During Columbus Day weekend in 2003, John Giuca had an impromptu party on the night of Oct. 11.
Mark Fisher, 19, was a sophomore at Fairfield University in Connecticut, where he was on the dean’s list and studying to become an accountant.
That weekend, he was hopping from bar to bar on Manhattan’s Upper East Side, when he ran into a girl he knew from school, and was immediately attracted to one of her friends.
Fisher and the woman later met up with another group that included Giuca.
After some members of the group were unable to get into bars because they were underage, Giuca, then 20 years old, invited everyone to his parents’ house in Brooklyn, New York.
According to witnesses, Fisher was intoxicated, didn't have a lot of money on him and had no way to get back to New Jersey, where he had been staying at a friend’s house that weekend, according to witnesses.
Watch the full story on "20/20" Friday, May 17, at 9 p.m. ET on ABC, including a new jailhouse interview with John Giuca.
Antonio Russo, aka "Tweed," is said to have supplied the marijuana at the party that night, according to authorities.
Police investigate the killing of Mark Fisher
What happened in the early morning hours as the party broke up is unclear, but somehow, Fisher’s body ended up on Argyle Road, two blocks from Giuca’s home. He had been viciously beaten and shot five times.
"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," retired New York Police Department homicide squad Lt. Robert Casazza told "20/20."
Giuca, who was in college studying criminal law and wanted to become a police detective, became a prime suspect in the murder.
Russo, then 17, was also under investigation, especially after some suspicious behavior.
"He [Russo] had dreadlocks that he had cultivated for years, so for him to get them sheared was very suspect," former New York Police Department detective and author Robert Mladinich told "20/20." "And then he takes off for California a couple of days later. That certainly makes him the prime suspect."
Police said everyone at the party was a person of interest, but with no hard evidence, the case was difficult to solve.
John Giuca goes on trial for murder
The murder remained a mystery after most of the people at Giuca's party retained lawyers and weren’t forthcoming to investigators. The investigation stalled for months.
Prosecutor Anna-Sigga Nicolazzi was assigned to the case and forced witnesses -- including Giuca’s friends -- to testify before a grand jury.
Eventually, the wall of silence cracked as some of Giuca's friends began to turn against him. Giuca and Russo were eventually arrested and charged with murder. Others who had been questioned, including Albert Cleary, were cleared of suspicion.
At Giuca's trial, which began on Sept. 12, 2005, the prosecutor argued that Giuca was a neighborhood thug and head of the so-called "Ghetto Mafia," out to get street cred by having Fisher killed.
Lauren Calciano, Giuca's on-again, off-again girlfriend, and Cleary were both witnesses for the prosecution, implicating Giuca in the killing.
John Avitto, who said he'd met Giuca while both were incarcerated at Rikers Island, also testified at the trial. On the stand, Avitto said that Giuca had told him that he had pistol-whipped Fisher before someone else then took the gun and shot him dead.
It took a jury two days to convict Russo. For Giuca, it was just a couple of hours. Both were found guilty of murder by a jury in Brooklyn, New York, and sentenced to 25 years to life in prison.
A mother’s outrage
Irate over the verdict, Giuca's mother, Doreen Quinn Giuliano, immediately focused on the jurors who had quickly convicted her son.
She went undercover to find out as much as she could about one juror in particular: Jason Allo, juror number 8, whom she learned had known some of her son's friends. For months, Giuliano staked out Allo's every move on a corner in Bensonhurst, Brooklyn.
Five months into her sting, Giuliano finally got his attention. She bought a burner phone and a fake business card. She went by the fake name "Dee Madison Quinn" and rented a bachelorette pad for more than a year.
She wore a recording device and recorded many of their conversations. Slowly, Giuliano gained Allo's trust, turning their conversations toward her son's murder trial.
"You could have got excused. There's a million and one reasons to get excused," Giuliano is heard saying in the recording.
In the recordings, Allo is heard saying that he's prejudiced and also revealing that he didn't disclose that he knew some of Giuca's friends during jury selection.
Giuca's lawyer submitted a motion alleging juror misconduct to the judge, citing the recordings Giuliano made undercover with Allo.
The judge denied the motion, however, ruling that the recordings were unreliable and that there was no evidence Allo had intentionally lied during jury selection. He also denounced Giuliano for her "reckless" and "vigilante" behavior.
In a 2009 interview with ABC News, Allo said he had told the truth in court, and he and his attorney Salvatore Strazzullo denied what Giuliano claimed she had caught on tape.
Mom continues crusade for her son's innocence
Allo insisted that he did not commit perjury or withhold information during jury selection.
After Giuca’s motion was denied, Giuliano and her son’s attorneys turned to private investigator Jay Salpeter, asking him to investigate Avitto, the jailhouse informant.
At Salpeter's first meetings with Avitto, he stuck to the story that Giuca had been involved in Fisher's killing. But in a later conversation, Avitto said he'd completely fabricated his account of Giuca’s involvement in the murder.
"The whole thing was a lie," Avitto is heard saying on a recording made by Salpeter during their conversation.
Avitto said that in exchange for his testimony, prosecutor Nicolazzi and detectives had helped him stay out of jail when he violated his probation.
"I [had] gotten into violations of the program and stuff. And, they helped me get out of those," Avitto is heard saying in the recording. "Just to keep me so I can testify."
Avitto followed up his conversation with Salpeter with an affidavit filed with the court in which he acknowledged he had "testified falsely" at Giuca's trial.
Two more witnesses for the prosecution -- including girlfriend Calciano -- also recanted their testimony. In a sworn affidavit obtained by ABC News, Calciano said she'd 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.
Pace Law School professor Bennett Gershman was retained by Giuca's family to help file a petition with the Brooklyn district attorney seeking review of Giuca's conviction and alleging prosecutorial misconduct.
"All I can say is that in any dealings that I had or the detectives had, I think we always found [Nicolazzi] to be of the utmost integrity," said Casazza, retired New York Police Department homicide squad lieutenant.
Where Giuca's case is today
The District Attorney's Office said it found no evidence of prosecutorial misconduct and Giuca's petition was denied.
Giuca's legal team then filed a motion in court to vacate his conviction based on prosecutorial misconduct. On the witness stand at a hearing, Nicolazzi denied she'd done anything wrong in the case.
Avitto also took the stand, recanting his testimony and apologizing to Giuca. Still the judge denied Giuca's motion. Giuca filed an appeal to get the judge's decision overturned.
In February 2018, after a 13-year-long crusade by Giuliano, Giuca's conviction was thrown out by an appellate court. The four judges said in their opinion that the prosecutor had erred by not telling the defense that she and police had helped jailhouse informant Avitto, which might have affected the jury's verdict. The judges added that a new trial was necessary.
On March 22, 2018, New York police detectives sent by the Brooklyn district attorney interviewed Russo, Giuca's co-defendant who had also been found guilty in the murder and imprisoned. He allegedly confessed that, using his own gun, he had shot and killed Fisher. In a police report of that interview obtained by ABC News, he did not implicate Giuca but did not clear him either.
Regardless, prosecutors contested the appellate court’s decision. On April 30, 2019, they argued before a panel of seven judges on the New York Court of Appeals, the highest court in the state, to have Giuca’s conviction reinstated. Giuca’s attorney, Mark Bederow, countered that the lower court had decided to throw out his client’s conviction, and that his client is entitled to a new trial.
A decision from the New York Court of Appeals is still pending.
If this court decides to reinstate Giuca’s conviction, he will be back in prison to serve out the rest of his sentence. But if it decides Giuca is entitled to a new trial, it will be up to prosecutors to decide if they want to go through with it.
In the meantime, even though his conviction was overturned, John Giuca remains in jail on Rikers Island. Even though his conviction was overturned, a judge denied him bail while the appeal process continues.