identified a fingerprint on the trunk of cathy's car, left there by somebody closing the lid of the trunk. >> reporter: xavier's print was on the trunk of cathy's car? >> yes. >> reporter: weeks later, another call from the lab. a bloodstain on the car had tested positive for both cathy's dna and xavier's. and the detective found there was something else -- another major piece of evidence investigors had initially overlooked. >> when you look at the crime scene photos in the trunk of the car, something jumped out at me.

and it just -- it hit me like i got punched in the face, was there was arterial spurt on the sidewall of the trunk panel. >> reporter: meaning only one thing -- cathy was still alive when she was placed in the trunk of the car. so, if xavier put her there, he could be charged with murder. why not grab xavier up that day and say, "okay, your dna and fingerprints were at the scene. we didn't know that until just now. you're going away for murder unless you start talking."? >> well, let's say that we did that and we bring him in and he says, "well, yes, my fingerprint was there because i helped her push her car out of the street a week before. or when i was helping her change a tire. i cut my finger and i bled on it." >> reporter: so instead of approaching xavier, daron wyatt spent nearly five months carefully watching him and sam. he learned the two cousins were unusually close. >> sam lived in a one-bedroom little bungalow with his wife and his baby at the time, yet xavier was there all the time,

sleeping in the same -- essentially the same room. >> reporter: eventually, daron wyatt felt he had enough new information to get a search warrant. >> there was a loud pounding on our door. >> reporter: tina montelongo remembers it clearly. >> when i opened the door, there was about five police officers there. the one in the middle was wyatt. he put us against the wall and patted us down. >> reporter: what was sam's demeanor while all that was happening? >> he was calm, you know. he really was. i was freaking out. >> reporter: he wasn't worried? >> no. no. >> reporter: maybe he had no reason to be. police didn't find anything in the house linking sam to cathy's murder. they even sprayed his truck with luminol looking for signs of blood. >> we took the seats out, we did everything we could. and there was nothing. >> reporter: police briefly detained sam, but he was back home by morning. now daron wyatt focused on xavier.

>> and we really approached it very low key. "we think that you can really provide some great information for us. would you mind coming down with us and talking." >> reporter: they brought him down to the station and listened patiently as he distanced himself from cathy torrez. >> he'd never been shopping with her, never changed a tire on her car, never carried groceries. we went through the whole litany of things that -- >> reporter: and he's all, "oh no, no, that's --" >> would -- >> reporter: that's all true. "i'm a million miles away from her"? >> right, right separated himself. >> reporter: but in so doing, xavier ruled out any innocent explanation for finding his dna and fingerprint on her car. so when police told him that's exactly what they had found -- >> it was like vapor lock. and then all of a sudden he said, "well, you know, this one time i was at the video store, and i saw sam and cathy there together. and i went and i sat in cathy's car and sat in the backseat and waited for them. and they came out and then i left."

and that was really his only contact that he could give us with cathy's car. >> reporter: but he doesn't fold up like a house of cards and say, "all right, fine. you got me." >> you're right. but josh, you've watched probably thousands of these interviews. and sometimes what people don't say is just as important as what they do say. >> reporter: what xavier either would not or could not say were these words -- "i did not kill cathy torrez." >> he says, "i don't know who did." "that's not what i asked, xavier. did you kill cathy torrez?" "i don't know who did." and we play that several times to where he'd finally say, "i didn't do it." "you didn't do what, xavier?" "i didn't do what you say i did." >> reporter: can't say the words, "killed cathy"? >> correct. then it moved to, "did you put cathy's body in the trunk of the car?" "i don't know who did." finally he sat there and he put his fist in front of his mouth to keep himself from talking. >> reporter: but xavier had already managed to talk his way into an arrest for murder.

nearly four years after cathy's death, he was booked into the orange county jail. cathy's family was stunned when they heard the news. tina included. remember, she was still married to armando, who was sam's brother and xavier's cousin. >> yes. that -- that was a shock. that was a shock. >> reporter: you didn't see that coming and police didn't tell you? >> right. that was part of their investigation, and we had no knowledge of that. >> reporter: but they were relieved. at last the case was moving forward. daron wyatt was confident he had enough evidence to prove xavier lopez had killed cathy torrez. but once again, the orange county district attorney did not agree. the d.a. decided not to charge? >> correct. >> reporter: and so xavier's set free? >> xavier walks. coming up -- >> a detective who refuse toss quit. >> i said i've got a cold case

that i need to you take a look at. >> now has another good reason not to. >> my first daughter was born and i remember going to mary shortly after that and saying i know, i know now how you feel. >> when "dateline" continues. ♪ ♪ protect your pet with the #1 name in flea and tick protection. frontline plus. trusted by vets for nearly 20 years.

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i'm dara brown. a 20-page secret letter to special counsel robert mueller arguing that the president cannot be forced to testify in a russia meddling investigation. they argued trump cannot be -- he has absolute authority over all federal investigations. a stew length-led group held demonstrations across the country on saturday against gun violence. now back to "dateline." >> reporter: detective daron wyatt never believed xavier lopez acted alone.

even when he arrested xavier in 1997 for the murder of cathy torrez, he thought xavier's real role was helping the prime suspect -- xavier's cousin sam lopez. tina montelongo, sam's then-wife and xavier's friend, wasn't buying it. can you conceive of xavier going through with a murder or being involved in it because of his loyalty to sam? >> no. i don't see that if sam did it, would xavi help him just because they're close family? i don't see that. >> reporter: neither did the d.a. who decided there was not enough evidence to file charges. how do you tell mary bennett, "we had xavier, but we had to let him go?" >> it was extremely difficult. there was a lot of crying on both sides. >> reporter: daron knew exactly what releasing xavier really meant. what walks out of the jail along

with xavier is any leverage you had to get him to name sam? >> yeah, absolutely. >> reporter: and now you really are back to square one? >> yes. >> reporter: is that the end? >> to some people. >> reporter: but not to him. and not to mary. you put a lot of faith in daron. >> i put a lot of faith in god. daron was his tool. >> reporter: but for the time being, it seemed daron's hands were tied. after all, the case had been rejected by the d.a.'s office twice before. this case getting a lot of baggage over the years? >> yeah, it did. >> reporter: and so if you go ahead with it, you're not only going ahead with the case, you're also kind of insulting the d.a.? >> yeah. >> reporter: years went by. the cathy torrez case grew colder by the day. and so did the marriage between cathy's sister tina and sam's brother armando. you and armando got divorced. >> yes. >> reporter: this have something

to do with that? >> no. definitely it was all intermixed. >> reporter: daron wyatt was promoted to detective sergeant and his caseload shifted to other types of crime. but he never forgot his promise to mary. in part because of a milestone in his own life. >> my first daughter was born. and i remember going to mary shortly after that and looking her in the eye and saying, "i know -- i know now how you feel. i know it. i can feel it myself. i'm a dad now. you haven't given up. i won't give up." >> reporter: in 2003, nine years after the murder, daron once again approached a friend in the d.a.'s office. >> i said, "i've got a cold case that i need you to take a look at." and he physically stops walking and he says, "if it's the case i'm thinking about, i'm not gonna touch it. >> reporter: but daron was persistent. eventually he persuaded his friend to take cathy's case back to the d.a.'s homicide unit. the same unit that had rejected

it twice before. this time though, something different happened. a prosecutor unfamiliar with the case agreed to take a fresh look. his name is matt murphy, and he noticed one thing right away. >> the first thing you see when you look at the file is a big rejection from really good lawyers who reviewed it individually and as a group. >> reporter: which means they tried very hard to make a case and they couldn't do it? >> they tried very hard. that's right. and they figured, based on their review, that they couldn't do it. >> reporter: and some of the reasons were apparent from the get go -- >> when you look at it on its face, this case is a real tough one. >> reporter: for one thing, there was so much evidence they didn't have against sam. >> there was no murder weapon here. we had no witness. we had no confession. we had no dna. so, you can look at it that way, in a conventional review. and, yeah, it looked really 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 xavier'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 tiny details," it spells "larry montgomery." >> absolutely. >> reporter: larry montgomery. or as he's known here at "dateline," the evidence whisperer. coming up -- >> a human lie detector goes to work. >> a guilty person knows a lot. all that information is in his brain and it can slip out. >> when "dateline" continues. protect your pet with the #1 name in flea and tick protection. frontline plus. trusted by vets for nearly 20 years. you could start your search at the all-new carfax.com that might help. show me the carfax? now the car you want and the history you need are easy to find. show me used minivans with no reported accidents. boom.

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happiness is powerful flea and tick protection from nexgard. nexgard kills fleas and ticks all month long. and it comes in an easy-to-give tasty chew. and that makes dogs and owners happy. no wonder vets love it too. reported side effects include vomiting, itching, diarrhea, lethargy andack of appete. see your vet for more information on flea and tick protection you and your dog will love. nexgard. the vet's #1 choice. >> reporter: prosecutor matt murphy thought daron wyatt's investigation of cathy torrez' murder was compelling. but he knew that making the case against sam lopez wouldn't be easy. the d.a.'s office had declined to try it twice before. so murphy called for help from a detective whose legendary skill with cold cases has earned him a

reverential nickname. >> larry montgomery is the real deal. i mean, the guy is -- the evidence whisperer. i mean another name for him is saint larry. >> larry sees things other people don't see? >> larry sees things that many people don't see, yeah. and he looks at it from a different perspective. >> reporter: they both felt the key to the case lay in sam lopez's own words his taped interviews with the original detectives. and they thought the perfect man to listen to those interviews was the evidence whisperer. >> guilty people have tells, just like in a poker game? >> absolutely. they don't have that innocent mindset, and they -- they have other fears. they fear being caught, they fear lying in a way they -- they can't get their stories straight because there's too many details. >> reporter: montgomery spent months carefully listening and re-listening, watching and re-watching, hours of sam's interviews. looking for the tells. >> how long have you guys been dating? >> it's -- it's an off -- on and

on thing. on-and-off thing. >> okay. >> reporter: tell number one how sam talked about his relationship with cathy. >> see, i was going out with somebody. and then she would call me up. and we would just, like -- calling each other, going out to eat, places like that. nothing serious at the time. >> sam definitely was trying to limit his connection with cathy, give the impression that it's not that big of a deal. >> reporter: remember cathy's sister tina had told detectives sam had proposed to cathy just days before she disappeared. but when police asked sam about that, he denied it. >> you didn't ask her to marry you, then? >> no. >> reporter: later he changed his story but seemed to say getting married was cathy's idea. >> a lot of people hit me up already. they said that -- that -- that we were supposed to elope, ok? >> this is what she -- okay, but look. she had a crazy idea to go to mexico, okay? just the two of us. >> reporter: then there was sam's claim that cathy never

tried to contact him after she disappeared. >> i thought she was gonna page me on friday. she goes somewhere, and she never paged me on friday. >> we know that cathy's mom paged him 20 or 25 times in a matter of at least a couple of days, trying to get him to contact her because he's so close to cathy and she's missing. >> reporter: montgomery noted a key detail about those pages. >> mary's home phone and cathy's home phone arehe same mber. >> they're the same numbers. >> reporter: so, seeing that number on his pager. how did sam know it wasn't cathy? >> if he knew she was alive, he would know he got 20 or 25 pages from cathy, or at least think that. if he's guilty and he killed cathy, he knows those 20 or 25 pages were not from cathy. >> reporter: that was tell number two. then montgomery noticed how, in his second interview, sam referred to cathy's murder. >> you know? but then happened, and -- shoot. >> he doesn't use the word "murder," doesn't use -- doesn't

say anything like that. it's like, "this happened," as if it's small. it's not that big of a deal, it's not horrendous. he doesn't want it to be horrendous 'cause he did it. >> reporter: tell number three. and then larry caught something else in the interview sam did before cathy's body was found. listen carefully. >> so you went out with her the saturday before the thursday? >> right. >> okay, and where did you? >> in other words a week before she was -- she disappeared. >> reporter: did you hear that? >> a week before she was -- she disappeared. >> reporter: "before she was..." what? dead? murdered? either way, larry thought sam knew more than he was telling. >> the guilty person knows a lot. cannot forget all that he knows. so when he's talking, all that information is in -- is in his brain, and it can slip out. >> reporter: another reason to think sam knew much more than he was saying? in his second interview after cathy's body was found police

spoke with sam for 90 minutes before he asked them a single question. and when he finally did. >> so did you -- do you guys know how she was killed? >> uh, yeah, we do. >> reporter: larry noticed a telling statement. i thought you were never gonna ask. >> well, i didn't want --'cause i don't want memories to come back, you know? >> well, that's an interesting statement, "i don't want memories to come back. what memories does he have that he doesn't want to remember? if he's innocent, he has memories of cathy, good times, what they did. >> people would want those memories to come back. >> yeah. if he had a memory that he killed her, that certainly is a memory he doesn't want to relive. >> reporter: after listening to the interviews time and again the evidence whisperer had no doubt sam killed cathy. but could the team prove it beyond a reasonable doubt? >> ultimately in cold case murders, time becomes of our friends because technology changes. >> reporter: at the time of the murder d-n-a tests could only be

done on big samples like blood spatter. but in the years since analysis became possible for touch-dna the microscopic calling cards many of us leave behind just by putting our hands on something. if sam and xavier 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 'em from cathy. >> so you looked, what, on the ankles and under her arms? >> ankles,rms, i thinknder >> daron wyatt sends out the evidence for touch dna, you optimistic? or are you thinkin', shot in the dark? >> no, i was not optimistic. i was not optimistic. >> because -- 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 gonna quit until i filed this case or i died. or he died, i guess. daron was absolutely dedicated to this. >> reporter: the truth was if murphy declined the case a third time the cathy torrez file would almost certainly go from cold to dead. what would he decide? no one understood the stakes better than cathy's mom. >> daron had told meal that we were going to meet with the d.a. my interpretation of it was that he was going to tell me that -- there was nothing they could do. coming up -- a key piece of evidence arrives. better late than never. >> how long had they known that? >> a couple of months at least. >> and they what, forgot to call? >> is it the smoking gun? when "dateline" continues. you okay? eczema. it's fine.

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>> reporter: it was an early

morning in 2007, 13 years after cathy torrez had breathed her last. >> i was having coffee at a mcdonald's before work and i was reading my bible. it was a little bit after 7:00 when i saw that i had a call from him. >> reporter: from daron wyatt. mary knew he was scheduled to meet with the da. >> my first thought was he was gonna tell me that the meeting was cancelled again. >> reporter: but that was not the message. not at all. >> he said, "i'm standing here in front of sam's house and we are making an arrest right now." >> they're making an arrest. >> yes. >> and you thought? >> and i -- got up and i think i screamed there at the mcdonald's. >> reporter: years before, darowyatt had made a promise. now, he felt, he was keeping it. >> that had toeel pretty goo >> yeah, there were tears of joy this time. >> reporter: sam lopez was arrested and charged with cathy's murder. but he wasn't

alone. just as prosecutors now believed he wasn't alone the night he stabbed cathy to death. sam's cousin xavier was also arrested and charged with murder. police also arrested sam's older brother, armando, who was once married to cathy's sister tina and had helped search for cathy. >> it's just a tragic loss. it hurts. everybody loved cathy. >> reporter: armando was charged with being an accessory after the fact for allegedly helping cover up the murder. >> we believe that he was telling people who had information that could help convict sam not to cooperate with the police. >> reporter: cathy's sister had to ponder what that might mean about her former husband. >> betrayal of the worst kind. >> betrayal of her, betrayal of you. >> exactly, everything. >> your family. >> my family. trust, betrayal, everything's broken beyond belief. >> reporter: sam and his wife had also separated by this

point. she was at work when her sister called her and told her police had once again come for sam. >> what'd you think when you heard sam was arrested? >> the same that i always had. like -- >> not -- not -- "nothin' to it"? >> " --here we go again." it's like -- n -- yep. >> and, "he'll be out soon"? >> yeah. >> reporter: after all, they'd detained sam once before and had to release him. but as daron wyatt now explained to sam lopez, this time was different. >> i've told you before that we wouldn't give up until -- until we were able to bring resolution to this case, and that's where we're at now." >> reporter: but just when it seemed the case was buttoned up, daron got a surprising call. remember the request for touch dna daron had submitted months earlier? the crime lab finally called back. >> and the crime lab says what? >> "hey, did we tell ya that we found xavier's dna on cathy's body?" "what?"

"yeah, we found xavier's profile on her sock, on the back of her knee, and under her right armpit." >> "did we tell you? no, we didn't tell you." how long had they known that? >> a couple of months, at least. >> and they, what, forgot to call? >> i think the examiner who had been doing it was waiting for additional results and didn't realize that she hadn't notified us. >> so the idea touch -- so the -- so the idea of touch dna paid off? >> it did. >> reporter: but not quite the way they had all hoped. >> unbelievable that you would get touch dna evidence back that long after the fact. >> right. >> but bad news, it doesn't have sam lopez's name on it. >> right. that's right. >> reporter: so the strongest physical evidence was still against xavier. but it was sam who had the motive, and he was the first one going on trial, even without a trace of his dna anywhere. it had taken 13 years to arrest sam lopez, it would take another

eight to bring him to trial. and just months before that trial began, matt murphy learned that sam had a new defense attorney. someone matt knew very well. >> he is so good, and would be lyin' if i said my heart was not in my throat. >> reporter: sam's defense attorney lew rosenblum was the former assistant da who supervised the homicide unit. in fact, he was the original prosecutor, who back in 1994 didn't think there was enough evidence to charge sam. not only that, lew was the man who brought matt into the homicide unit. >> lew took me under his wing and trained me how to do homicides. >> what's it like to go up against your mentor? >> well, it's terrifying to go up against your mentor. >> reporter: neither one of them had ever lost a murder case. but someone's winning streak was about to end. february 10th, 2015. 20 years after cathy torrez' murder, sam lopez went on trial.

at the end of this case you are gonna hold that man accoble for exacwh he did. >> reporter: the very first witness matt murphy put on the stand was cathy's mom, mary. it seemed a safe way to start. >> there is a cardinal rule that you don't ever do a hard cross-examination on a mother. >> reporter: but matt's mentor broke that rule. >> he really pressed her on some of the details. >> and scored some points. >> scored big points. i mean, scored big-time points. >> reporter: mary initially told the jury that sam only responded to one of her pages, but under cross-examination mary revealed he'd actually returned three pages. >> they were trying to paint a picture of sam that he did absolutely nothing and that is not true. >> it's one of the only cases i've done in my career where i realized, "he understands this case as well as i do." >> reporter: it was mentor against pupil, and the stakes couldn't be higher.

coming up -- >> it's as cold-blooded as you can possibly get. >> where is the evidence? >> a 20-year search for a killer draws to a close. but as always, the jury gets the last word. when "dateline" continues. itivi. ♪ uncompromising protection... advanced connectivity... and one more thing... the world comes with it. the new, reimagined 2019 jeep cherokee. what does life look like during your period? it's up to you, with tampax pearl. you get ultimate protection on your heaviest days and smooth removal for your lightest. tampax pearl and pearl active. for up-to 100% leak-free work outs.

p3 it's meat, cheese and nuts. i keep my protein interesting. oh yea, me too. i have cheese and uh these herbs. p3 snacks. the more interesting way to get your protein. kyle, we talked about this. there's no monsters. but you said they'd be watching us all the time. no, no. no, honey, we meant that progressive would be protecting us 24/7. we just bundled home and auto and saved money. that's nothing to be afraid of. -but -- -good night, kyle. [ switch clicks, door closes ] ♪ i told you i was just checking the wiring in here, kyle. he's never like this. i think something's going on at school. -[ sighs ] -he's not engaging.

matt murphy was facing the biggest battle of his career against his former mentor, the famed prosecutor turned defense attorney rod rosenbloom. the same man who felt in 1994 there was not evidence to charge lopez. it was an epic showdown in a packed courtroom. >> two of the best attorneys many the nation battling each other over a high-stakes murder with zero evidence on the

defendant on trial. and it was teacher versus student. >> sam had been a suspect for 20 years. and during that time, his attorney said, police had it all wrong. >> could detectives have made up their mind about who did this murder within hours? we had a bad feeling about you, they said. we're going to prove it and they spent the next 21 years over and over trying. >> the defense argued sam's behavior didn't prove anything. not only was sam in touch with kathy's family the week she disappeared, but he also parted in the search putting up a flyer at his girlfriend's store. and that business about him not showing any emotion in the interview with police? >> it is very easy to sit back and say, he should have done that. he should have answered this way. look, he's stretching, he'son g he'syawning, he's reading a coke can. where is the evidence?

>> you would see the man sitting in the chair was not lying to cover-up a murder. >> he voluntarily gives hair, blood, prints, shoes, clothes, everythi they want. not a man who is hiding. that's a man who wants to prove his innocence. >> and the defense said after 14 years of tests, not a single forensic test, not his fingerprints or dna have been tied to kathy's brutal murder. >> everything they expected to find of my client, everything, none of it was there. why? because they're wrong. >> the fingerprint and dna at the crime scene made it obvious. the wrong man was on trial. >> javier lopez is all over this. prints, dna, because he was the one that did it. not my client. >> but prosecutor matt murphy argued that javier's dna and fingerprint were really evidence

against sam. remember, from the beginning, ja javier was sam's alibi. the prosecutor argued if they were together and javier's dna put him at the scene of the crime, then sam had to be there, too. >> his alibi is at the murder scene. and for sam lopez, i think that's just devastating evidence. >> and he told the jury it was the first of many instances where the most powerful evidence of guilt came from sam's own words. >> sam's actions and it's sam's statements. >> he gave you the case against him. >> the best evidence that we have in this case and that we had was sam lopez himself. >> sam was the one who told police he had a jealous streak. >> any time she mentions a guy's name i get missed off, okay? >> cathy was seeing another man

named albert. his jealousy was triggered that night he saw her with another man. >> he gets, in his own words, pissed. >> what he did was slash cathy's tires. >> obviously, someone would have to be pretty angry with her to slash tires. if the tires were slashed, ladies and gentlemen, there's only one person who did it. >> murphy said sam's anger continued to build as cathy's attention turned to albert, the same when when sam asked her to elope. a proposal she told her sister tina she was going to reject on saturday. the day she was killed. >> so now it's not just a hickey, it's a denial of a proposal. and it's all because of another guy. >> the result the prosecutor said was an attack so savage, cathy stabbed more than 70 times, it could only be the work of a jealous lover. >> every one of those cuts meant

something. every one of the stab wounds meant something. >> and the finishing blow. >> she was alive. and sam lopez cut her throat. it's as cold-blooded as you can possible get. >> the 21st anniversary of cathy's murder fell during the middle of trial. a day that reminded cathy's family once again of all they had lost. what did your family do that day? >> we went to the cemetery as we go every year in february. we take the red roses that she wanted for valentine's day that year. >> for 21 year, the torrez family had demanded answers. two days after deliberations began, the jury reached a verdict. >> i couldn't breathe. i felt the tightness inside. and when the clerk took the folder, i started -- my prayer, the lord is my shepherd, i shall

not want. >> we, the jury, find the defendant augustine lopez, guilty of murder in the first-degree. >> once i heard that, all i remember is that i held my hands up to my chin like this and just thanked god. >> baron wyatt was watching mary in that moment. >> this was everything to her. and i wanted to look in her eyes when they came back to see that she knew that i fulfilled my promise. >> for sam's ex-wife, the news was devastating. >> i cried. >> for your daughter? for sam? >> for both. >> doesn't sound like it shook your faith at all in him. >> it didn't. >> after the verdict, people strung little white hearts on the tree that was planted in cathy's memory.

did she leave a mark on the world that she always wanted to leave? >> yes, she did. we have letters of coworkers, of students she worked with. >> people you didn't even know. >> that we didn't even know that were able to come back and tell my mom or tell one of us, you know, we miss her. she was always smiling. she would always help us. so what they did to her, all those stab wounds that she got, multiply those and those are her marks. >> for 21 years, sam denied he inflicted those stab wounds. denied he killed cathy. but at his sentencing, sam did something unsuspected. >> i would like to apologize to the torrez family and to everyone for all of the harm and grief that i have caused them. this was horrible act that never

should have happened. it was entirely my fault. i take full responsibility. >> sam lopez was sentenced to 26 years to life in prison. jaef y javier pleaded guilty to involuntary manslaughter and accessory after the fact and served eight years and is now out of prison. sam's brother armando pleaded guilty to dissuading a witness and was sentenced to one year probation. and mary bennett is still facing the rest of her life without cathy. >> in 1994, i was given a sentence, and there was no parole for me. to live my life without ever seeing cathy again, without ever seeing her beautiful smile or having her come running in through the door and saying, what's for dinner? i will never have any kind of parole from that. that is my life sentence. >> she's serving it one night at

a time because the wee small hours of the morning still call to mary bennett, reading the bible and waiting for dawn while the whole wide world is fast asleep. good morning. i'm dara brown in new york at msnbc world head quarters. 7:00 in the east, 4:00 out west. here's what is happening. secret memo revealed. president trump's legal team argued he has complete power over justice investigations. but does the president really have the power to put an end to the russia probe? and the hard line. no signs of denuclearization, no sanctions relief. >> north korea will receive relief only when it demonstrates a verifiable and inreversible step to denucleariza