you spent hours and hours basically on this street corner. >> he was talking about blondes. he liked blondes. that's when i decided to go really blonde. >> i had to, you know, attract him. >> catch his eye? >> catch his eye. >> but it's not what you think. tonight on "20/20," how far would you go for your child? this far? >> doing things that i think most people would think are borderline heroic. >> or maybe borderline crazy. cooking up an outrageous undercover sting for a year and a half trying to prove her son is innocent of murder. >> she is what keeps me going. >> you believe the police have arrested the wrong man? >> i know it. >> and to prove it, she is trying to take down the juror she says lied and helped put her son behind bars. >> just give me my son.

>> losing 30 pounds, dyeing her hair to woo him. >> low cut blouse, push-up bra, high heels. secretly recording, trying to catch him. >> and not just the juror putting the prosecutor in her crosshairs. >> i have never lost a homicide case. >> oh, god. you know why? because she is a cheater. >> just weeks ago a bombshell game changer for the mother who put her own life on hold to live a double life for her son. is there any way you're blinded by your mother's love? >> i have been begging for a fair trial. just give me a fair trial. >> undercover mother. i'm elizabeth vargas and this is "20/20." here's "nightline"'s juju chang. >> good morning. >> are you ready? >> i am.

rikers, here we go. >> rikers here we come. what a cheery place to visit huh? >> reporter: doreen quinn giuliano has become all too familiar with one of the country's most dangerous and notorious jails. >> it's out of control. it's um, very violent between the inmates and the guards. you don't know who to trust. >> reporter: every week, she makes the hour-long drive from her home in brooklyn to rikers island to see her son john. >> john doesn't belong here. >> where does he belong? >> home. >> reporter: but in 2005, a jury jury convicted john guica of murder, sending him away for 25 years to life. >> does it ever cross your mind that maybe john did have something to do with it? >> no. i'm 100% sure he did not. >> how can you be 100% sure? >> well, the facts. just follow the facts. >> there's part of me that's sympathetic to doreen giuliano, and i almost admire the fact that she stood by him to this point.

but john giuca is not the victim but john guica is not the victim in this case. it's mark fisher. >> reporter: it was columbus day weekend, 2003. 19-year old college student mark fisher is taking a long weekend a break from the books and classes. wanting to blow off some steam, he heads to the big apple to explore the hopping bar scene on manhattan's upper east side. >> it had to be tremendously exciting for a guy from suburban new jersey. he's going to big city for the first time, and there are going to be some girls there he knows from school. >> reporter: that school fairfield university where fisher, a sophomore, is an athlete on the dean's list studying to become an accountant. >> mark fisher was every parent's dream. a big strapping, good-looking student-athlete, prom king in his high school, a phenomenal football player. >> reporter: but on that night, mark fisher has no interest in running defensive plays or crunching numbers. he's just looking to have a good time. >> mark runs into a girl that he goes to school with. she brings a lot of her friends

with her. >> reporter: there's one pretty blonde he's got his eye on. they bond over a couple slices of pepperoni. >> he was following her wherever she went that night. >> reporter: but what started as an innocent night on the town, soon takes a different turn, after the twosome meets tommy saleh and his buddies. >> a bunch of us went to these bars on like the upper east side. >> a bunch of guys. >> a bunch of guys, um. >> cruising for chicks. >> yeah. >> reporter: "cruising for chicks" along with him that night his wingman from high school, john guica. >> best friends? >> yeah. hang out every day, um, weekends. >> reporter: they try and fail to score some drinks. >> fake id's didn't make it. >> no. >> some members of the group were unable to get into the bars. >> reporter: so, 20-year old >> reporter: so 20-year-old john guica comes up with a plan. >> he says, "my parents are away for the weekend. why don't we go to my house and have a party?" >> this was an impromptu party, this was not something that was planned, this was something that just happened.

>> reporter: their journey that night will take them from trendy bars of new york's upper east side -- across the fabled brooklyn bridge -- where mark fisher has no idea what he's about to get himself into. >> why was it decided to go to john giuca's house? >> his mom was away. he had a big house. it was like the easy choice. >> so it was a little bit like, the cat's away, the mice will play? >> yeah. >> i was in florida on a weekend vacation with my husband. >> and john decided to throw an impromptu party. >> i mean, there was a few kids that got stranded in manhattan and had no place to go. >> reporter: one of those stranded kids is mark fisher who now is not only enamored -- he's hammered. according do -- to tommy saleh, fisher is intoxicated, strapped for cash and has no way to get back home to new jersey. >> i just remember john saying, just come with us. >> so this kid you just met, pretty much out of it. >> yeah. >> didn't have money. let's just take him home and let him sleep it off? >> yeah, i'm assuming he was friends one of the girls or something like that.

>> and he figured he'll bring them here to my house, get some beers, and be -- young adults, you know teenagers. >> drinking. >> drinking. i'm sure they were smoking also. >> smoking weed? >> yes. >> and yet, that impromptu party turned into, perhaps, one of the biggest mistakes of his life. >> oh, yeah. yeah. absolutely. >> reporter: doreen says one of those mistakes her son's decision to invite neighborhood "bad apple," antonio russo known for his long dreadlocks and a penchant for picking fights. >> so tell me about antonio russo. >> he was a bit of a wild child. he was younger than all the other boys. >> he was more of a street kid, he didn't have the support system at home that john giuca and many of john's other friends had. >> he's known to be a marijuana dealer. >> reporter: antonio russo, aka tweed, is said to supply the weed. >> at one point after mark had been at this house for about an hour or so it's believed that john giuca basically accused him

of being a mooch. he was drinking their beer, he was smoking their pot. he wasn't bucking up. >> reporter: according to witnesses, guica thought it was time for the mooching mark fisher to pay up. >> shortly after 5:00 a.m., mark fisher went to an atm machine and purchased a six-pack of beer. >> reporter: what happens over the next hour, depends on whom you talk to at the party. but somehow, in those early morning hours, mark fisher the handsome college student out for a night on the town stumbles away from the party. two blocks away to argyle road, and winds up dead. >> i can tell you that our detectives, when they arrived at the scene, they found a male white prone obviously the victim of several gun shots. there was some trauma to his face. >> reporter: the strapping 6'3" 205-pound former football player from new jersey is found shot five times in the back lying on a blanket from giuca's home. >> when you hear it's a kid from new jersey right away, you're

saying, "what's wrong here, and how did this person end up here?" is this some sort of drug deal gone bad, is this some sort of a domestic issue? coming up, the mystery. >> mark fisher's body is found almost in front of the house of one of the other partygoers. >> reporter: the motive. >> it was very frustrating because we were unaccustomed to seeing that kind of coordinated coverup. >> reporter: and a mother's unwavering belief in her son's innocence. >> john was a mess. he said, mark fisher was a good guy, and he was devastated. >> reporter: stay with us. thing rheumatiod arthritis. before you and your rheumatologist move to another treatment, ask if xeljanz xr is right for you. xeljanz xr is a once-daily pill for adults with moderate to severe ra for whom methotrexate did not work well. it can reduce pain, swelling and further joint damage, even without methotrexate.

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2003, when mark fisher is discovered dead. he'd been viciously beaten shot five times, after withdrawing 20 bucks from a local atm. his senseless murder immediately sends the new york tabloids into a lather. >> this is not your typical murder case. this is a very handsome, you know, football player -- which makes for a nice headline. and sells papers, right? >> reporter: the tabloids dub fisher's murder "the grid kid slaying" short for grid-iron. the all-american athlete from a well to do, bucolic, new jersey suburb who somehow found himself too far from home. >> they painted mark fisher as the boy next door that was like a lamb that wandered into the den of wolves. >> reporter: that den? doreen giuliano's home. and those wolves? authorities say, some of those kids who show up at her son's after-hours party. >> you got a call? >> i got a call from john. >> and what did he say? >> he said, "ma, you need to

come home. and i said, "is everything okay? and he said, "you -- you need to come home." >> and, so, you get home, frantic. what's the scene here? >> the press was on my lawn. >> already? >> yeah, and detectives were on my porch. >> reporter: why hers? because remember her son, john giuca, was the host of that impromptu, after hours party. but doreen claims there is little to implicate her son. no gun was ever recovered, no fingerprints, no dna. the only piece of evidence tying fisher to the giuca home -- >> mark fisher was found -- lying on top of what turned out to be your blanket. >> yes. >> what do you make of that? >> you know, mark fisher fell asleep on the sofa. and then in the morning he took the blanket with him. >> reporter: she claims that is not nearly enough to implicate her son, j j j j j j college for, of all things,

criminal law. >> what did he want to do? >> well, initially he wanted to be a detective. >> ironic. >> yeah, i know. >> besides wanting to get into law enforcement, john had other aspirations, as well. he was taking acting classes, and he had actually appeared in "school of rock." >> reporter: that's giuca, "the wannabe actor," pushing past actress joan cusack. >> we used to call him "shady" because he had bleached blonde hair just like eminem. ♪ >> did he have that kind of rough street image that eminem has? >> no. john came from, you know money, catholic high school. didn't grow up in the worst area. >> it wasn't a trailer park in 8 mile? >> no, it was a victorian home in brooklyn, you know? >> give me a sense of the neighborhood. >> old victorian. historic. >> not your classic new york city neighborhood. >> no. no. it's off the beaten path. >> a little bit. so where did all of your son's friends live in relation to here? >> in these houses.

>> reporter: and it's some of those friends the cops are now keenly interested in. one of them is that boy who supplied weed, 17-year-old antonio russo, aka, tweed. police say almost immediately, they want to talk to the local pot pusher. turns out, the morning of fisher's murder, russo suddenly decides to chop off those trademark locks. >> he had dreadlocks that he had cultivated for years, so for him to get them sheared was very suspect and then he takes off for california a couple of days later. >> reporter: police wonder why the sudden disappearing act? >> that certainly makes him the prime suspect. >> reporter: and there's someone else cops are keeping their eye on. >> that's albert cleary's house. >> this is albert cleary's house. >> reporter: albert cleary he's john giuca's childhood friend who lived just two blocks away on argyle road. it's just steps away from where police found mark fisher's body. >> albert cleary becomes a prime suspect because he has an active case in the bronx where he was

involved in a pretty vicious beating of a person laying on the ground. >> reporter: police say everyone at the party is a person of interest, but with no hard evidence, cops say they were hitting a brick wall. >> it became a case of who told who, what and when. and everything was hearsay. >> reporter: the investigation stalls out for days, weeks, and then months. so mark fisher's grieving and frustrated parents turn up the heat, offering a reward for any information about their son's death. >> it's over a year already. it could have been anybody, anyone hurting him. >> reporter: that's when an aggressive, rising star prosecutor anna- sigga nicolazzi gets assigned to the case. >> we liked working with her. we thought she was a bulldog. >> how many people did you interview? >> over 100. well over 100. >> reporter: nicolazzi employs a tactic often used in organized crime cases forcing witnesses including giuca's friends to testify before the grand jury. she squeezes those friends to

build a narrative. >> there were two witnesses who said that john giuca put russo up to the killing. >> reporter: first, albert cleary, that one time suspect, now turned state's witness. then, there's giuca's own girlfriend, lauren calciano. both say giuca told them he was the one who supplied the gun that killed mark fisher. >> one of the things that made this case so powerful was that you had his longtime friend, one of his best friends and his girlfriend at the time testify against him for the prosecution. >> reporter: john giuca is put on trial for the murder of mark fisher as is that drug dealer who cut off his dreadlocks, antonio russo. at trial, prosecutors paint a picture of two neighborhood thugs part of a wannabe gang called the "ghetto mafia" out to get street cred by scoring a kill. >> john was made out to be a young tony soprano, and that his

crew were like "the sopranos." >> i'm the one who calls the [ bleep ] shots. >> reporter: the "ghetto mafia" motive is the crux of the prosecution's case against doreen's son. >> that was a joke, juju. that was such a joke. >> they said that john was the boss or the captain and that you were capos. >> yeah. >> were you a capo? >> i wasn't a capo, no. i was in college. i was going to school for engineering. >> reporter: but, the prosecutor has an ace up her sleeve -- a jail-house snitch by the name john avitto who had approached the ambitious ada with a story to tell. >> he's the last witness. astr avitto meets john giuca in rikers island. and according to avitto, john giuca elaborates on how he killed mark fisher. >> reporter: avitto testifies that his prison mate told him he pistol whipped mark fisher, and then his buddy antonio russo then shot him dead. >> this was an extremely

dramatic moment at the trial. nobody saw it coming. >> reporter: justice is swift. it takes a jury a day and a half to convict russo. for giuca, it's only a matter of hours. >> reporter: both are found guilty of murder and sentenced to 25-years to life. >> what was your reaction to the fact that they jury came back with a verdict in two hours? >> something was wrong. >> reporter: coming up, in a desperate attempt to prove her son's innocence, doreen undergoes a radical transformation. >> why did you wear a burka? >> reporter: her intricate plot that involved wearing outlandish disguises and changing her appearance. >> you knew he liked blondes? >> he loves blondes. >> reporter: who is her target? next. ♪ if you have moderate to severe plaque psoriasis, little things can be a big deal. that's why there's otezla. otezla is not an injection or a cream. it's a pill that treats psoriasis differently. with otezla, 75% clearer skin is achievable after just 4 months, ...

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>> reporter: john giuca is sentenced to 25 years to life for the "grid kid slaying" of college football player mark fisher. >> it was a joke of a trial. >> reporter: outraged by her son's guilty verdict, john giuca's mother, doreen quinn giuliano, decides to take action immediately focusing on the jurors who so quickly convicted her son. >> she was crazed with hysteria, and terrified for her son's future. >> reporter: it's fair to say what she does next, few mothers would ever consider. >> what made you decide to go undercover? >> a mutual friend of john's who was in the audience, recognized one of the jurors.

the guy with the baldy head. >> reporter: doreen believes that if that bald juror knew anyone involved in the trial, especially the witnesses, it should have disqualified him as a juror. >> the key point here is less about how much did he know about these people, and more did he intentionally lie to get on the jury. >> who was juror number eight? >> juror eight was jason allo. he knew my son's friends. >> reporter: could she somehow get him to admit that he should never have been on that jury? >> he committed very serious juror misconduct. >> reporter: doreen, who at the time had been married for 17 years, confides the details of her audacious plan to her husband, giuca's stepfather. >> he didn't want me to do it, honestly. he said, no, no, no. >> you went to a tanning booth. >> yes. i just was trying to knock off some years. >> reporter: these pictures of

her transformation were taken for a "vanity fair" magazine shoot. >> i bought a whole new wardrobe. you know, low-cut blouses, push-up bra, high heels that i had to practice walking in 'cause i wasn't good at it. >> this is not how you're dressed today. >> no. no. i'm pretty conservative. >> you were wearing lots of makeup? >> lots of makeup. hi i had to, you know, try to attract him. >> you became your own private investigator. >> i did. sitting there for hours. you just can't take your eye off the prize. >> and you called him "the target." >> i did call him "the target." yeah. >> reporter: for months, doreen stakes out "the target's" every move on this corner in bensonhurst, considered the little italy of brooklyn. >> you spent hours and hours, basically on this street corner. >> yeah waiting for him to come home from work. >> reporter: at one point, she even dons a burka. >> a muslim friend hooked me up with this beautiful burka, and

said, "you can get up close to anyone you want and eavesdrop." >> i remember listening to a conversation. he was talking about blondes. he liked blondes. that's when i decided to go really blonde. >> reporter: five long months into the sting and she is ready to make her move. >> i rode my bike past him several times up and down the block waiting for him to notice me. then his friend whistled at me, and my heart dropped, and i said hi. and i said i was from california, and i was new to the neighborhood. and he said i could give him a call. >> reporter: desperate for anything she thinks will sink her new persona also rents a bachelorette pad. >> there was a futon for a bed, and a table, a couple of chairs, designed to be a so-called playgirl's pad. >> how long were you here? >> a year. maybe a year and a half.

>> reporter: armed with a brand-new life and a sexy cover, she is ready for her next brash move, a romanti romantic dinner, with juror number eight. >> you would've done whatever it took? >> yes. >> even if it meant taking him to bed? >> of course. of course. >> but it didn't come to that. >> no. no. we had a friendship. >> reporter: they drink wine, order take out, and listen to the rolling stones -- while doreen says, allo was rolling something else. >> and you're also smoking weed with him? >> i'm, like, am i going to feel paranoid, you know, am i going to blow my cover? >> how much of your conversations were audio recorded? >> all of it. >> reporter: yep, it turns out in addition to her push-up bra and daisy dukes doreen was wearing something else. a wire. >> and you kept it where? >> between my boobs. >> hello, hello? i'm nervous as hell. >> and so during this entire time you are this california girl? >> yes. >> i grew up in california. so, no offense, but you don't sound like you're from

california. >> one time he caught on and he said, "you sound like you're from brooklyn." and i said, "i'm taking classes. so they must be working." >> reporter: slowly doreen builds allo's trust -- turning their conversations toward her son john's murder trial. >> and you could have got excused. there's a million and one excuses to get excused. >> the number one excuse, i'm prejudiced. >> you're what? >> i hate jews. >> he believed that john was jewish. >> reporter: it's hardly enough to win a retrial, but then, doreen says, allo drops a bombshell. >> technically by law if i knew that, i shouldn't have even been in that jury. >> say that again -- >> i shouldn't have even been in that jury because -- >> why not? >> by law, you're not supposed to be. >> reporter: for doreen, it's a gotcha moment. she says, if what allo is saying is true he should never have been on the jury because he knew some of her son's friends.

>> i'll tell you this, but i'd never tell anybody else. i actually had some type of information. >> about? >> remember when i told you that they hang out over here sometimes? >> right. >> so when allo started confessing that maybe he didn't belong on this jury and that he had known some of the kids, what was your reaction as you're tape recording this? >> i was disgusted with him because he said it proudly and, he's bragging how he put this kid away. >> what did you want to do? >> i wanted to punch him in his face. >> reporter: doreen thinks she finally has the goods on juror eight, and believes it can win her son's freedom. but in so doing, she may have lost something else. >> what did the undercover sting do to your marriage? >> it destroyed it. >> you were quoted as saying, you know, "i can get another husband. i can't get another son." >> that's right. >> reporter: but can she get her son's murder conviction

overturned? still ahead -- >> i'm gonna show this video of -- allo. >> oh, god. >> reporter: that juror now in the hot seat. >> this is a bunch of mularkemu. >> reporter: you're going to want to hear this next.

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>> reporter: call her the "undercover mother." after 11 agonizing months of surveilling and seducing juror eight, jason allo, doreen quinn giuliano thinks she's sitting on gold. an admission she says allo made on a secret recording that he should never have been on the

jury that convicted her son. >> by law you're not supposed to be. they read you a list of all the witnesses if you know or are affiliated with these people in any way. you have to let them know. >> here's somebody admitting to you that he lied, which is contempt of court and perjury. >> an unbelievable story of a mother trying to get her son out of jail. she goes undercover, a double life -- >> reporter: october 2008 -- news of doreen's undercover exploits become public and the press is in a frenzy. >> this has to be put down on the record. >> reporter: abc news scores an interview with that juror, jason allo for "nightline." with his attorney by his side sometimes even in his lap, allo denies to martin bashir the things doreen claims she caught on tape. >> number one excuse, i'm prejudiced. >> you're what? >> i hate jews. >> do you ever recall saying anything like, "i hate jews." >> not at all. >> he would never say anything like that. >> can you tell me, jason? >> i'm not a prejudiced person. >> is it the sort of thing that

you imagine you might've said in the past? >> what does, what does that have to do with the, with the interview? >> i'm just asking him a question. >> but it doesn't make sense. >> well it does because i'm coming to a point. >> all right. go ahead. don't answer him. there's no reason to answer a question like that. >> you see, in, in one of the tape recordings you, you say, uh, you hate jews. >> that's, that's, that's your interpretation of the tape recordings. >> reporter: and what about that recording where allo seems to admit he never should have been on the jury at all? >> technically by law if i knew that i shouldn't have even been on that jury. >> can you ever remember saying, "i shouldn't have been in that jury"? >> he doesn't remember saying that, martin. >> no, do you, jason, ever remember -- >> no. i don't. >> did you commit perjury? >> absolutely not. >> were you lying to the judge when he asked if you knew anything about -- >> martin, this is ridiculous. this is the most ridiculous questions i've ever heard. these questions are nothing but tidbits. this is a bunch of malarkey! >> i wanted to get your reaction to this interview that we did. when you see his face what's your reaction? >> disgust.

>> he denied a lot of the stuff that you got him on tape saying. >> right. i have the proof. so now all's we gotta do is write a motion and submit it to the judge. >> reporter: and they did just that, filing a motion in 2008 to vacate her son's conviction on the grounds of juror misconduct. but after all those months the wine the wire the wooing, doreen's hopes are dashed. the judge shoots her motion down in flames -- casting doubt on the "reliability" of the recordings, and saying there was no evidence that allo intentionally lied. he even slams doreen personally denouncing her for "reckless" and "vigilante" behavior. >> he said that you were guilty of extraordinary misconduct. did you go too far? >> maybe it was misguided, but definitely not too far. because any mother would do it. >> you were painted as somebody who would stop at nothing to subvert the criminal justice system. >> as long as i follow the law, i don't see anything wrong with

it. >> reporter: so instead of giving up despite the resounding legal tweet -- defeat, in 2012, doreen decides to double down. >> so i decided to investigate each and every person who wrongfully testified against my son, and i started off with the jailhouse informant. >> reporter: that's right guica's one time prison mate turned informant john avitto the prosecution's star witness. remember, in damning testimony he claimed that giuca admitted to him that he pistol whipped mark fisher that night before his friend finished him off. >> this avitto was basically putting the target right on john giuca's head. >> reporter: doreen now sets her sights squarely on avitto to try to uncover why she believes he lied on the stand. this time she turns to a professional seasoned private investigator jay salpeter. >> i contacted john avitto and i asked to meet with him.

he was a little apprehensive. >> and how does a investigator like you move forward on uh, getting somebody to trust you? >> i like to start with, you get more with sugar than spice. >> reporter: the retired nypd detective coaxes avitto into meeting him in his white suv in this bensonhurst neighborhood. all the while his trusty tape recorder is rolling just in case the ex-con has something he wants to get off his chest. >> well, i was in riker's island, and me and john became good friends. >> reporter: but the jailhouse informant repeats his account that giuca was involved in fisher's killing. >> he did tell me he hit the guy on the head with the gun, the kid went down, he start kickin' and punchin'. he did tell me all that. >> he's sticking by his jailhouse confession. >> right, but i'm not ready to start a confrontation with him. just keep it going, let him speak, and as a detective, you learn when you let people speak, things come out. >> reporter: the wily pi has a hunch that avitto is suffering

from a crisis of conscience. he's able to lure avitto back into his suv two weeks later where the ex-con suddenly comes clean. that so-called jailhouse confession giuca made? never happened. avitto admits he fabricated the whole thing. >> i don't know, what else do you want me to say? >> i just want the truth, that's all. >> the whole thing was a lie. >> the whole thing was a lie? >> yeah. >> reporter: and there's another bombshell admission avitto claims that in exchange for his testimony the prosecutor and the detectives cut him a deal helping him stay out of jail -- even when he violated probation. >> i had gotten into violations of the program and stuff. and they helped me get out of those. >> right. >> just to keep me so i can testify. >> and you knew that you were supposed to put you in jail, right? >> right. >> reporter: in the years since giuca's conviction, that prosecutor anna-sigga nicolazzi did alright for herself even becoming one of those high profile legal eagles on tv. >> i've been prosecuting murders

for 15 years, i've never lost a homicide case. >> reporter: but the giuca case raises questions about that perfect record. was hers a win-at-all-costs mentality? did nicolazzi violate court rules by not telling giuca's defense team or the jury that she helped the informant stay out of jail? >> if it's true that she made promises to this critical witness to help him out in exchange for his testimony and didn't disclose it, that's a grave legal sin. >> you hit the jackpot. >> we hit something big. you have a recantation, you have prosecutorial misconduct, all wrapped up in one. >> reporter: coming up the tables have turned. now it's the star prosecutor who takes the stand to defend her handling of the giuca case. >> did john avitto lie during the trial? >> john's going to come home. >> reporter: will the "undercover mother" finally win freedom for her son? >> we're going to win. >> reporter: when "20/20" continues. amel is the strong, w,

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>> reporter: november, 2015. john giuca has now been in prison for more than a decade. in this interview with crimewatch daily, he maintains that he is innocent. >> i did not murder mark fisher. i had nothing to do with -- all i did was have a party that night. and now, i'm in prison for 25 to life for something i didn't do. >> here we go. >> get our butterflies. >> reporter: for his mom, doreen, the trips to visit her

son in jail have been a living hell. >> seeing him there is heart wrenching. i hate it, i hate it. and the worst part is leaving. and i try not to cry because you know, you don't want your son seeing you crying. >> reporter: but while giuca languishes behind bars -- >> my job is to fight for justice. >> reporter: the legal eagle who sent him there is flying high. >> did they find a gun? >> reporter: telegenic former brooklyn prosecutor, anna-sigga nicolazzi brandishing that undefeated record as host of two crime shows on investigation discovery. >> let me take you inside the fight for justice. >> she comes out and she says, "you know, i've never lost a case." >> oh, god. you know why? because she's a cheater. >> reporter: a cheater, doreen says, because she didn't disclose that apparent deal with the prison snitch who helped convict her son. but remember, that star witness has now done a 180. in this sworn affidavit, john avitto says he lied to prosecutors, in exchange for what he says was a deal to keep him out of jail. >> this deal was never disclosed

to the defense. it was never disclosed to the jury. nicolazzi's dealings with avitto reflect the worst in how a prosecutor can violate the rules. >> reporter: and then, more dominos start to fall as two more of nicolazzi's witnesses recant their testimony, including giuca's then-girlfriend lauren calciano. in this sworn affidavit, calciano said she lied on the stand after nicolazzi and police put "relentless" pressure on her, threatening to "make this hard" for her father who was in jail at the time. >> people would say to me, "don't you hate lauren?" how can you hate a 19-year-old girl who was pressured into lying? i blame the prosecutor and the detective. >> reporter: it's 2015 and the "grid kid killer" case is back in the news yet again. but this time, the spotlight is on the tv star prosecutor, who ironically would later get a

show called "true conviction." >> this is "true conviction." >> reporter: now there are questions about how true her conviction of giuca really was. >> i think it's safe to say that if we knew everything we know now, when she prosecuted this case, she probably wouldn't gotten the conviction. >> reporter: armed with new ammunition, giuca's lawyer mark bederow goes to war. after the d.a. rejects a petition alleging prosecutorial misconduct, bederow turns to the courts to try to get the conviction thrown out. in a remarkable role reversal, it's the prosecutor's turn to take questions on the witness stand. >> i believe in the case, i believe it was tried justly. >> reporter: nicolazzi says she made no promises to avitto, and forcefully defended her handling of the giuca case. >> did john avitto lie during the trial? >> are you pointing to anything specific or overall? >> about anything? >> i don't believe so.

>> but all eyes are on nicolazzi's former star witness, jailhouse informant, john avitto. as a hush falls over the courtroom, avitto apologizes to giuca for lying about that so-called jailhouse confession. >> i apologize, i'm deeply sorry. >> reporter: seems like it should be a slam dunk. but if you can believe it, despite that complete about face, the judge shuts giuca down. >> i have denied the defendant's motion to vacate the judgment. >> reporter: somewhere between diskraugt -- distraught and stunned, doreen and her p.i. salpeter, look on. as the judge concludes, there was no deal and that the jailhouse informant never benefitted for testifying. >> you have hope, it's taken away from you. and the crash is worse. just makes you wanna curl into bed and not get back out. >> reporter: but the battle's not over. attorney bedorow counter attacks by firing yet another legal salvo, appealing the judge's decision.

>> is there any way that you're blinded by your mother's love and you're not seeing something about what happened that night? >> look, it's the facts that drive me. not a feeling or a hunch, it's the facts. and i beg the judge, the public, just look at the facts. >> reporter: then, this february, in the waning days of a long, cold new york winter, an unexpected phone call from her son's lawyer. >> i thought something terrible happened. i thought we lost. and he said, "are you sitting down?" and i said, "yes." he said, "we won. we won." i screamed. i threw the phone. i thought it was a miracle. >> reporter: in a stunning decision, a panel of four appellate judges unanimously overturn her son's conviction. the judges conclude, that, in fact, nicolazzi committed a clear violation of court rules that she had helped avitto and

should have told the defense. doreen has seemingly won her 13-year long legal campaign. so why hasn't she finally been reunited with her son? >> don't you come home when you are presumed innocent? >> reporter: why is john giuca still in jail? i look like most people. but on the inside, i feel chronic, widespread pain. fibromyalgia may be invisible to others, but my pain is real. fibromyalgia is thought to be caused by overactive nerves. lyrica is believed to calm these nerves. i'm glad my doctor prescribed lyrica. for some, lyrica delivers effective relief for moderate to even severe fibromyalgia pain. and improves function. lyrica may cause serious allergic reactions,

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because unlimited is only as good as the network it's on. >> reporter: it might be springtime on stratford road in brooklyn, but for doreen quinn giuliano, it's been looking a lot like christmas. >> how long has this christmas tree been here? >> 13 years. >> so you never took it down? >> no. he was on his way home to decorate the tree, and he never made it home. >> and so you've kept this up? >> yes. >> waiting. >> waiting. >> reporter: and doreen is still waiting for her son to come home even despite that appellate panel's unanimous decision to throw out john giuca's murder conviction. why? because the brooklyn d.a. has decided to appeal that court's decision, and have asked another judge to deny bail, keeping him locked up, while they decide whether to retry him. >> i find no reason to release the defendant, nor to grant bail in this case. >> if four judges all agreed

that the trial was flawed wouldn't it be logical that you send the guy home? how much does the guy have to suffer? >> reporter: former prosecutor anna-sigga nicolazzi declined to speak with 2020. and, the current d.a. declined to talk with us as well. >> there's no question in my mind that john giuca was one of the individuals culpable in the death of mark fisher. >> reporter: but consider how much has changed in giuca's favor in the thirteen years since the first trial. today, the jailhouse informant and giuca's ex-girlfriend, both say they lied on the stand. and just this week, huge headlines. "20/20" has learned brooklyn defendants interviewed giuca's co-defendant, antonio russo who reportedly confessed to fisher's murder for the first time. he says he used his own gun. >> so, in a retrial, how strong a hand does the prosecution really have to play? >> i'm surprised that prosecutors are moving forward with this case. i don't see how they're going to

be able to prove it. >> at this point, you have been disappointed so many times. >> over and over again. >> is there part of you that is, like, cautious? >> of course, i'm cautious. but i'm optimistic too. >> reporter: meanwhile, her son remains holed up in rikers island jail. "20/20" cameras were rolling when john surprised doreen with a call. >> hi john, uh it's juju chang with abc new, "20/20." how are you? >> how you doing? >> did you have anything to do with the murder? >> absolutely not. i had nothing to do with the murder of mark fisher. >> what was your reaction when you found out the lengths your mother went to, to go undercover, to try to get to the truth? >> i thanked god, and i said to myself, "i'm so lucky to have her as a mother." >> i love you, john. >> all right. i love you. >> reporter: as her son's case continues to grind through the justice system doreen recognizes

there's another mom, and dad suffering too. >> some people might argue that the fishers deserve closure in this as well. >> and they do. of course, they do. >> and you had empathy for them. >> of course. of course. but in the same respect, i got to fight for my son's life, you know? i have to fight for my son. >> a mother who will never give up. and that's our program for tonight. thank you so much for watching. i'm elizabeth vargas. for david muir and all of us at abc news and "20/20," have a great night and a great weekend. rain and wind taking a toll in the east bay tonight.

>> giant tree