At 10.05am last Monday, Martin Conmey entered the Hugh Kennedy courtroom in the Four Courts. He sat down next to his friend Dick Donnelly. Nearly 40 years ago, the two men sat beside each other in another courtroom, a few yards away in the Round Hall. On that occasion they were both on trial for murdering a neighbour, 19-year-old Una Lynskey. Both were convicted of manslaughter. Donnelly's conviction was overturned on appeal. Conmey served three years in prison and another 35 with the stain of being a convicted killer.

By 10.10am on Monday, his sentence had come to an end. Judge Adrian Hardiman, presiding over the Court of Criminal Appeal, declared the 1972 conviction quashed. There were gasps of disbelief and clapping broke out as supporters rose to their feet. Conmey looked dazed, like a man thrust into a strange, new world.

"Even when he [Hardiman] said the words, I didn't know that the conviction was quashed. I turned to Stephen [Cooney, his solicitor]. I was in shock. I couldn't believe it. I didn't let myself believe it. Then I just began crying."

He wasn't alone. His siblings and in-laws broke down. Supporters, like the four Kerrigan sisters, were equally overcome. Their brother Martin had been a friend of Conmey and Donnelly and was brutally killed in revenge for Una Lynskey's death after the three men came under suspicion.

At the back of the courtroom another two women observed in silence. Una Lynskey's sisters have never given any indication that they accept the innocence of the three men. The overwhelming evidence, however, suggests that a terrible miscarriage of justice was perpetrated against Conmey, and that his friend was killed over a crime he did not commit.

"It made me bitter, it destroyed me in some ways, having taken away so many years of my life, but at least the result restored some of my faith in the justice system," Conmey said last week.

"I'm just sorry my father didn't live to see my name cleared. And Billy Flynn, the private investigator who passed away recently. He worked tirelessly on the case. It's terribly unfortunate that Marty Kerrigan never had the opportunity to walk into a court to clear his name."

Lynskey disappeared after alighting from a bus at 6.55pm on 12 October 1971 near her home in Porterstown Lane, Fairyhouse, Co Meath. There had been sightings of a stranger in a car in the lane around the same time. Nothing came of it.

Without a direct lead to the mystery car, the garda investigation turned to a local man, 23-year-old Donnelly, who owned a car similar to the one seen. He, along with 19-year-old Kerrigan and 20-year-old Conmey, were brought into Trim station for questioning.

They were interrogated by members of the investigation section of the technical bureau. This was the section associated with a group that came to be known as the heavy gang. Later in the 1970s, and into the '80s, numerous allegations of ill-treatment were made against officers associated with the unit, including John Courtney, who questioned the three men in 1971. No charges relating to ill-treatment were ever brought against Courtney.

Assault

The three alleged they were abused in custody, but the gardaí have always denied this. There was some evidence that the men had been assaulted. There was damage to Conmey's hair, consistent with it being pulled viciously. The gardaí claimed that he began pulling out his own hair when he decided to come clean. This scenario of self-infliction of injuries was a theme that would be repeated many times in controversial cases over the following decades.

Conmey and Kerrigan signed statements of admission to encountering Una Lynskey on the night in question. They have always maintained that they signed the confessions following assault, intimidation and the promise that they could go home if they signed.

"I know people might say how could you make a statement about something you had nothing to do with," Conmey said. "But the mental and physical state I was in was indescribable. I was only 20 at the time. I would said anything they wanted me to say just to get out of there."

The thrust of his version of how he came to make an admission in custody would be repeated over the following 15 years by a completely disparate group of people, from Republican sympathisers to the Hayes family in the Kerry babies case. In every instance, the gardaí involved denied vehemently that anybody was ill-treated in custody.

On 10 December, Una's body was found in the Wicklow mountains. Nine days later, Kerrigan was kidnapped by two of Una's brothers and a cousin. He was brought to near the spot where Una's body had been found and killed. Pathological evidence suggests there was an attempt to castrate him within 10 minutes of his death. The three claimed Kerrigan was still alive when they left him. They were convicted of manslaughter.

The trial of Conmey and Donnelly took place a few months after the Lynskeys and their cousin John Gaughan were convicted. Crucial to the case against them were sightings of Donnelly's car in the lane that evening. Three witnesses, all young, local men, gave statements to that effect. What didn't emerge in the trial was that all three had first given statements saying they hadn't seen Donnelly's car. After they were brought to the garda station and interviewed by members of the investigation section, they changed their statements to say they had seen the car.

The only survivor from the three, Sean Reilly, told the appeal hearing earlier this year that he had been punched and abused by the gardaí and made to feel like a suspect. He signed the statement putting Donnelly's car in the frame. His friend Martin Madden signed a similar statement. The failure to produce the earlier statements at the trial was crucial, according to the appeal court, as the alleged sightings were a central plank of the prosecution case.

Commenting on Reilly's allegations that he was ill-treated in custody, Hardiman noted: "This explanation of why he made the second statement exists, and is, of course, heavily favourable to the defence and there is no other explanation before the court as to how that dramatic change came about."

The earlier statements never made it to the trial, and Conmey was convicted. He was sentenced to three years for a crime he didn't commit and was sent to Mountjoy. It was a hellish experience for a teenager who had never been inside a garda station previous to the case, never mind a prison.

"My mother used to come in on a Tuesday," he remembers. "She would be smiling and all, trying to give me a lift. At the end of the visit she'd be going out the door, I'd wave goodbye and she'd turn and I could see the tears in her eyes. I used to feel desperate going back in."

He served his sentence and returned to the close-knit community in the Porterstown Lane area. The Lynskeys had been part of that community, but soon after Una's brothers were released from their sentence, the family exhumed Una's body and moved to Kildare.

Martin tried to settle back into life, but the past and the pain was never far away. He met his future wife Anne in 1980, and, as with all new acquaintances, he had to explain his status. They married and in 1989, Anne gave birth to their son Raymond. A few months later, Martin was watching the news when an item on the release of the Guildford Four came on.

Innocence

"Gerry Conlon came out and raised his fist and said,' I'm an innocent man'. I had tears in my eyes when I saw that. I was an innocent man. Ray was only six months old. I said I had to do something for his sake if not my own. By then, we thought we had done everything possible. People said they knew I was innocent and I should just try to get on with my life, but I couldn't."

He went to local TD John Bruton, who raised the matter in the Dáil. The answer was that nothing could be done. The case had been through the system. Then in 1993, a new law, the Criminal Procedures Act, provided for cases to be revisited if new evidence came to light.

Conmey went to Patrick Tallen solicitors in Ashbourne and the company agreed to take on his case. Seeking the cooperation of the state was another matter. Not for the first time, a victim seeking redress from the state found the road back to court littered with roadblocks.

Initially, Conmey was told that the state was compiling all the documents and would forward them. Then in January 1998, the line changed. The state was "constrained by law not to release the documentation sought".

By the time a discovery order was finally served on the state in 2004, it emerged that a lot of the documents were lost.

According to Hardiman's judgement: "It transpired that this material was forwarded to Drogheda garda station in November 1997, some months after the defence solicitors asked for it. Directions were given that the material be secured. But it was in fact stored in the womens' toilets in Drogheda Garda station in a plastic refuse sack. Superintendent Walshe [the officer dealing with the case] speculates that perhaps between November 1997 and March 2001 the materials may have been mistaken for rubbish and disposed of. The room it was stored in was, it seems, rat- infested."

Despite the less-than-enthusiastic attitude of the state to a potentially wronged citizen, the truth was eventually uncovered. Apart from his solicitor, Conmey's sister Mary, Billy Flynn and Flynn's associate Tom Coffey, managed between them to piece together the missing parts, including the vital earlier statements of the three witnesses.

Finally, a mislaid file was located in the national archive in October last year. Martin Conmey was going to have his day in court.

"There wasn't a morning I woke up that it wasn't at me," Conmey says. "If it wasn't for the support of my wife Anne I wouldn't have been able to keep going."

Since Monday, he has tried to adapt to his new circumstances. There has been no euphoric rush, but wounds endured for 40 years will require time to heal.

Most of the families are still living in the Porterstown Lane area. Dick Donnelly married Martin Kerrigan's sister, Anne. Conmey's sister Mary married Una Lynskey's first cousin, Pádraig Gaughan.

Back in 1971, some of them were teenagers, some children, others negotiating the early straits of adulthood. The violent deaths of two of their number in that few months was to dominate the rest of their lives, at least until last week. For Martin Conmey and his loved ones and friends, some resolution has finally been arrived at. The Lynskeys have no such comfort. What fate befell their sister that October night remains a mystery.