it sometimes takes a special eye to look at a crime scene and spot the one thing that's out of place, the clue that will crack the case. in this story, that thing appeared so inconsequential, no one even knew what it was let alone what it meant. it took almost two decades, a team of determined investigators, and a detective with an unusual background to find out. here's keith morrison with "the night before halloween." it was the night before halloween, october 30th, late, midnight approaching. it happened in one of the middle-class suburbs that sprawl across the los angeles basin inside a fast food franchise closed for the night. a frantic scrambling, running feet, then silence. the next morning, not far away, the hoynes family daughters prepared for a favorite celebration. kim was the eldest, then robin, tricia and wendy. excited because this was halloween, one of the best days of the year. >> i loved it. we would trick-or-treat and then sort the candy and we would be trading what we liked. >> a halloween morning long ago, it was 1984, the morning after the incident in the fast food place. it started warm and sunny, that bubble of innocence, before anyone knew a thing. wendy donned her halloween costume, wore it to school, as did tricia who wore hers to work. kim, the eldest, left early for her job at the nearby mall. robin wasn't home. after working late, she told her family, she had arranged a sleepover at a girlfriend's place. she was due home any minute, as wendy remembers. >> she was good about reporting in, telling us where she was going to be and when she was going to be home. >> robin was 21 years old. she was a redhead, pretty, popular, friendly. she was an assistant manager at a kentucky fried chicken franchise in the nearby town of torrance, had taken that late shift as a favor to a co-worker named cheryl. >> i had asked robin if she would trade hours with me. i had just started dating somebody, and we had plans. >> so robin worked the late shift. she had closed the restaurant, count the cash, carried it across the parking lot to the bank deposit box. >> i knew robin was very cautious about, like when i went to the store, she would always tell me make sure the door is locked. >> this is not the sort of person who would have let someone in just anyone? >> no, not at all. >> so when cheryl arrived at work and pulled into the kfc parking lot -- >> i saw be robin's car. i thought, did she get mixed up or did she think i wasn't trading? why is she here? >> cheryl crept through the empty kfc, everything seemed in order. until she entered the kitchen. >> and as i came around the corner, i looked, and i thought, why did robin spend the night here? that was my first reaction. and then when i looked closer, i saw that she didn't spend the night, that she had been killed. >> she ran out of the place. someone called 911. detective jeff lancaster was among the first to arrive at the crime scene. >> she was laying facedown. she had a pool of blood under one side. she had some slash marks to the left side of her face. neck injury from a slashing type wound from a knife. >> it didn't take lancaster long to figure out what happened. this was no accident. >> she had two knife wounds to her back, the right side lower area near the spine. >> it looked, frankly, elementary. robin had been murdered in what appeared to be an attempted robbery. >> the top cover of the safe was removed, and there were some paint chips missing off a new combination lock. >> there were a few drops of blood on the safe, but no fingerprint, no murder weapon, but there was something rather odd lying near robin's body. >> it was just a piece of foam rubber. we kind of speculate that had it came from some padding maybe for a backpack or a handle for a briefcase. >> whatever it was and wherever it came from, the mysterious piece of foam wasn't much to go on. still, they bagged it, put it with all the other evidence. robin's wallet told them who she was, where she lived. an officer went to the house to notify the family. no one home. he left a note which said call the police department. it was something about be robin. >> so i called back. i said, is she all right? and he said, no, she's not. >> so, now kim, the eldest of the four daughters, had to reveal the news. she started with their mother. >> the first words out of her mouth are, you're lying to me. you're lying to me. she couldn't, you know, she couldn't believe that. so once she realizes really that i'm telling her the truth, we know we have to talk to my dad. we called him and told him, and he said, okay, i'll meet you at the house. >> wendy, the youngest, heard at school that robin had been stabbed. >> my immediate response was, did she die, because i want her to still be alive, but she said, no, she's dead. >> tricia didn't hear a thing until she got home from work. >> i had dressed up for halloween as well, and i was wearing robin's flagster costume and i see that i'm in her clothes, and i lost it. i was like, get it off me. i was screaming that i needed to be out of -- i just freaked out. >> time doesn't wait, of course. darkness fell, halloween, laughing kids came to the door. the hoynes sat in the dark and tried to get used to the idea of what grief feels like. policemen buzzed around the kfc all day halloween day looking for something to go on. but all they came up with really was what didn't happen. >> there was no signs of forced entry. she had let somebody into the business, so we felt she knew somebody, and she felt comfortable enough to be working on her paperwork while that person was in the business. >> but who killed robin hoynes? a former friend? a customer? a colleague from work? could it be that robin hoynes had been murdered by someone she knew? as police search for clues that would lead them to her killer, robin's co-worker, cheryl, remembers something. coming up -- >> he was going to come back and return his uniform. >> who was he and did he know anything about what happened to robin? when "dateline" continues. oh, man that is wrinkly. like, not even just a little wrinkly, that's a whole lot of wrinkly. there are wrinkles on top of wrinkles! how do you even let your clothes get that wrinkled? how?! at least my shoes look good! looking good starts with bounce wrinkleguard. the megasheet designed to help prevent wrinkles in the dryer. introducing new vicks super c and dayquil severe convenience pack . [coughs] dayquil severe for you... and daily vicks super c for me. vicks super c is a daily supplement to help energize and replenish your body with vitamin c and b vitamins. dayquil severe is a max strength medicine for cold and flu relief. it's the daytime, coughing, aching, stuffy head, fever, power through your day, medicine. someone is feeling better. get your shoes. alright! try the new vicks convenience pack. it's another day. and anything could happen. it could be the day you welcome 1,200 guests and all their devices. or it could be the day there's a cyberthreat. only comcast business' secure network solutions give you the power of sd-wan and advanced security integrated on our activecore platform so you can control your network from anywhere, anytime. it's network management redefined. every day in business is a big day. we'll keep you ready for what's next. comcast business powering possibilities. the 1980s were violent years in l.a. -- drug wars, gang shootings. the dismal average was nearly four killings a day. but this was different. the murder of the kfc halloween 1984. this was certainly not a crime-infested neighborhood, and robin hoynes was a careful, safety conscious, churchgoing young woman, not an enemy in the world. but she was stabbed in the back by someone she might have known. it didn't make sense. >> the kindest hearted person you probably would ever meet. >> yeah. >> so now the four sisters were three. >> i just was completely lost. at 16 you don't have the capacity to really understand grief let alone to understand grief that comes from your best friend, the person that you -- you know, she sleeps in the bed next to you every night. >> and that bed is empty now. >> is not there anymore because she was murdered. >> the hardest thing then and now was to imagine who would do such a thing and why. >> someone deliberately took her life. this was a heinous crime. >> in the days after the murder, the police cast around for clues, motives, suspects, and there wasn't much to go on, beyond that one puzzling piece of foam they found on the floor near be robin's body. though none of the detectives could even figure out what it was let alone what use it could be as a clue. but as they looked hard at the crime scene, tried to piece together what must have happened, they began a troubling motive that might lead to a suspect t. appeared this was not the work of a random stranger. >> there was no indication of forced entry. there was no indication of a struggle. >> that seemed pretty clear from the autopsy. robin had been stabbed to death, attacked with a knife. but there wasn't a mark on either of her hands. no defensive wounds. that suggested she never saw it coming. when she answered the door, must have been, what, she had money out on the counter and saw someone coming and put it in the safe? >> that's the information i received from a manager. the money was on the counter and she was doing her night paperwork. she had enough time if somebody knocked on the door to identify them, maybe not trust who they were, and put the money in the safe and then allow them to come in. >> there was one way to start confirming that. cheryl, the young woman who had switched shifts with robin, knew the safe's combination. >> when i opened the safe, the money was still in there. i thought it was weird that it was in there because we normally would take it to the bank at night. $600, along with all the night's receipts, were neatly stacked inside untouched and left behind by the killer. there were those scratch marks as if someone tried to pry the safe open. was it possible the killer intended to open the safe after disposing of robin? and if that was the plan, then something obviously went haywire. did it seem to you as if he had gone there to rob the place, that he knew that she knew him, so he had to kill her before he robbed the place? >> yes. >> but then he got nothing anyway. >> and he got nothing out of it. not one thing. such a cold-blooded situation. >> but who would robin have let in late at night? it was after hours. the kfc was closed. she was all alone. >> i knew william was supposed to come back that night. >> william? who was william? >> he used to work there. earlier that day william called me. he was going to come back and pick up his briefcase and return his uniform. and so before i left that day i just told her, william is going to be by later. she said, okay, no problem. >> william was william marshall, a former kfc assistant manager who worked alongside robin for several months. he was young, just 23, ambitious, known to be friendly, quite religious, just like robin. did he know anything about her murder? well, it turns out he did. but it would take detectives some 23 years to find out just what, what he knew that night before halloween. coming up -- the case finally feels like it's heating up, and then it stopped cold. >> i felt like i had been kicked. >> when "dateline" continues. two loads of snot covered laundry. only one will be sanitized. wait, what? adding lysol laundry sanitizer kills 99.9% of bacteria detergent alone, can't. maureen is saving big, holiday shopping at amazon. so now, she's free to become ... maureen the merrier. food is her love language. and she really loves her grandson. like, really loves. ♪ and i'm gonna keep on lovin' you, ♪ ♪ 'cause it's the only thing i wanna do. ♪ turns out everyone does sound better in the shower. and it turns out the general is a quality insurance company that's been saving people money for nearly 60 years. ♪ 'cause it's the only thing i wanna do ♪ shaq: (singing in background) can't unhear that. for a great low rate, and nearly 60 years of quality coverage - make the right call and go with the general. maureen is saving big, holiday shopping at amazon. so now, she's free to become ... maureen the merrier. food is her love language. and she really loves her grandson. like, really loves. facing expensive vitamin c creams with dull results? olay brightens it up with new olay vitamin c.on. gives you two times brighter skin. hydrates better than the $400 cream. we see you. that's why we designed our new no7 pure retinol range. informed by 15 years of scientific research; to target the appearance of dark spots, wrinkles and boost radiance. and formulated to be gentler to skin. it was a start, the first lead in the robin hoynes murder investigation, a name had surfaced, william marshall. marshall was a former kfc employee who had worked with robin at the very same restaurant where she was killed. on the night of the murder, he was supposed to stop by the store. >> he was due to return some equipment or a uniform and also pick up a briefcase that belonged to him. >> a kfc uniform, which william marshall didn't need anymore, and for a very good reason. >> william marshall had been terminated because of missing cash and failed polygraphs. they had two situations reported to the torrance police department concerning thefts of cash from the safe. >> two thefts from the very same safe robin had left the money, and though they couldn't exactly prove he did it, marshall was a suspect. he had the opportunity. he failed the polygraph when questioned about those previous robberies. and at the time, he knew the combination to the safe. so the night robin was killed, did marshall intend to rob that safe again? >> he knew the previous combinations. i don't believe he was aware they had changed it because it had happened just recently, several days earlier. >> so now detectives brought marshall in for questioning, and he was friendly, cooperative, said he was home the entire evening. and he could prove it, he said. all police had to do was go ask his girlfriend, yvonne hargrove, without telling her why they were talking to her, they did ask. >> i told them william was with me that night, because that's what they wanted to know, and what did we do. i said we cooked spaghetti dinner. >> yvonne seemed credible, never wavered in supporting marshall's story. it was a solid alibi. maybe the marshall idea was a dead end. as they were leaving the cops had one more question, though, did she know anything about that mysterious piece of foam found at the crime scene? >> and they brought out this thing, had a funny shape, funny color, and said, do you know what this is? i said, no, i've never seen that before. >> so what could they do? they let william marshall go. the cops had nothing on him. robin hoynes' funeral was a big event in this part of town. and because robin was well known and so well liked, much of the neighborhood attended, and friends and colleagues, except for one, cheryl, the girl who had switched shifts with robin the night the murderer came to call. >> i had heard that they were really upset with me and that they didn't want me at her funeral, and i didn't go. i mean, i felt really sad that i traded hours with her and, you know, that should have maybe been me, and i just felt very guilty for it. >> a few days after robin's murder, the case seemed to be going sideways. william marshall remained only a person of interest, no new leads had emerged, and that odd clue, the piece of foam, was still just a mystery. then came a break. police got a call from an employee at a kentucky fried chicken 30 miles away from the one where robin was killed. he claimed someone in army fatigues wearing a cap, gloves and boots had been casing the story after hours. detective lancaster showed the employee pictures of several suspects who might have been prowling at the kfc that night. >> he pick out william marshall as being the person that was acting suspicious around his business at 11:00, 11:30 at night. >> marshall was put under surveillance and followed for a few days. and where did he go? back to the very same kfc where he was prowling the week before. the employees there wouldn't let marshall in, so he drove off, and cops followed. a few miles later, they pulled him over. >> and after removing him from the car, we found what we felt was the weapon that he had used in our homicide, which was a 7 to 9 inch boning knife in the backpack he had been carrying. >> there was no usable evidence on that knife, but it was the right size and shape, so it looked, to the cops at least, like they had their man. william marshall was arrested. his knife, clothes and boots found in the car were booked into evidence. under california law, detective lancaster had two days -- either charge him or release him. he took the case to the d.a., made his best argument. >> i felt going in we had a good case. you know, maybe a tough case, a circumstantial case, but a good case. >> going in? >> going in. >> coming out? >> coming out i felt like i had been kicked. nobody showed any interest, a complete rejection on prosecution. >> too circumstantial, said the d.a., and no incriminating evidence even on those items seized from marshall's car. marshall was released from jail. his girlfriend, yvonne, picked him up. once again, detective lancaster had to deliver the news to the hoynes family. the only suspect he had was back on the streets. >> maddening. his life goes forward and, you know, robin's is snuffed out and she never gets to meet her potential because of what he did. >> they all suffered, all the hoynes. perhaps mr. hoynes most of all. >> our dad felt like he had not done what he was supposed to do as a father because he didn't protect her. he didn't keep her safe. >> our dad would sit at the edge of his bed and just think about robin and wait for her to walk down the hall every day. >> of course, they didn't know, none of them did, that the solution was sitting right there hidden in plain sight until someone closed the lid and filed it all away. coming up -- nearly 20 years would go by without a break until a fresh pair of eyes focused on one particular photograph and saw something new. >> it couldn't be. it couldn't be. >> when "dateline" continues. it only takes a second for an everyday item to become dangerous. tide pods child-guard pack helps keep your laundry pacs in a safe place and your child safer. to close, twist until it clicks. tide pods child-guard packaging. i order my groceries online now. shingles doesn't care. i keep my social distance. shingles doesn't care. i stay within my family bubble. shingles doesn't care. because if you've had chicken pox, you're already carrying the virus that causes shingles. in fact, about 1 in 3 people will develop shingles, and the risk only increases as you age. so what can protect you against shingles? shingrix protects. now you can protect yourself from shingles with a vaccine proven to be over 90% effective. shingrix is a vaccine used to prevent shingles in adults 50 years and older. shingrix does not protect everyone and is not for those with severe allergic reactions to its ingredients or to a previous dose. an increased risk of guillain-barré syndrome was observed after vaccination with shingrix. the most common side effects are pain, redness, and swelling at the injection site, muscle pain, tiredness, headache, shivering, fever, and upset stomach. talk to your pharmacist or doctor about protecting yourself with shingrix. shingles doesn't care. but we do. hello, i'm dara brown. new york attorney general letitia james announced her run for governor of new york. the inquiry into former governor andrew cuomo will challenge governor kathy hochul. adam kinzinger will not seek re-election for his house seat. the congressman is the second republican who voted to impeach the former president to do so. kinzinger has hinted at a run for higher office in the future. now back to "dateline." welcome back to "dateline." i'm natalie morales. investigators have a person of interest in the murder of 21-year-old be robin hoynes. william marshall. but marshall has an alibi and there isn't enough evidence to bring charges against him. a break in the case would come, but not for another 20 years. here again, keith morrison with "the night before halloween." october 1985, another halloween. once the hoynes' host would have been festive. not anymore. they closed the door, turned out the light. just the word halloween unleashed a wave of grief. the investigation into robin's murder was stalled even though police had a suspect in plain sight. william marshall. and the family groped. >> we had to take comfort in that because we really were probably never going to see any resolution in this. they didn't have enough evidence. >> years passed. there were other cases to solve, new priorities, of course, and for detective lancaster, retirement. >> there are case that is stay with you after your retirement, probably for the rest of your life, at least for me. this was one of them. >> the hoynes family struggled to move on without robin. there were high school graduations, marriages, children, but -- >> the hole never goes away. >> there are times you need to have a tissue handy? >> absolutely. absolutely. >> and then, a decade after robin's murder -- >> our dad committed suicide, and it was devastating for us. it's true he had a terminal illness. he was dying of emphysema but, honestly, he was dying of grief. >> virgin hoynes was just 61. by 2003 the robin hoynes murder case was as cold as they come, 19 halloweens old, buried in the basement of the torrance police department, forgotten. but, that year the department started reviewing unsolved murders and the hoynes case caught the eye of an aggressive deputy d.a. named john lewin who took special pleasure in cracking unsolved cases. >> this is my favorite thing to do. if i won $3 billion tomorrow, i would be coming to work because i'm doing what i love. >> and when lewin read about the original suspect, william marshall -- >> my response was, wow, there's no question this guy did it. i mean, there is just no doubt whatsoever. >> but did he have enough to prove it? the job of finding some new evidence fell to a detective with an unusual pedigree, jim wallace. >> i was in architecture school for a while. i tried design. i have a bachelor's degree in design. >> odd combination but actually it helps, said detective wallace. >> a lot of these cases, this case in particular, are very visual, and i'm inclined that way. i see the kind of structure of the space, the crime scene, and every little detail in the crime scene sticks out to me a little more. >> so wallace looked at the photos and the fragments of evidence still preserved. >> and i said, wow, the anomaly in the room is right here. if i can solve this, i can probably put the whole thing together. >> the anomaly -- well, that would be the puzzling piece of evidence which haunted investigators for almost two decades, that odd oblong hunk of foam. >> i knew it was either going to come from robin, the victim, or it was going to come from the suspect in the case. and once i was comfortable that this didn't come from robin's purse, it didn't come from robin's clothing, it's not part of kentucky fried chicken's restaurant, it didn't belong there. >> which left only one other possibility -- the murderer. wallace pored over the pictures of marshall after he was pulled over and suddenly a light went on. >> he's wearing his clothing still, of course, and he has a pair of work boots. and his work boots, sure enough, i can see just enough from the pants being hiked up that i think i wonder if these are the kind of work boots that have that big fat -- couldn't be. couldn't be. >> could it be the foam? wallace rushed down to the evidence storage room and searched for the box with william marshall's boots inside and, amazingly after two decades, they were still there in a plastic container intact. >> and, sure enough, when i pulled them out, one of the boots had the brown leather casing for that part of the boot that was so important that the foam was missing from the casing. >> come on. >> when i was sitting there looking at that shoe, i've got to tell you, there was a tingle up the back of my neck. >> wallace thought he hit the jackpot. the foam from the kfc appeared to match the remaining foam in william marshall's boot, even the color and curvature looked identical. that foam, he thought, must have fallen from marshall's boot right at the scene of the murder. wallace rushed the news to assistant d.a. john lewin. >> i could have looked at that foam for six years, those shoes, and i never would have put that together. ever. but, you know, jim saw it and then we took it to the fbi. >> the fbi crime lab in virginia, where the foam from marshall's boot and the foam from the kfc would be compared to confirm they matched. it was obvious to the detective that they did. the test really was just a legal routine. no problem. >> i can remember getting the call from the fbi analyst, because my expectation was she's going to tell us i have a match. >> and? it was like a needle going through a balloon. there was a problem. >> she was not willing to say i can't say with any certainty this is from the same shoe because one has phalates and one doesn't. >> phalates? what are those? substances used in plastic to make them more flexible from everything in plastic bags to containers f. that turned up in the foam on marshall's boots but not in the foam at the crime scene, wouldn't that exclude marshall as a suspect? the detective protested they must have gotten in the boots because they were stored in a plastic container all those years. but to scientists, facts are facts, those two pieces of foams did not share the same chemical signature. >> to hear her say one has phalates and one doesn't, i have to tell you, it was devastating. >> not your best day. >> it was what we needed to do something more from 1984. without that connection to the boots i don't think we have a case. coming up, investigators make one last-ditch efforts to talk to their experts. they track them down here leading a surprising life when "dateline" continues. you don't know how much pressure you put on your septic system. but rid-x does. in a 21 month study, scientists proved that rid- x reduces up to 20% of waste build up every month. take the pressure off with rid-x. nurse mariyam sabo knows a moment this pure... ...demands a lotion this pure. new gold bond pure moisture lotion. 24-hour hydration. no parabens, dyes, or fragrances. gold bond. champion your skin. ♪ i'm gonna keep on lovin' you ♪ turns out everyone does sound better in the shower. and it turns out the general is a quality insurance company that's been saving people money for nearly 60 years. for a great low rate, and nearly 60 years of quality coverage, go with the general. introducing new vicks super c and dayquil severe convenience pack . and n[coughs] years of quality coverage, dayquil severe for you... and daily vicks super c for me. vicks super c is a daily supplement to help energize and replenish your body with vitamin c and b vitamins. dayquil severe is a max strength medicine for cold and flu relief. it's the daytime, coughing, aching, stuffy head, fever, power through your day, medicine. someone is feeling better. get your shoes. alright! try the new vicks convenience pack. with relapsing forms of ms... there's a lot to deal with. not just unpredictable relapses. all these other things too. it can all add up. kesimpta is a once-monthly at-home injection... that may help you put these rms challenges in their place. kesimpta was proven superior at reducing the rate of relapses, active lesions, and slowing disability progression vs aubagio. don't take kesimpta if you have hepatitis b, and tell your doctor if you have had it, as it could come back. kesimpta can cause serious side effects, including infections. while no cases of pml were reported in rms clinical trials, it could happen. tell your doctor if you had or plan to have vaccines, or if you are or plan to become pregnant. kesimpta may cause a decrease in some types of antibodies. the most common side effects are upper respiratory tract infection, headache, and injection reactions. ready for an at-home treatment with dramatic results? it's time to ask your doctor about kesimpta. [ eerie music playing ] ready for an at-home treatment with dramatic results? trick or treat! ♪ ♪ he is coming for me... but i'm coming for him. happy halloween michael. just two hours east of los angeles, the mountains rugged, rural, isolated, the perfect place to get lost. it was here that william marshall, suspect in the 1984 murder of robin hoynes had settled. what was he doing way up here in the wilderness? >> he was a firefighter and worked his way up to fire captain here at the station in 2000. >> a fire captain with the california department of forestry, according to dale hutchinson, he was responsible for this station. by the year 2003, marshall had been here almost 15 years, lived quietly in this rustic community known as mountain center. people called him bill, respected him, trusted him to keep them safe. >> he lived right there at the house right behind you. >> terry quinn made friends with marshall soon after he moved in. >> he was a very good person. he was very well respected. he fit in real well up here on the mountains. >> back in torrance, the case detectives had revived after almost 20 years was not fitting together so well. they had hoped that key piece of evidence, the foam, would tie marshall to that long ago crime scene, but the lab wouldn't definitively back it up. without some break, the case would stall again. what to do? well, it was perhaps a long shot, but deputy d.a. john lewin had always figured the alibi marshall got from his old girlfriend, yvonne hargrove, was a little shaky. so he had an idea. what if detectives interviewed both yvonne and marshall on the very same day? would they trip themselves up with divergent stories? >> two teams went out the day that mr. marshall was contacted, one team contacted him, and a second team went to ohio and contacted her. >> yvonne was living in cleveland by then. >> and they say we need to talk to you about something that happened 20 years ago. and my brain went -- and i'm like, okay. so they tell me they're reopening up the one about william and the kfc. they asked me was he with you? i said, yes, the whole night. >> all those years later, yvonne insisted the story she told then and now was absolutely positively true. william marshall's alibi remained rock solid. meanwhile, 2,500 miles away, high in the mountains, detectives pulled up to william marshall's house not knowing what to expect. >> for whatever reason, he was comfortable enough with us to let us in. >> things unfolded slowly. marshall was cooperative and even keeled though in full denial of any guilt whatsoever. >> i had nothing to do with this. no, i wasn't there. you knocked on my door today and you opened up a chapt earp of my life that i thought i had closed. >> then detective wallace tried a different approach. they got talking about shoes, why that distinctive wear pattern on the shoes police seized from marshall back when he was first arrested after the murder of the kfc. >> he did explain to us that his pattern of shoe wear was such that he typically wore out his shoes in this fashion. he wouldn't untie his shoes to get them off, he would kick them off, and the rubbing on the heel, constantly rubbing coming out of the shoe, eventually wears his shoes. and he actually showed us several pairs of shoes that had the exact same pattern of wear. >> then detectives surprised marshall. they revealed the existence of that strange piece of foam found at the crime scene. they told him one of the boots seized from him was so worn it was missing a piece of foam, and the remaining foam in the boot seemed to match it just about perfectly. >> so you're saying that this boot foam -- this is boot foam is what you're telling me? and you're telling me that's out of my boot? >> the cops asked marshall, can we take some pictures of those old worn-out shoes? that's when marshall put on the brakes. >> i had some very negative experiences and stuff with this case and i feel like i'm going down, i'm spiraling away here quick. maybe i should speak with an attorney before we go into anything. >> and with that, the interview was over. interesting, sure, but usable evidence? well, none really. back in cleveland, it hadn't gone so well either, and the cops were wrapping up their meeting with marshall's former girlfriend yvonne hargrove. and then, just before they left, almost as an afterthought, she offered something, a strange story about william, about something he said when she picked him up from the police station when he was first a suspect in robin's murder. >> he's crying and he's saying how am i going to get to heaven? how am i going to get to heaven? he kept saying this over and over and over. >> that's as far as she would offer. it sounds like this is a statement made by somebody who feared because he had done something. >> intriguing but not exactly incriminating. the cops needed more. so wallace returned to the fire captain's house, this time with a search warrant. >> when i came back the second time he got rid of the shoes. the closet was clean. all those shoes were missing. on the back porch he left one pair of shoes, though, the one pair he didn't get rid of, and they had the same pattern of wear. i did collect those and we used those to demonstrate william marshall is someone who would wear his shoes this way. >> more circumstantial evidence but nothing definitively connecting william marshall to the crime. the afterthought from yvonne was interesting but really might have meant nothing. after the visit from the cops yvonne got to doing a little soul-searching. coming up -- >> i know what that thing was on the crime scene floor. >> what was it? did she at long last tell the police? when "dateline" continues. do you struggle with occasional nerve aches in your hands or feet? try nervivenerve relief from the world's #1 selling nerve care company. nervive contains alpha lipoic acid to relieve occasional nerve aches, weakness and discomfort. try nervivenerve relief. do you take aspirin? plain aspirin could be hurting your stomach. new vazalore is the first liquid-filled aspirin capsule clinically shown to cause fewer ulcers than plain aspirin. vazalore is designed to help protect... releasing aspirin after it leaves your stomach... where it is absorbed to give you the benefits of life saving aspirin... to help prevent another heart attack or stroke. heart protection with your stomach in mind. try new liquid-filled vazalore. aspirin made amazing! this halloween, xfinity rewards is offering up some spooky-good perks. try new liquid-filled vazalore. like the chance to win a universal parks & resorts trip to hollywood or orlando to attend halloween horror nights. or xfinity rewards members, get the inside scoop on halloween kills. just say "watch with" into your voice remote for an exclusive live stream with jamie lee curtis. a q&a with me! join for free on the xfinity app. our thanks your rewards. so close to being fired, yet so close to being frozen on the shelf forever. d.a. john lewin and detective wallace needed something, anything, just one piece of solid evidence so they could charge the suspect with robin hoynes' murderer. but what? after cleveland, ohio, yvonne hargrove starting wrestling with her own soul. she thought how williams had given her a beating so severe, she thought he'd kill her and a cold fear set in. if she said anything, would he come after her and finish the job? after all, he alone knew the story when he said to her he might never get to heaven. dangerous knowledge. >> i was thinking, what's going to happen to me. >> because you know. >> right. he's putting a time bomb to me. my life could be in danger, and i'm thinking what do i do with this, of which i did contact an attorney. >> an attorney all those years ago told her to say nothing, stay out of the investigation, so she did, buried it. but now after that visit from the cops, the turmoil was back, gut-wrenching as ever. she needed fresh advice. >> one of the professors that i had was an attorney. i called him, and he said, when they asked you what happened 20 years ago, did you tell them the truth? i said, no, sir, i told them the same story i told them 20 years ago, but it wasn't the truth. he said, you know, maybe you should tell the truth. >> so she picked up the phone and called the torrance p.d. >> and i said i have something that you need to know. what happened 20 years ago with william being at my house was not true. he wasn't at my house that night. >> now here it was, the awful secret she'd kept all those years. >> i said, the next thing is he killed that lady, and he did not get a dime. >> he did it yvonne was his confessor, and now she recited it all, every million dollar russ moment that night before halloween at the kfc. >> yvonne was a force and when she started going, it just sounded credible, and then it was supported by the physical evidence we had which she knew nothing about. >> he did tell her he went out and went to a kentucky fried chicken. he did tell her he wanted to get the money but the employee put it in a drop box and couldn't get the money. he did tell her he stabbed the victim. he did tell her when he couldn't get the money, he slit her throat. >> one more piece. the foam from the crime seen. she knew how it got there. >> i guess he looked at his shoes and all the backs were worn off them. the most crucial moment of his life. that's when the piece of that foam from the back of that boot popped out and was on the floor. >> the foam, the murder, the coverup, yvonne's 20-year secret was finally out. >> when you were telling those things, what was going on in your tummy? >> a feeling of relief that i could finally get it out. >> i would think you would be pretty darn nervous. >> i was. but i was tired. i was tired in my gut. i wanted to be normal again. i wanted my life back. >> then in the mountains a delegation of policemen arrived at the fire station of the popular captain known as bill. >> i was totally surprised when i got the word he had been arrested and even more surprised when i heard what it was for. even to this day, i find it hard to believe. >> word about the arrest traveled to the hoynes' home. >> very exciting. >> relief. >> it sounds terrible but thrilling because you know what? it was the beginning of the ball rolling that he's going to stay in prison for the rest of his life and never get out. >> his trial, 23 years after robin's murder. william marshall was not 46. he arrived in court each day carrying a bible. his troubled youth, early drug addiction, brief rap sheet were decades behind him. this is a man who looked incapable of cold-blooded murder. he said nothing. he just watched john lewin make the case against him. >> william marshall knew before he walked in to the restaurant that night, he knew that robin knew him. so he knew that if he was going to do this crime, he was going to kill her, so this was just a heartless horrific unconscionable crime. >> the motive? drug money, then eliminate the witness, said prosecutor john lewin. marshall had been arrested before robin hoins' murder for pcp, a man who needed cash, who thought he knew where to get it. and then yvonne hargrove told her story, looked over at marshall and his bible, hadn't seen him in over two decades. >> i wanted to walk over to him and say, you hurlt me. i wanted to say you not only hurt this family, but you hurt me. i wasn't allowed. i guess once i gave my testimony, i guess it was a done deal. >> two days later the jury agreed. they found william marshall guilty of first-degree murder. he was sentenced to life in prison. >> i always knew he was going to pay for what he did, but i even mean enough that he pay here on earth. i hope he lives to be 100 and live nas that 6x9 cell. >> robin deserves justice. it's true the trial didn't bring her back, but now robin's murderer is accountable. >> and there's someone else, the woman who traded shifts with robin. all these years she believed the family blamed her fehr it. now finally she learned she was wrong. >> i remember her mom said something to me, that robin was a nice person and that's why she changed hours with me, and she said, and i believe you're a nice person, too, and you would have done the same thing, and that changed everything because i thought, you know what? she's right. i would have. i would have changed hours too. >> how did it feel to be absolved by that family that day? they never, ever blamed me in any way. >> and for yvonne hargrove, the woman who in the end who finally did the right thing, did the hoynes family harbor any resentment toward her for not coming forward all those years. >> i can't remember if it was the older woman, but one of them looked at me and she gave me a little smile and that was enough to let me know i'm okay with them. they sent me a thank-you card of their gratitude. it made me feel good. i think about the young lady because i keep that. >> remembrance of her, and i'm so sorry that happened to her. >> just a few weeks after the trial, it was halloween once again, the always dreaded anniversary of robin's death. but that year -- >> my mom says i guess we need to buy some halloween candy. that might another sound like very much to anyone, but that is like huge, you know, and we did. you know, we do hand out candy now, just things you can't even imagine change in ways that seem very small but really are monumental. >> that's all for this edition of "dateline." i'm natalie morales. thank you for watching. breaking right now on msnbc, the biggest world leaders gathering in person for the first time in more than two years. the gathering just moments ago, the president facing numerous challenges on the world stage, looking to repair some important alliances. >> i think what happened was, to use an english phrase, was clumsy. >> this high-profile meeting with the pope running three times as long as the pontiff's meeting with president trump. 28 million american kids