treasures, a clue pointing to a most surprising and calculating killer. >> someone with a sick mind. that's all i know. >> here is dennis murphy with "the collector." >> if your travels teaake you to the ozarks, perhaps you have fishing on mind. but there was no tour guide that would have directed you to this modest home in springfield, missouri. that's a shame, because it was an old cureioussity shop well worth seng. valuable stuff everywhere the eye landed. but every object just so. >> everything from coins to arrowheads. he had probably 10 to 15,000 books.

silver, gem. >> bayonets from world war i, lead cannon. >> but did these collectors have a less discerning eye when it came to sizing up people? and that go towards explaining the dreadful toll in the house that evening? >> i said, he's off in some way. i don't know. he could be a psychopath or something. i said, it scares me. >> on april 30th, 2014, did they fall prey to someone they believed could be trusted? >> i had to be lowered to the and i started crying and screaming. >> oh, such good people, why? >> springfield, missouri is called the queen of the ozarks. a church going, neighborly city of mid-size with good colleges. gary tyrell grew up poor on a farm not far away and knew e ely on that his adult life would be all about education. teaching kids in his classrooms

the history book in his lap at night. he and his wife jan raised two kids. a girl and a boyoyho sadly died young of a brain cancer. jan kept the house mainly, and sold i have an sold avon products part-time. they designed their house themselves. life in missouri was good for the two. >> they loved each other very much. >> daughter jessica remembers how extraordinarily close her parents were, joined at the hip. >> if my dad went shopping, my home went with her. they talked on the phone several times a day if they were apart. >> they really were for the ages. >> yes. yes. >> personalities? gary was the fun, outgoing one. >> he was a jolly man, kind of oike a santa claus. >> jan, a little more reserved. >> it might take a little bit more to know her. once she warmed up to you, she was very alive.

beloved assistant school superintendent, he suddenly had all the time in the world to visit civil war battlefields, ovov his antique catalogues. but there was a lucrative sideline to his obsession over memorabilia. gary's brother, larry tyrell. >> he constantly collected coins, bought and sold trinkets.s. >> and did well at it? >> gary was a good businessman. >> the gold and silvlv went into one of the five saves infe ssafes were in the house. >> he had indian jewelry, quality pieces that he loved. >> what was hihifavorite piece? >> probably the walrus tusks. he loved those. >> they were rare, each worth around $10,000.

>> i'm not really sure. they did go to flea markets and garage sales and things like that. any time i would ask him, you kn, where did you get this, he would say, oh, in my travels. >> in 2013, jason murray became one of the family when he and jessica got engaged. he remembers the walrus tusks as well as all the other unusual items in the tyrell home. >> there was so much stuff in that house, yet it was immaculate. it was like an off beat museum. >> jessica a a jason lived almomo 300 miles away in oklahoma city. but jessica spoke with or texted her parents several times a day. but that all changed on may 1st. >> i had called my mom on my way to work, like i always do. and she didn't answer. so i thought, well, maybe she's in the bathroom, maybe she's outside. and i called back and i still did not reach her. >> by noon, jessica says she

police and asked them to go by the house. >> when the officer did that, >> that nothing seemed out of they couldn't see anything inside the house. all the doors were secure. absolutely no signs of forced entry or that anything appeared to be out of place. >> the officer had no cause to force his way into the house, but jessica says she was still worried. car to make the five-hour drive to springfield. they arrived at the house around 7:00 p.m. >> as we were coming around the corner to the house, i hit the garage door button. and both their cars were in the garage. >> that was bad news for you. >> yes. >> what did that imply? >> that there was something terribly wrong. >> jessica called 911 without ever going past the garage into the house. two officers arrived within

>> they entered the me. and then another officer arrived, and then another, and then another, and then another. >> and you're waiting outside. >> i'm waiting outside. >> no one said a word to jessica and jason. they noticed police blocking@off the area with crime scene tape. i kind of grabbed on to the officer and i said, what is going on? why are they calling for crime scene tape? and he kind of, you know, held me and said, i don't know what's going on. all i know is there are two people in the house that are deceased. >> chilling words outside the tyrells' house. but t ey were nothing compmped to what investigators would find inside. when we come back -- >> it seems to be an element of personal anger. >> it definitely seemed to be

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>> reporter: as darkness closed in on springfield, missouri, the police to check on her parents, was now being told two bodies

home. they didn't identify them but jessica says she knew it could only be her mom and dad. >> and i started cryink, and screaming. because i knew it was -- it was my worst fear. >> reporter: her fiance, jason, was by her side, trying to console her. >> she was -- beyond upset. mom. i'm sorry, mom." >> i had no details -- had no idea what had happened. >> i'm thinking, "this is horrible." and also, hoping it's like carbon monoxide, something along -- >> something. but not benign, but something explainable? >> right, right. >> reporter: but inside, officers qckly grasped the cold, stomach-churning truth. jan and gary's deaths were not accidental. >> it was gonna be a long investigation. >> reporter: detective neal mcamis was one the first deteteives on the scene.

through the garage door and saw gary first. >> we could see that there was a deceased male in the hallway of the home. >> h h pants were pulled d dn. what did you make of that? >> we didn't know. the only thing that -- we could think of was he's trying to get away from somebody, that they're grabbing a hold of him. >> reporter: or wawathe killer rifling his pockets for something? a key, maybe? a combination? in gary's office downstairs, the detective saw jan. >> she was on the ground. she was lying fafa down. but it was -- it was obvious that there was severe trauma to the back of her head. >> reporter: so was this a olent home invasion? jan and gary had more than a half a million dollars worth of valuables in the house for the grabbing, so a botched robbery was a likely scenario. and in the garage, police did find strange marks and scratches on a tornado shelter that was also used d a safe. >> it appeared that somebody had -- tried to pry the lock open. there were some marks that -- that were by the -- the lock on

shelter. >> they didn't get i.side. >> and it did not appear that they did, no. >> but that would suggest somebody's looking for something. >> yes. >> reporter: but if robbery was the plan, the killer had left the oddball museum strangely intact. nothing appeared tossed or out of place. and the nature of the killings -- gary was shot as well as beaten, spoke volumes to the prosecutor assigned to the case, todd meyers. >> it seems to be an element of personal anger in this thing, todd. this close quarter killing of somebody with -- with a weapon in your hand. >> yes, it definitely seemed to be a personal-type killi, just the brutalaly involved. >> reporter: investigators determined jan and gary were likely killed the night before. but search as they might for the murder weapons, the gun and the bludgeoning instrument. officers came up empty handed. bubuthey did recover some unusual evidence.

small white flakes of a substance that were obviously either from the murder weapon or on the murderer's body. there were similar flakes found by the wound to gary's head. >> reporter: so they bagged them and sent them off for testing. and the crime-e-ene techs recovereresomething else that could be a crucial piece of evidence -- a discarded latex glove. >> so a latex glove on the floor jumped out at you. >> totally outta place. and from t tking with everybody, that there is no way that gary or jan would have left that glove there. it was right in the middle of the floor for everybody to see. >> reporter: did it belong to the victims or the killer? no one knew. >> so it's collected. you don't know what it means. >> we don't know what it means. and it was collected. sent to the highway patrol crime lab. >> reporter: they had no idea. bo working theory yet of why the couple had been murdered. but they did have a sequence that made sense as to the order of deaths. >> it is hard to believe that gary is shot upstairs if jan is still -- fully functioning andnd

called 911, would not have tried to intervene in some way. >> speculation, but common sense tells you, she's the first victim. >> she's the first victim. yes. >> she's bludgeoned to death downstairs. gary arrives at some point later. >> and most likely he arrives -- either while that is ongoing, or the killer is waiting for him. but yes, it appears that she would have beeeethe first to have died. >> reporter: a big question early on for detectives was understanding their crime scene. how did the killer gain entry to the house? >> there were no signs of forced entry. >> windows haven't been forced. the doors are all intact. how did the killer get in? >> there are only two ways the killer could have gotten in. one would be to have -- their own access device, whether it's a key, a garage doorpener, some way that would open the doors up. and then upon leaving, be able to lock it that way. or, to have been let into the house by either gary or jan. >> reporter: it didn't appear to the cops to be a random home invasisi -- but rather that the killer or killers had been

was it a person gary encountered in his antiquing travels? or -- terrible to think about it -- was the perpetrator someone much closer to home. was this all in the family? >> i was shocked -- really confused, and bafflele be. coming up -- who had a motivate to kill the tyrells? investigators have at least one idea. >> she is the person who could benefit from this crime in terms of getting money. >> she's the only child of parents well to do with a lot that's going to be left to her. >> when "dateline" continues.. life is unpredictable, so embrace it!

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>> reporter: two dead. the wife beaten about the head downstairs. the husband shot twice upstairs. and spririfield police had determined this was no random break-in gone wrong. jan and gary tyrrell's modest home was filled with valuable items. and yet, at first glance, nothing appeared to have been tatan. an early supposition was their killer was likely someone close to them. and no one was closer than daughter jessica. >> she is the person who could benefit here from this crime in terms of getting money. >he had the most to gain. she's the only child and -- who had -- from parents that are very well to do with a lot that's gonna be left to her. >> so, she's gonna be questioned hard. >> yes. >> reporter: so that night, detectives asked jessica and fiancee jason down to the station to answer a few questions.

talking to them not just as grieving relatives. but also as potential suspects. >> i'm obviously going to take a few notes, obviously, as we're talking. so don't let that, uh, don't let that bother you. >> reporter: the interviewer withheld detaiai about the crime scene. a standard investigative tactic to see if a subject knows more than they should. he even threw out a theory that wasn't true - murder suicide. >> one of the things we have to look at is as to whether or not that one of them would've injured the other and then maybe themselves. >> reporter: jessica seemed to go with it. >> do you think that's a possibility? >> my dad, since his mom died, has been super depressed andndas made comments. and my mom called the doctor's office, and i told her if he did -- if he said something stupid before, again, that she needed to call the police. like get the [ bleep ] away from him and call the police. >> reporter: and as they continued talking, police had another reason to be suspicious of&the daughter. she'd driven 5 hours to check on

then didn't go inside the house. >> and you wonder why she would do that? >> yes. people sometimes that commit a crime or know a crime that's been committed, you know, they don't wanna see -- the bodies in there so they call somebody else. >> reporter: detectives pressed the couple about their movements that day -- what they did or did not do at the scene. had they tampered with that tornado shelter in the garage. >> you guys didn't do anytytng to try to get inside? >> oh no, no, no, no, no, no. i mean i pushed my hand on the handle, it was locked and that was it. >> did you think, "are we looking at maybe -- having a situation here where we gotta call a lawyer or be careful about what we say?" >> reporter: but neither jason nor jessica asked for a lawyer and offered the detective more tornado shelter that had been tampered with. gold, and silver, and gold bars and i don't even know -- >> we actually don't know what all's in there. >> i don't, i don't -- i mean he has books that are signed by presidents. he has indian peace medals. >> reporter: f f investigators, the entire interview was a test.....

are you gonna give answers that we can go back and verify? are you going to respond appropriately-- >> so you intend to sweat them? >> yeah, that was the detective's intent -- to the degree of just trying to make sure we get the truth. >> reporter: so had they passed the investigators test? detectives let them go but held onto jessica's car to test it for potential evidence. >> why did they have a reason to look in your car? >> i didn't really know. i assumed it was just because my car was there. >> reporter: now jessica had to call family and friends to tell them the news about her parents. her uncle larry, her father's brother, was at his law office when he got the call. >> she said that--om and dad are gone. i said, "what do you mean? are they out of town?" ananshe said, "no, they'y'-- they're deceased." well, i collapsed on the floor. >> you were a mess. >> i was a mess. the unknown was terrifying -- because i didn't know what had happened. >> reporter: but larry wasn't

potential suspect. he was, after all, a criminal defense atatrney and former prososutor. eliminated. i understood that-- due to the fact that she was the only child. i mean -- she just had to be eliminated so that the case could move on. >> reporter: and the case did keep moving--- but after a full week of investigating, the daughter and her fiance were not eliminated. rather, detectives c cled them back to the station, this time interviewed separately. jason first. cops by now had figured out that the murders ok place the night before the bodies were discovered---so where exactly were he and jessica then? >> we went to the pizza hut on -- i don't know, probably 5:30 or something like that, then came back home, and stayed home. >> reporter: home, five hours away -- in oklahoma city. >> do you remember how you paid for the pizza hut stuff? >> i'm sure it's on my card. >> credit card. >> i'm sure it's on my card. >> reporter: then, right to the point.

harm gary or jan? >> not at all. >> didn't do anything to hurt them? >> no sir. >> didn't go into the house? anything like that? everything you're telling me is the truth? >> absolutely. >> reporter: next jessica was in the chair, answering questions about her relationship with her parents. >> were they paying any of your bills, cars? >> they -- they pay my at&t bill for my cell phone. they pay my car r surance. and i think that's it. >> i'm just gonna ask. did you have any ill feelings toward your folks? anything that you would have been mad -- mad at them for? any reason to want to harm them or anything like that -- >> no. my parents were my life. >> to better, better your financial situation or anything like that? >> no. i mean, if i needed something, all i had to do was call and ask. >> so you're a suspect-- >> right. >> --in your parents' double homicide? >> yes. yes. >> how do you deal with that? you haven't even buried them yet. >> i wasn't really dealing with it.

and saying -- i, you know, i didn't do it. >> reporter: police asked both jessica and jason for dna samples, then set out to verify ththr alibis. >> my boss and i took a trip to oklahoma city and we went to employers. spoke with-- fellow employees. with jessica's boss. and we went to the pizza hut to see if we could see some-- surveillance video. >> reporter: would it all check out? or would an unexpected lead send the investigation in a new direction? >> this was a huge bingo moment. >> it was. coming up -- gary's best friend offers detectives some clues, including texts he says he saw on gary's phone. >> some guy that was asking for money.

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>> reporter: on an early spring day jessica tyrrell had planned to go wedding dress shopping with her mother.

she was instead, burying both her r rents. >> i basically just cried, and -- was constantly ill. >> what she was going through at that point is just unfathomable. i mean, she is just broken at this point. >> reporter: the funeral service was s ld at a high school in the mountain grove school district where gary worked for 30 years. nancy littrell was a school board secretary. >> j jt so hard to believevehat something so bad could happen in springfield and double unbelief that it's somebody you know. my heart has just gone out for poor jessica. >> reporter: the outpouring of love and support was a huge comfort to jessica at a time when she needed it most. word had gotten out that cops were looking at her. >> yeah, lots of rumors that i did it. >> that's tough to go out every day and say, "i didn't kill my parents." >> right.

tiring to hear, you know, someone say, "well, you need to look at the daughter. she did it. she has the most to gain." >> and they did take a hard look. >> yes, they did. >> they think the daughter has killed him in order to get the money, that she's in cahoots with her fiancee.. >> isn't that awful? >> you might not have believed it, or your circle of people didn't believe it or knew -- >> my circle -- my circle was not believing that. >> reporter: and behind the scenes, police and prosecutors had come to the same conclusion -- jessica and jason were innocent. >> everything that jessica and jason were telling the police, the police were able to corroborate and verify. >> and they went through everything. they went through the phone records. the alibi was checked out top to bottom. >> it was. >> reporter: and when the dna results came back on the latex glove, neither of them was a match. it belonged to an unknown male. >> w that a relief for you? >> yes, i mean, we knew we didn't do it, so, i mean, it was, like, "okay, well, now you need to find who did it." >> reporter: and the couple felt they could help the investigation with their own amateur sleuthing. for instance, when jason went back to jessica's parents' house

something was missing. >> there was a display of little ivory pieces and multiple walrus tusks thth, you know, kind of engraved art type things. and they had been moved. >> walrus tusk, jason. are we talking about like -- like so? >> the big one was about yay big. right. the larger one was not where it was supposed to be, and the other one was not there at all. >> reporter: jason told police that one of gary's prized tusks could be the murder weapon, the source of those mysterious white flakes. and jessica noticed something, too. someone had been at her dad's desk where he sorted coins. >> he kept them around his desk in coffee cans, and -- bags -- you know, that -- and he would organizing them. >> reporter: and a container with what would have looked like loose parking meter change was missing -- it's actual value -- around $20,000, according to her dad's records. the killer would have known the real value only if he moved in

gary. at least that's what the brother suspected. >> perhaps someone he -- gary had went to buy some gold or silver and that someone had set him up and that had someone follow him home and got the drop on him or jan and -- had robbed him and killed him. >> it sounds very plausible. >>8that was a big worry i had.% >> reporter: but as they dug into gary's business dealings, no potential suspects emerged. few people had any idea how wealthy they really were. >> they d not show that type of wealth to people. it was always kept very quiet. the people that he wouou interact with, as far as selling the gold were always very reputable-type people. >> reporter: and because there was no forced entry to the home, larry offered up the very limited list of people who had access to the house, a handful of local contractors. >> i assume you were -- asking the garden guy, and the cabinet maker, whoever might have been in thax house from larry's list of people to give dna. >> right. >> reporter: at the same time, officers were reaching out to others in the couple's inner circle. gary's closest friend was

two, prominent guy in town and former school superintendent. >> it's just a wise thing to do to clean the floors. >> he was handsome. he lookegood. he dressed good. when he first came to the didirict, he drove a jaguar. >> reporter: nancy worked with both gary and mark. >> they seemed to get along really well, worked well together. i thought they were friends at school and off of school. >> reporter: so mark went down to the police station to talk with investigators. >> all right mr. porter. is it -- it's mark? correct? >> yeah. >> do you mind if i call you mark? >> no, that's good. >> okay. >> i just want to kind of touch base with you and talk to you a little bit about how you, how you know them, how long you've known them. >> well, gary, since probably maybe 15, 20 years. he was my assistant superintendent. i was -- i was the superintendent. >> reporter: mark knew a lot about gary's coin business. he'd started dabbling in it as well. he told detectives details that suggested a fellow collector could have targeted e tyrrells.

the -- missouri that collect for him, and i know he goes to hotels, and meets people and he's -- he runs ads in the paper. >> repepter: according to mark, gary set up one of those meetings around the time of his death, and it involved a lot of money. >> he was actually going to sell $50,000 of gold for cash. it was -- it was actually a buyeyewho was going to givivhim $50,0,0 cash. that's all i know. >> reporter: he also mentioned text messages he'd seen on gary's phone from some other guy. >> gary asked me to read him some of his text messages and therwere five in a row from some guy that he had taught in a class that was asking for money. >> okay. >> and i have no idea -- >> you don't remember? was there a name attached with the text? was it just from a number? >> i can't remember. >> reporter: and remember, gary was shot as well as beaten. could it have been with one of his own guns? >> gary has guns everywhere. gary has guns in -- in every drawer of the house i think. i mean, he likes his guns. he loves guns. >> reporter: but then, mark gave detectives a detail that took

>> he was supposed to meet me actually 8:00 on, uh wednesday, and didn't show. >> reporter: wednesday, the night of the murders. it was the first police were hearing of gary having plans that night. what else did the best friend know? coming up, mark gives a detailed account, one that troubles investigators. >> there were several things about that story that raised questions. >> then larry's brother reveals who he thinks had a motive for murder. >> i know he had some sort of bad financial ise.

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>> reporter: springfield police were talking to gary's best friend, mark porter, whoho suggested plenty of theories about why gary was killed. he said gary's money was catnip for all kinds of folks. >> you know people who knew him, if they knew he had money were always asking. >> reporter: then mark revealed something detectives didn't know. he and gary had plans to meet at mcdonalds on the night of the murders. >> and how long do you think you waited on him? >> i waited probably a good, i got there probably 7:45. uhm. probably 45 minutes. detective: okay. >> reporter: so the friend said he drove across town to stop by

>> i went back to the house, knocked on the door, nothing, didn't answer so i thought he had either gone or he had left, cause sometimes, cause he'll leave. he'll go and say, "oh man i forgot, my uhm my bad, i'm, i'm in kansas city," so i had no clue. >> reporter: mark told detectives that gary had stood him up before. no big deal. so he went back to his office at ibm to do some work. >> now, there were several things about that story that raised some questions. >> like? >> like, why would you wait 45 minutes for someone and not pick up your phone and give 'em a call, and say, "hey--". >> what's up? >> what's up? did you forget?" >> reporter: but what seemeded really strange was that mark porter had just admitted to going to the house the night of the murders, with a story that just didn't ring true. why drive across town if he wasnsn all that concerned d out his friend missing dinner? >> so he drives a few miles across town to go knock on the door, when his office is across the street, when it doesn't appepe that gary is showininup. >> so he puts himself at the house?

explanation, huh? >> yes. >> reporter: inside the interview room, the detective decided it was time for a break. >> ge me just a couple seconds i'll go back there and see if there's anything else. can i get you anything? coke, water? anything? >> no. >> reporter: trying to make sense of it all, including this bit of information. gary's brother had told police that not long ago mark asked gary for a loan put the request in writing and not just a little bit til payday but an eye-popping $250,000 dollars. >> that's the e nda money if you can get it out of your house as a second mortgage maybe you're-- you're lucky. >> right. right. >> what did your father make of it? did he consider it even for a heartbeat? >> no. not at all. when he was talking to us about it-- he was kinda laughing and said, "you know, i-- i don't know where he thinks i would have this kind of money." >> reporter: strange, since not only would mark, gary's former boss, have had a nice pension as a former school superintendant, he was currently earning a six figure salary at ibm.

might have a gambling problem. >> i knew he had some sorta bad financial issue. >> reporter: when the detective came back to the room, the tone of the interview had changed completely. >> have you ever had to ask gary for money yourself? >> uh onon, no. only for uh only uh in trade or buying. >> reporter: suddenly, mark porter was in the hot seat. information from somebody who told me that maybe you had a large gambling debt that you were ask for -- >> i do not have a large gambling debt. >> gary for. >> no. >> for maybe some assistance >> no. >> that's false? >> yeah, that's not true. >> reporter: he denied asking for the loan said the only time he discussed large sums of money with gary was about a real estate deal. >> because he, he's always looking r investment, whatever. >> r rorter: then detectives asked d m the question they'd asked everyone else would he offer up a dna sample? >> all i have is just like a cheek swab that i would ask if you're fine to do that while you're here today. >> no i'm gonna wait. >> okay.

ow the legalities. i ion't want to, i don't want to do something and my attorneys say i shouldn't have done that. >> okay. >> why would you not give us a dna sample? >> he's your best friend. we're trying to find his killer. >> he's your best friend. we're doin' everything we can to try to find who brutally murdered your best friend. and you're tellin' us that you're not sure you're gonna give us a dna sample. >> reporter: the refusal wasn't evidence of mark's guilt so police let him go. but the investigation suddenly shifted away from the workers at the tyrrell home and toward mark porter. some detectives hit the pavement to check out his alibi while others continued mining other avenues for leads. one cop thought to check a local database of pawn shops to see if any of the missing items from the tyrrell house had been recently sold. that search led them here to r&k coins. >> tell us how your business ended up bein' very important in a murder investigation in springfield. >> yes, sir. >> reporter: it was just two days after jan and gary were killed w wn kelly eddington was

guy with a tub of coins walked in. >> what were you seein' in him? was he okay? was he normal-- demeanor-- >> he just looked like any average guy to me. i didn't, nothin' actually stood out about him at all. >> he had piles of dimes, quarters, 50 cent pieces. when you added up the face vavae of that stack of money, ho wh-- what was it worth? >> he had $1,200 and $1,210 in face money. >> but the meltdown value of the metal itself was worth what? >> i paid him $18,351. >> reporter: $18,351. a lot of money and not far off the value of the coins jessica reportedissing from her parents' home. >> when he walked ininnd stacked his coins and you did the transaction, your security cameras caught it all, huh? >> sure did. >> so who was it? coming up, how an mcdonald's coffee cup was about to blow the

does your dashboard just light up when you hear that? >> i can't en describe the emotion of it. >> and finally, a family learns the truth. >> i remember falling to the floor.pill stop. can i get my aleve back yet? for my pain... i want my aleve. get all day minor arthritis pain relief

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detectives finally had a major break in the investigation. silver coins worth around the same amount as t t ones taken from the tyrell home had turned up in a local coin shop. surveillance cameras caught the transaction on video. the man certainly looked familiar. but if there was any doubt, he left a copy of his i.d. >> mark porter. mark edward porter. th's a real license. >> that's him. >> but selling a load of coins didn't prove mark porter was guilty of murder. remember, mark also had an interest in the coin business. >> his explalation was these were coins he had, it was just a coincidence he happened to sell them the day after the tyrells

>> by all appearances a pillar of the community was now a prime suspect in the murders of jan and gary tyrell. >> i never did like the guy. i didn't trust him. i thought he was something of a fake. >> gary's brother larry always had a bad feeling about mark. and he was convinced if mark was the killer, the motive was money. >> i felt he was befriending and grooming my brother so he could gain access to his money. i think over a period of time he saw jan as an obstacle. >> when jessica learned detectives were looking at mark, she wasn't surprised. >> she didn't show up at the funeral. >> conspicuous by his absence? >> it was pretty obvious at that point that there was something going on. >> his former secretary said she hated working for mark porter. ended up quitting her job to get away from him. >> he's off in some wawa he could be a psychopath or

>> you used that word? >> i did. >> but what bothered police was his lack of cooperation. >> he wouldn't give dna. he wouldn't take a polygraph. >> add to that the suspicious pawn shop transaction, and the story about stopping by the tyrell house the night of the murders. >> she had talked about making a couple of phone calls to mark and she couldn't get ahold of him, didn't know where she was or what he was doing. >> but police still needed physical evidence. a dna sample to match tohe lay latex glove fofod at the scene. >> we had undercover officers that were constantly doing surveillance for weeks and weeks and weeks to try to somehow obtain a d d sample from him. >> but nabbing a sample approved to be more difficult than expected.

continued to come up empty. >> they watched him eat his lunch. they watched him get a to-go cup. they were all excited because they thought they would be able to get the straw he used oy to see him leave with the straw. so he knew that you guys had eyes on him? >> it's difficult to know what he knew at that time. >> then three months after the murders, an undercover officer followed mark into an automobile oil chain shop. >> egginghe goes inside. mark has a coffee cup he had gotten from mcdonald's. he drinks from the coffee cup. he strikes up a casual conversation. >> the suspect and the undercover cop. >> the suspect and the undercover cop. he leaves behind the coffee cup. >> police had their sample. in less than 24 hours, they had

>> it's confirmed, it's a match. the same dna from m e coffee cup and the same at from the latex glove. >> does your dashboard light up because of that? >> i can't describe without emotion that we'll be able to tell the family that we have some news. >> how do you take that? did he say you've got the wrong guy? >> absolutely not. he said, okay. that's all he said. >> jessica was at work. >> two of my very good friends were with me. he said, he's been arrested. i remember falling to the floor and just being so overwhelmed with relief that he was finally caught. >> even the former secretary who dn't like him was horrified. >> i couldn't believe it. i mean, oh, i thought, no. no.

mark's wife e d told her that her own husband's story put him at the scene of the crime. >> you really need to help us out here. >> when does mark say he was there? >> at the time they were killed. >> no. >> yes, ma'am. yes, ma'am. >> still circumstantial. >> and that's exactly what mark porter's defense attorney argued. mark hired one of the best to plead his case. >> a spotless record, five college degrees, has an outstanding past of good reputation. >> at a bond hearing, the defense revealed its strategy. they would argue there was nothing suspicious about mark's dna inside hisest friend's house. he was a regular visitor tthe house, he would get with gary, they would put on their gloves and handle the old coins and objects and that's why the glove was there. jurors, it's benign. is that how it works in the real

>> potentially, yes. >> what about the suspicious coin sale? there was no way to know they had come from gary's house. and as to mark porter being a come compulsive gambler? did he owe money to people? >> there was never any evidence we found that led to that. >> so the case, a potential death penalty one, was not airtight. when mark hired new attorneys who asked to t tk about a plea deal, the prosecution was willing to listen. >> what are we willing to risk? to try to get the death penalty, can we achieve what we need to achieve without the riskskf going to trial? >> he could walk. >> there's a chance of a hung jury and you have to do it all again. or they coulcome back on a lesser crime. >> both h des agreed. mark porter pleaded guilty to

sentenced to prjson. no eligibility of parole until age 82. >> i'm shocked and sad. i have a lot of relief that mr. porter is finally going to be behind bars for presumably the rest of his life. he has to live every day with what he did. every day he has to think about what he did. and all of the lives he destroyed. >> you're ying you have to live with remorse, but you haven't seen any sign of rererse. >> that is the only bad part. but he still has to sit there. >> today, jessica is doing her best to move on. in february of 2015, she and jason finally got married. >> we got married on valentine's day. it was a great day. it was also very sad. my parents weren't therere >> larry took his brother's place and walked her down the aisle. >> she asked me to give her away. it should have been my brother's job.

>> mm-hmm. that's true. i was honored to do it but i didn't feel right doing it. >> to keep her parents' memory alive, jessica has set up a scholarship in their names. as for thehe offbeat museum of a a home, it's still there, with a loving daughter as caretaker. >> i still feel them there. they loved that house. my mom built that house. i grew up there. and so i can't let that go. that's all for this edition of "dateline." we'll see you again friday for an all-new two-hour "dateline" at a special time, 9:00, 8:00 central. and of course i'll see you each week night for "nbc nightly news." for all of us at nbc news, good night. to get me into that jock feel.

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