>> announcer: tonight on all-new "20/20" -- no body. no weapon. but definitely a murder. >> this was a very quick -- and the frantic cleanup. >> announcer: just this week, a bombshell jailhouse confession that could change everything. what really happened to popular teenager brian carrick. who went to work and just vanished. >> it's every parent's worst nightmare. and i guess we're living it. >> announcer: is the right one behind bars? >> there's somebody who knows exactly what happened. >> announcer: the "20/20" exclusive with the man locked up for murder, out of shackles, out only to talk to us. tonight, we're taking you inside

a cold case and cold storage. >> what did you think that circular stain was from? >> announcer: those interrogation tapes. stock boys on the hot seat. and the blood-sniffing crusader who says she can name the real killer and can show what he did. tonight k you solve the mystery on johnsburg road. >> where did he go? here's david muir. good evening. tonight, here, a mystery in the heartland with an explosive new twist. a popular teenager who leaves the house to go to work across the street, at the town grocery store, but he never comes home. what really happened at the back of that store, in the storage cooler, a man behind bars but is he really the man who killed him? and you'll hear from someone else who said he lied to put him

there. all part of the mystery of johnsburg road. here's abc's ryan smith. >> reporter: the village of johnsburg, illinois, the essence of small-town america. a flag-waving heartland, some 50 miles outside of chicago. a conservative community where tradition reigns and nostalgia is embraced. some call this "mayberry of the midwest." >> there's a lot of farms out there, still. some subdivisions. you got the grocery store, bowling alley. very simple, very -- just kind of easy. >> reporter: but johnsburg is also a village with a secret. a lingering 12-year-old unsolved mystery that still has people talking. >> i really can't think of a bigger news story. >> i would say everybody had an opinion. >> i think there's somebody who knows exactly what happened.

>> reporter: what happened to brian carrick, a likable 17-year-old high school junior, who one friday night vanished from inside the grocery store where he worked as a stockboy. just five days before christmas. amanda marrazzo covered brian's disappearance for "the chicago tribune." >> he was excited about christmas, there was no indication for him to run away. >> reporter: his father william carrick, an electrician, says his youngest son was always by his side. >> wherever his dad went, his dad said he'd be in his hip pocket. he was an entrepreneur. sfwlr and he loved val's foods. the village's only grocery store directly across the street from the carrick home. >> you have no idea how smart he was. if you tell him to do one thing one time, say this is what i want you to do. next time, he'll tell you what to do.

>> so, he was a go-getter. >> if there were more people like brian in this country, there will be a beautiful future for america. >> reporter: in johnsburg, everyone knew the carricks. the hardworking irish catholic family with 14 children. brian was the 11th. >> the parents, when they got married said "god give us as many kids as you want to give us, and we'll take them." >> describe the carrick family for me, what were they like? >> all very nice people. one of the sisters said they didn't have the best clothes. and they didn't always have school supplies. but they had a lot of love. >> reporter: that december 20th was brian's day off. but went to val's looking for a co-worker, passing his brother eddie, also a stockboy, on the way. >> eddie was going out to get the carts from the parking lot and brian was walking into the store. he never saw his brother after that. >> reporter: the next day, his mother terry carrick received a troubling phone call. brian hadn't shown up for work. >> she knew her son would never miss work. that was his life was going to that store. >> reporter: she went upstairs he wasn't in bed.

she knew immediately something's wrong. within days johnsburg was reeling in disbelief. this was not the kind of town where people just went missing. >> johnsburg's so safe and such a small, family, church-oriented community and then to have something like this happen is just very hard to take in. >> reporter: supporters gathered at a vigil for brian. walking the same route he walked to work, across johnsburg road. his mother terry, the strong matriarch shaken. >> horror. the torture of not knowing where he is or what happened. that's every parent's worst nightmare and i guess we're living it. >> reporter: as weeks passed, no one knew if brian carrick was dead or alive. >> johnsburg police were involved. illinois state police became involved. the fbi became involved. people were searching the places where brian might go around town. they had the search dogs, they had -- psychics would come to

terry's front door, and try and tell her where he might be. >> reporter: val's foods posted a $25,000 reward. grocer jerry casciaro's daughters, julia and joanne. i think some people would say, "you're putting up $25,000 for somebody who works for them. not a family member but an employee." >> because, you know, the carricks needed it. they didn't have the money. we were desperate to try and find what happened to him. >> reporter: the carricks and the casciaro's, two of johnsburg's most well-known families. friendly for nearly 20 years. almost half of the carrick kids had worked at val's. i understand you have a picture of him in your wallet. >> yeah, definitely. >> reporter: can you show me? >> sure. >> reporter: so, this is some 12 years later -- >> this is a beautiful kid. >> reporter: -- you're still carrying this picture in your wallet. >> right. >> of this young man who worked with you as a stock boy. >> right.

right. >> reporter: high do you carry his picture with you? >> because, to me, he was like a son. >> reporter: an early break in the missing persons case revealed blood evidence in and around the grocery store produce cooler, news no one wanted to hear. drops, spatter, smears, a bloody fingerprint -- brian's blood. what heartbreaking mystery did the family's grocery store hold? what was your reaction when you heard that police found blood in the produce cooler? >> i think then immediately it's like, "well, who did it?" everybody was just like on edge. >> reporter: police quickly turned their attention to the one with no priors. the boss's son. 19-year-old mario. >> are you kidding me sf? >> reporter: you guys are shocked at that point? >> yes, completely shocked. >> mario is one of the nicest, kind, intelligent, funny, just a sweetheart. >> reporter: cops were being to

develop a more sinister profile. >> allegedly was selling dope and i think he coerced my son into working for him and somehow, yeah, things got out of hand. >> there were rumors that there were some things going on at the grocery store. tell me that theory. >> reporter: he would use some of the kids from the grocery store to sell the drugs, brian carrick. and brian carrick, bein' the sweet kid that he is, wouldn't always collect the money. >> reporter: authorities were convinced that the boy who freely gave away pot was a victim of foul play. they believed he was killed over a drug debt he owed mario. the police began to dig into mario. they believed that he was selling drugs. >> i think you know maybe he

smoked pot. i think maybe he and his friends bought and sold it to each other. we're talking about a very small amount. >> reporter: but with no eyewitnesses, no physical evidence tying mario to the crime scene or even a body, the investigation grew cold. and so did the bond between the carricks and the casciaros. >> the relationship had gone sour. and then one day my dad said that mrs. carrick had come in the store and she kind of turned her back to him when he approached her to say hello, and that was the last time she ever spoke to him. >> reporter: but for mario, life was moving on. here he is receiving his degree in finance from illinois state university, three years after brian's disappearance. >> yeah! >> reporter: but for the carricks, no closer to any answers. it was as if time stood still. mario joined the family grocery, worked as a manager, and helped build the business.

>> that was not the only store that he was going to have. it was always going to be two stores, and three stores and four stores. >> reporter: that grand plan would never happen. mario's world was about to collapse around him. a break in the case. this stock boy, shane lamb, would change everything with a tale of violence in the produce cooler the night brian carrick vanished. >> i hit brian a few times. he was bleeding from his mouth. thought i knocked him out. >> where's mario when you're doing this? >> right in the doorway. >> reporter: what did happen to brian carrick? stay with us "i'm 16 and just got my first car" feeling. presenting the buypower card from capital one. redeem earnings toward part or even all of a new chevrolet, buick, gmc or cadillac - with no limits. so every time you use it, you're not just shopping for goods. you're shopping for something great.

learn more at buypowercard.com ♪ if you're struggling with bipolar depression, there are treatment options. ask your doctor if once-a-day latuda, lurasidone hcl, may help you. in clinical studies, latuda has been shown to be effective for many people struggling with bipolar depression. latuda is not for everyone. call your doctor about unusual mood changes, behaviors, or suicidal thoughts. antidepressants can increase these in children, teens, and young adults. elderly dementia patients on latuda have an increased risk of death or stroke. call your doctor about fever, stiff muscles and confusion, as these may be signs of a life-threatening reaction or if you have uncontrollable muscle movements, as these may be permanent. high blood sugar has been seen with latuda and medicines like it, and in extreme cases can lead to coma or death.

other risks include decreased white blood cells, which can be fatal, dizziness on standing, seizures, increased cholesterol, weight, or prolactin, trouble swallowing, and impaired judgment. avoid grapefruit and grapefruit juice. use caution before driving or operating machinery. there are paths to treat bipolar depression. ask your doctor if once-a-day latuda for bipolar depression is right for you. for savings options, visit latuda.com. ♪ good morning, usher! hey! did you know bees communicate through dance? me too... we're practically twins! look for big g cereals with money saving offers

on these breakfast favorites and give your budget a boost. ♪ welcome to the new cricket wireless. just how big is our 4g lte network? bigger than t-mobile, sprint and metropcs. (phone rings.) plans start at just 35 dollars a month. after 5 dollar auto pay credit. cricket. something to smile about. you're playing for more than one million dollars. you're playing for greatness. play monopoly at mcdonald's for your shot at millions of prizes. let's play this game. the game you love is back. ♪ my feet felt so heavy at the they used to get really tired. until i started gellin'. i got dr. scholl's massaging gel insoles. when they're in my shoes, my feet and legs feel less tired. it's like walking on a wave. dr. scholl's massaging gel insoles. i'm a believer!

>> announcer: "20/20" continues, once again, ryan smith. i would like to thank everybody for attending tonight. a toast to prosperity and the future. salud. >> reporter: happy memories for mario and the casciaro clan. older brother eugene's big italian wedding. but good times were in short supply for this family. jerry and maria casciaro, italian immigrants, met and married in the states, realizing

their american dream when they joined with relatives to buy val's foods. >> you know, he didn't have anything given to him. he came to this country, built what he had from the ground up. >> reporter: in an age of superstores, val's thrived in the small town where a night out is spent at a local sports bar or bowling alley or a pizzeria. nearly every family in the village shopped there. so many of the local kids worked there, and for the casciaros, the future was bright. those dreams, now tarnished by tragedy and grisly rumors about missing stock boy brian carrick, believed to have been killed inside the store's produce cooler. >> one of the persistent stories is that brian was killed in the cooler. mario called family from the

city who came in and then dug him up and threw him in a river in iowa. >> it snowballed into these disgusting rumors that -- that he was cut up in our meat department. and then it started becoming that our family was involved in some kind of crime family -- >> reporter: the fbi investigated and dismissed rumors of a mob hit. this case may have remained an unsolved mystery if not for this man. >> this is assistant state's attorney michael combs. >> reporter: also known as mic combs, a tough, hard-edged prosecutor, determined to find justice for the carrick family. 2010 -- a break in the eight-year-old case. prosecutor combs finds a key witness. his name, shane lamb. who is shane lamb? >> shane lamb. he -- he's got a criminal history. he grew up rough. i think he's a very tragic character in all of this. >> reporter: a stock boy at val's who worked alongside brian and mario. a five-time felon with a rap sheet that included attempted murder, at just 14. he'd repeatedly denied knowing anything about brian's disappearance to authorities. now eight years later, in jail

facing up to 12 years on drug charges, he was ready to talk. but first he wanted a deal, and so did prosecutors. >> shame lamb is given immunity from the offense of murder, involuntary manslaughter, concealment of a homicidal death and any other offense resulting in his involvement in the disappearance of brian carrick. >> reporter: with this deal, shane escaped all charges related to brian's death, and a reduced drug sentence. all he had to do to get the deal, tell his story and that led police to mario. >> what exactly did mario tell you? >> pretty much -- talk to brian, try to get the -- intimidate him into getting the money. >> how were you to intimidate him? >> talk to him. he never came out and said, "go kill him," or anything like that. >> reporter: a controversial deal awarded to a man who admits he was the likely killer, and mario was the mastermind. >> according to the prosecutor, mario knew what he was doing.

introducing shane as his enforcer, the intimidator, of his operation. >> reporter: shane was off that night at a party getting high. he says mario called him to come to the store. brian owed him money, and he wanted it back. mario wanted shane to talk to him. it was time for him to pay off. >> i went over there, told brian, "what's up with the money you owe him?" why don't you pay him, you know. we got to arguing. mario said it was getting too loud, go in the produce cooler right there. >> reporter: shane says he demanded the money from brian, but brian resisted. shane lost his temper, and things turned violent. >> i hit brian a few times. he was bleeding from his mouth. >> how hard did you hit him? >> thought i knocked him out. >> where's mario when you're doing this? >> right in the doorway. >> reporter: knocked unconscious, not sure if brian was dead or alive, shane says mario told him to leave the grocery store. >> and he said, "don't worry. i'll handle this." i left. and went back to the party. >> reporter: armed with shane's version of what happened -- prosecutors arrest mario casciaro for killing

family friend brian carrick. a small victory for bill carrick, reminded daily of the store across the street on johnsburg road. a moment terry carrick would not live to see when she died in 2009. for the casciaro family it was a moment of utter disbelief. >> i wanted justice for -- for the carricks. but i -- they got the wrong guy. >> reporter: mario and shane, the mastermind and the muscle, according to the prosecution's theory. though shane says mario never laid a hand on brian, never ordered him hurt, prosecutors insist he's guilty of the rare charge of murder with intimidation. to them, just by uttering the words "talk to him," mario casciaro sicced a weapon of destruction on brian, and was responsible for everything that followed, including brian's murder. had you ever heard of this kind of charge before? >> no.

>> it's very rare. >> reporter: use before? >> from my understanding, it hasn't. >> reporter: an aggressive move. a charge never before used in illinois state history. mario plead not guilty. the case goes to trial. and after 12 hours, jurors were deadlocked, eleven to one, in favor of the prosecution. a hung jury. >> sometimes lay people struggle with the one person being legally accountable for the actions of another. >> reporter: when you learned that it was a hung jury, what were you thinking? >> we were frustrated. >> no, we were frustrated. just like the carricks were. >> reporter: prosecutors went after mario again, vowing to retry him. once again, shane lamb was the prosecution's star witness. prosecutors telling jurors shane lamb was mario's "enforcer," a tool for his "dirty work." in closing arguments, prosecutors branding the pair "mean little delinquents," "criminals who flock together,"

in mario's "drug cartel." so this is a narrative the prosecutors are building so that people can see mario as this dangerous, nefarious figure? >> if you have evidence, then you stick to the facts and you say, "okay, here's his dna. here's his blood. here's, you know, the timeline. we didn't have any of that. >> no. >> so they had to dirty him up a little bit. >> reporter: prosecutors' clever strategy worked. >> he kind of looked like the -- spoiled, rich kid that was trying to be like a little mini-gangster or something. >> the man who didn't say a word throughout two murder trials decided to speak only to 20/20. but why now? did you kill brian carrick? stay with us. you are loved. you are loved a lot.

and in so many ways. and when you're wrapped in the comfort of pampers swaddlers with blanket-like softness and up to 12 hours of protection, all you feel is love. wishing you love, sleep and play. pampers. the answer to treating your dog's fleas and ticks is staring you right in the face. nexgard, from the makers of frontline® plus. it's the only soft, beef-flavored chew that kills both fleas and ticks. vets recommend it. and dogs, well, they're begging for it. nexgard is for dogs only. and hasn't been evaluated for use in pregnant, breeding or lactating dogs. reported side effects include vomiting, dry flaky skin, diarrhea, lethargy and lack of appetite. use with caution in dogs with a history of seizures. recommended by vets. loved by dogs. from the makers of frontline plus. oh wait, oyou got it?falling.... we need nails. with just five minutes' prep, campbell's slow cooker sauces help you cook a real dinner,

right in the middle of real life. and this is the new ♪this is iphone 6 plus. 6. they're the biggest iphones ever made. they're huge. yeah, but their size is just the beginning. even though they're huge. sure, sure. but they could change the way you see the world. oh, that is so huge. they could improve your health. huge! they're the biggest, most powerful iphones ever made. huuuuuuuggggeee! huuuuuuuggggeee! stop it, please. huuuuuuuggggeee! stop it... thank you. ♪ huge.♪ that's why there's a listerine® product for every mouth. one to clean your whole mouth. one for those hard to reach places. one to protect kids mouths from cavities. even one to freshen breath on-the-go. with over 100 years of innovation in oral care... there's a listerine® product for every mouth in your house. for cleaner, healthier mouths go beyond brushing alone.

listerine®. power to your mouth ™. red robin's tavern double burger and bottomless fries is just $6.99. so you can treat a friend to a burger without making him feel emasculated. now, who's your burger daddy? 24 burgers. a million reasons. red robin...yummm

>> announcer: "20/20" continues with the mystery on johnsburg road. here, again, is ryan smith. >> reporter: tonight, mario casciaro sits inside one of the toughest maximum security prisons in the country, menard. over a century old the notorious and the deadly have been held here. remember him?

the serial killer clown, john wayne gacy? he did his time here. and now, it's home for mario casciaro, which is where william carrick believes he belongs. >> everything i heard about these maximum security prisons is bad. he's earned his place. >> reporter: the college graduate and budding grocery store magnate now a convicted murderer shackled and chained to the floor. brian carrick's family believes that you belong here. >> if allegations are repeated over, and over, and over again for, say, seven years, you begin to believe that it's a fact. >> reporter: the carricks believe that you know where brian's body is. >> it's sad that they think that. it's sad that they would ever think something like that. and i really hope that we find brian. >> reporter: a toast to mario before every family meal. >> i'm not a criminal. nobody in my family's ever even

been in handcuffs. i'm the first. and that includes extended family as well. >> reporter: mario says brian carrick was a loyal employee and they had a good relationship. >> he was a good guy. good family. he worked hard. one of my favorite co-workers. >> reporter: 12 year later and mario still remembers december 20th, 2002. just five days before christmas. the store packed with shoppers filling their carts with all the makings of christmas dinner. it was brian's day off but he showed up that evening, around 6:30, asking for another 6:30, asking for another stock boy robert render. >> brian was looking for rob render and had asked me if i'd seen him. and, "hey, where is this guy?" and i -- i paged him, and that was the last time i seen him. >> reporter: after seeing brian, mario says he picked up a pizza nearby, sharing it with employees in the break room clear across the other side of the store from the produce

cooler, that's his alibi. mario says he helped close the store, as usual, at 8:00. both the defense and prosecutors believe brian was murdered before closing time. did you kill brian carrick? >> absolutely not. >> reporter: are you responsible in any way for his death? >> no. >> reporter: as for the prosecution's claims that the man who put him in prison with his testimony, shane lamb, was called to the store that night to talk to brian? so this is important because police believed at some time you call shane lamb, did you ever call him? >> no. we actually gave my phone records and showed them that there was no call. >> reporter: on your urging of, "talk to him," has an altercation with brian carrick, punches him a few times, lays him out. you tell shane, "go. i'll take care of this." any truth to that? >> not at all. didn't even see shane in the building that evening. why would i say, "yeah, buddy. let me take care of this for you." i don't even know that kid. "let me just take care of a murder for you."

be serious, you know what i mean. >> reporter: he questions why anyone would believe he'd take a murder rap for shane lamb who'd only worked at the store for a few months after a two-year stint in juvie for attempted murder. but what about the witnesses, did you ever sell drugs? >> there were times that -- when i was smoking pot, that i would, i guess, sell people pot out of my personal stash. it wasn't, like, a criminal enterprise. >> reporter: did brian ever sell pot for you? >> no. >> reporter: did brian ever owe you money for selling pot? >> no. no. >> reporter: so this claim about him owing you $400-500, and that's why you had shane talk to him? >> it's all made up. they took something that was very small, small amounts of marijuana and made it seem like it was a huge criminal enterprise. they actually went so far as to say i was a drug cartel and kingpin. that's significantly different than smoking some weed with your friends. >> reporter: former local reporter sarah strzalka agrees.

>> there were multiple people who got up on the stand and said that they had bought, you know, pot from brian or bought pot from mario, or whatever it may have been. but, this wasn't a cartel. it wasn't some big drug empire, it was high school kids buying little pot here and there. >> reporter: you didn't testify at your trial. how do you feel about that decision now? >> i think it was the wrong decision. i wanted to do it at the time. i was just advised not to. >> reporter: his future was in the jury's hands, they never heard from him, that may have cost him. the verdict. what's going through your mind as you're waiting for that verdict in the second trial? >> "what is taking so long? what are they thinking about? what could they possibly have found to be credible that they've seen?" >> reporter: did you think, at that point, you were going home with your family? >> yeah. sure did. >> reporter: how firm was your belief that you were going home? >> 99. >> reporter: going home wouldn't

be in the cards. a guilty verdict, mario's mother's outrage caught by local news cameras. >> this is a cover up, big time. >> his family sobbed. his father wailed. mario was confident the whole time, his head was up. and then he just drops his head. he was shocked. thought he would never be convicted. there's no physical evidence. >> it was heart-wrenching. it was -- it was if mario had died. >> reporter: can you make it >> i don't want to. if i have to, i will find a way. but i don't want to sit here every day thinking about how did i get here. i don't have any answers. you know what i mean. >> reporter: enter this woman. she's uncovered a detail never brought to trial, something hidden behind a ceiling tile. what do you think of mario's story. we're on twitter tonight. ryan answering your questions as

his report unfolds here tonight. and next, a piece of evidence found in the ceiling of that store. >> announcer: next, a new suspect enters the picture as we follow a trial of blood and a trial of a knife. >> comes up behind him like this and cuts his throats. the all new, head turning cadillac ats coupe. it's irresistible. ♪

every time you take advil you're taking the medicine doctors recommend most for joint pain. more than the medicine in aleve or tylenol. the medicine in advil is the number one doctor recommendation for joint pain. relief doesn't get any better than this. advil so did you hear the new iphone is out? i'm getting one! sprint is offering this exclusive new plan with unlimited data. the plan is only $50 a month! $50? unlimited iphone! [glass shattering] so should we eat? the new sprint simply unlimited plan,

exclusively for iphone 6. unlimited data, talk and text for just $50 a month. switch to sprint and we'll buy out your contract. it's the best value in wireless.

dowlower... that's more like it! petsmart's prices on your favorite food brands just got lower! shop a wide assortment of food and save up to $8 on your favorite dog & cat food brands. at petsmart®.

>> announcer: once again, "20/20," and ryan smith. >> reporter: they walk in silent protest. a family crusade to free 31-year-old loved one, mario, sentenced last november to 26 years for murder. >> there was no physical evidence, no dna, no witnesses,

and no motive. >> when you are innocent, you are going to fight until the very end. because you know you're innocent. and we're going to fight till the very end, because we're 100% behind him. >> reporter: and that's why they hired this gladiator, kathleen zellner, a high-powered attorney, to appeal his case. her reputation overturning convictions and solving cases. she's uncovered what she believes are secrets long tucked away inside the family grocery store. >> i believe we have an excellent chance of this. this'll just be reversed outright. >> reporter: according to kathleen, the trail of evidence potentially so explosive it may set mario free. she believed the evidence leads not to mario, not to shane lamb, but to one man, rob render, an early suspect in the case, that stock boy brian accused of stealing alcohol from the grocery store and the one brian was looking for the day he vanished.

>> what do we know about rob render? >> another troubled soul, he's just had a lot of problems, a lot of drugs. >> reporter: for kathleen, the case begins with the physical evidence. the blood at the crime scene, rob render's blood was there, and his was the only blood that was ever found aside from brian's. >> we know that they had an altercation because both of their blood is right there at the scene. >> reporter: for her, the crime scene tells the story. look at these photo exhibits. while brian's blood is in the hallway leading to the cooler, rob render's bloody fingerprint is on the cooler door handle and inside the door, more of rob render's blood. when police questioned rob, he insisted he wasn't there. >> i didn't do anything and, i don't know anything. and it's like, you know? >> reporter: they asked rob if he wasn't there, why was his blood? >> maybe i cut my finger.

hey, who knows? maybe i bit my nails so bad, because i do, that it bled a little bit and i put my thumb on the door. >> there's no way that this amount of blood could have been left by rob render by biting his nails. you'd have to be a hemophiliac. you'd had to have a clotting disorder. >> reporter: and for kathleen, the motive, brian turned in rob for stealing booze, ridiculed him at work for being weak and, according to jacob kepple, another stock boy at the store. >> brian had told rob, "if you don't have it by friday, it's 60." and to me, that meant, "if you don't have the $30 you owe me for weed by friday, then it's double." >> reporter: next, opportunity, where was rob render that night? kathleen contends that other employees said rob was nowhere to be found for nearly two hours. but according to rob -- >> i was probably stoned. >> that night? >> i'm sure. i was 17 years old. that's all i ever did.

but i never, ever, left work! you know, maybe they were looking for me and they couldn't find me. maybe i was stuck in an aisle somewhere, maybe, you know, maybe i went on break. i'm telling ya, i never left the store. >> reporter: but maybe he knows more than he's telling. that's what police thought. he told a friend there was a fight in the cooler and that led them to the crime scene. >> honestly, that's what led us over to the cooler and led us to the blood. >> nobody else has said that. that there was a fight in the cooler. nobody else knew where the scene of the crime was. >> reporter: a detail kathleen believes only the killer would know. she says rob also tried to cover his tracks, mopping up the produce cooler that night and being on the scene the next morning when co-owner, jerry casciaro, noticed a pool of red-tinted water. what did you think that circular stain was? what did you think it was from? >> at the time actually i only thought it was hawaiian punch. >> reporter: okay. >> i got a little hot under my collar and i said, "okay, you. clean it up. you clean it up."

the "you, clean it up" was rob render. >> reporter: and kathleen has a witness, an employee at the grocery store when brian disappeared, who could rock the prosecution's case with explosive claims. what did this new witness have to say? >> the new witness said that render had made a statement to him just a week before brian disappeared that he was very angry with brian, and that he was going to jump him with a weapon. >> reporter: that matches her version of events. kathleen says the fatal blow wasn't from a punch as shane lamb confessed, but from a knife. >> tell me what you believe happened between brian and rob render. >> i believe that render comes up behind him like this and cuts his throat. them, i believe, that brian starts falling forward and render grabs the door and that's why his print is on the door and then he pushes him like this. then he scrapes against -- that's why the transfer blood is

there. the attack is in the hallway. we're all familiar with the blood evidence. >> reporter: and acting on a tip from this witness, kathleen's investigators, finding a piece of evidence in the police report, a pair of soiled underwear, with a brownish red color. kathleen thinks it is blood. mario's attorney kathleen zellner believes that what may have happened in this ladies' bathroom could blow this case wide open. a stock boy, coming into this bathroom about a month after brian disappeared, saw that there was a leak in this bathroom and saw that it lead up to this panel. so, he stepped on this toiled lifted up this panel, and found a pair of men's underwear, size small. >> reporter: a size similar to rob, the underwear, handed over to the police. but kathleen says it wasn't entered into the evidence log and never made it to trial. >> that is a huge bombshell and that's why we want to have dna testing. we want to confirm if that was

his underwear. because if that's got render's blood on it and carrick's blood on it, that is all you need to know about who committed the murder. >> reporter: so we don't know that for sure. you just need to check it out to see if that is part of the picture? >> yes. >> reporter: prosecutor combs admitted to 20/20 that the underwear was not tested but stated both the police report and the witness were available to mario's defense lawyer before trial. >> unfortunately for you, the evidence points at you. almost all of it points at you rob. >> reporter: rob wasn't let off scot-free. police charged him with concealing brian's murder, but within a month dropped the case believing he wasn't involved. rob render never told his story in court. struggling with drug issues for years, he overdosed on a cocktail of heroin and cocaine and died in 2012, just months before mario's second trial. mindy lindholm, rob's older sister, passionately defends her brother. she claims he would never hurt anyone. >> the premise that my brother could have possibly killed brian over $30, or over him telling on him, or anything, is ridiculous

to me. my brother having an explosive temper is absolutely ridiculous. >> reporter: and she accuses kathleen zellner of scapegoating her dead brother. >> i asked him, you know, what he knew about it and, you know, he said he wasn't there, you know, and he didn't know what happened. >> reporter: i'm sure prosecutors will say this is a classic case of blaming the dead guy. >> to me, that's meaningless, to say, "blame the dead guy." doesn't mean dead guys didn't commit murders. the only person that really disliked brian carrick is render. the only person that owes money to brian carrick is render. the only person who's ever described wanting to jump him with a weapon is render. and the only person in that back hallway is render. >> reporter: next, the state's star witness, shane lamb, the man who put mario casciaro behind bars does a shocking

about-face. stay with us. what's happened to snacking? how did it become absent-mindedly eating one after the next? we are a creamy cheese that still believes in savoring our food. ♪ the laughing cow. reinvent snacking.

smooth, and creamy... you'll never know it's sugar free. and find it in all the indulgent caramel flavors you love. werther's original sugar free. well, it's been the number one soup in america.soup? (slurp) (slurp) (slurp) (slurp) for four generations (family laughs) (gong) campbell's! m'm! m'm! good!

we thought our cable internet was fast. but, our uploads are half the speeds of our downloads so our internet is really half-fast. so half-fast. someone did a half-fast job of posting our vacation pics. when i post my slow jams, i'm a little half-fast. totally half-fast. stop living with half-fast internet. only verizon fios comes with speedmatch - uploads as fast as downloads. so his homework won't be so half-fast. that is up to him. >> announcer: now, one more exclusive interview tonight. this time, the man whose own

words helped put that grocery store stock boy behind bars. right here on "20/20," he changes his story and here again is ryan smith. >> reporter: just this week, a dramatic development in the mario casciaro case. the man at the center -- the state's star witness whose testimony helped send mario to prison, now says it was all a lie. just 72 hours ago, shane lamb sat down exclusively with "20/20" with a stunning confession. why are you coming forward now? >> because i -- mario's in there for 26 years for something he didn't do. i didn't have anything to do with this. mario didn't have anything to do with this. he doesn't deserve to be in prison. >> reporter: and it's safe to say that he's serving 26 years in a maximum security prison because of your testimony? >> that's right. >> reporter: he said he was coerced by a prosecutor

hell-bent on putting mario behind bars. what do you want to say about your testimony today? >> all of it was false. every single thing, the state's attorney set it up. >> reporter: he's talking about assistant state's attorney michael combs saying he forced him to place mario at the crime scene to get that immunity deal. the one to avoid being charged in brian carrick's death. shane says his back was against the wall. >> i was arrested for cocaine charges. my offer was 12 years. they said that i'd be -- indicted for murder if i didn't >> reporter: and it came down to him or rob render. >> he said rob render was in lake county jail. if i didn't want to talk to them, that they're going to go to rob render next. >> reporter: so you believed that they were either going to feed a story to rob render that he was going to tell about his involvement or mario's involvement. >> right. >> reporter: and whoever took the deal first. >> exact -- yeah. 100% that's how i felt. >> reporter: here he is giving his statement. but according to shane, what you don't see before this point, before the cameras roll, he makes allegations that combs sat

him down for an hour without his lawyer. telling him what to say, point by point. >> reporter: on december 20th, 2002, mario casciaro never called you to say, "come to the store and talk to brian carrick because he owes me money." >> never. >> reporter: and you weren't his enforcer? >> no. >> reporter: did you guys ever get into a fight? >> no. >> reporter: you never punched him two or three times knocking him unconscious? >> never. >> reporter: and then mario never said to you, "get out of here. i'll take care of this." >> never. never happened. >> shane lamb has a lengthy rap sheet. people are going to say, how can we believe him? >> they believe me enough to use my testimony to put him away. but now, since i'm telling the truth now they're going to say i'm lying. >> reporter: if shane is to believe, why would a prosecutor risk so much? why would he put his career on the line threatening you just to

put mario in prison? >> a lot of people don't like mario for some reason in law enforcement. >> reporter: that's a question we put to mario himself. police talked about how you were arrogant talking to them. >> i don't think i'm arrogant. >> this isn't a popularity contest. this isn't the senior prom. >> reporter: the state's attorney's office wouldn't go on camera because the case is on appeal. in a statement to 20/20 today, prosecutor combs denied coaching shane lamb out of the presence of his lawyer, "calling it unworthy of belief, untrue and far fetched." you know, as i hear you today, i think, "what do you have to gain from all this?" >> i have absolutely nothing to gain. the only thing that can -- only thing that can happen to me right now is them recharging me for murder. i have everything to lose right now. >> reporter: so you have nothing to gain, everything to lose. is that why you think people should believe you? >> 100% they should believe me. it's the truth.

>> reporter: how does this change your defense of mario? >> it dramatically changes it. i mean, i think, you know, the underwear that's been discovered, the witness statement about render's plan to attack brian carrick, combined with shane lamb recanting everything, he was the whole case. i mean, he was the only person that was responsible for mario being convicted. >> reporter: but, then, who killed brian carrick? all three stock boys tell a different story. shane lamb now says he was never at the store that day. no co-workers place him there, either. mario casciaro claims he was eating pizza. before his death, rob render proclaimed his innocence. and brian carrick's body has never been found. >> where'd he go? people don't disappear. people don't just get sucked up and disappear. and that's the part that -- that's why we're talking about it. it -- it's so unfair to that family, that they still don't really, really know.

>> reporter: but for shane lamb, one thing is clear -- he is willing to spend the rest of his life in prison so that mario doesn't have to. >> he's in menard right now, one of the worst prisons in illinois for 26 years. and i just feel like -- they let somebody make up testimony to get him locked up for 26 years. and he's sitting there, and he can't do anything about it. i'm not going to have it on my chest anymore. >> reporter: you were the one who put him in menard. >> i was. but i was following what they wanted me to say. they just wanted to close the case. >> reporter: it seems like this weighed heavily on you. >> it did. i don't want to be the reason that he's doing 26 years. if you know mario is watching this, i just want to tell him i'm sorry, his family that i'm sorry. >> reporter: if you feel so deeply about it now, where was that feeling when you were telling the story that put him in prison? >> at first, you know, i don't care how tough you think you

are. you know, it doesn't seem real until somebody gets convicted. >> i'm happy that he's finally telling the truth. i wish he would have done it at the trial so that way i wouldn't -- had to been subjected to this, because this changes your whole life. >> reporter: are you losing hope? >> when you sit in here -- it's hard to -- it's hard to be optimistic, you know? every day that goes by is another day that i'm not with my family. my dad's 79 years old. i don't know how much longer he has left. and every day that goes by, i'm missing out on that. >> reporter: missing out on your family. >> we lost brian. we're not going to get him back, um, and then the only thing the only thing i can hope for is that i'll meet him again someplace. >> reporter: two families, in pain and seeking justice for their loved ones, but has justice been served?

where brian carrick is remains the mystery on johnsburg road. for very dry skin, basic moisturization isn't enough. you need healing. the only lotion with healing micro-droplets of vaseline jelly, new vaseline intensive care relieves very dry skin from the first application and deeply moisturizes to heal it in just 5 days. clinically proven. skin healed in just 5 days. that's the healing power of vaseline. where the reward was that what if tnew car smelledit card and the freedom of the open road? a card that gave you that "i'm 16 and just got my first car" feeling.

presenting the buypower card from capital one. redeem earnings toward part or even all of a new chevrolet, buick, gmc or cadillac - with no limits. so every time you use it, you're not just shopping for goods. you're shopping for something great. learn more at buypowercard.com i've been claritin clear for 8 days. at the first sign of your allergies, doctors recommended taking one claritin every day of your allergy season for continuous relief. 21 days! 14 days of continuous relief. live claritin clear. every day. is back and better than ever, starting at just $9.99. say yes to bowl after never ending bowl of your favorite pasta. and more yes to savory new sauces. like velvety roasted mushroom alfredo and spicy three meat, plus toppings like crispy chicken fritta. never ending pasta bowl, your favorite pasta, garden salad, and fresh baked breadsticks. it's all unlimited starting at $9.99, but just for a limited time.

only at olive garden, we're all family here. enjoy unlimited soup, salad and breadsticks lunch just $6.99. wewhere what we saywireless. is what you pay. like 5 lines for 100 bucks a month. that's taxes and fees included. switch now and get 5 for 100. all in. cricket. something to smile about. >> up next a teen aimer is injured in a crash along the

banks of the schuylkill and health officials reveal t >> and good evening. looking live at stormtracker 6 double scan tonight a soggy start to the weekend. we'll get underway shortly for most of us. tonight, although heavy rain is on the way we know the