LONDON — A suspected paramilitary serial murderer active during the Troubles in Northern Ireland has been named for the first time in a film by an Oscar-winning documentary-maker who alleges that the shooter was a former British soldier and his killing spree was covered up by the authorities.

Alex Gibney’s extraordinary new film about the unsolved 1994 Loughinisland massacre, which left six men dead as they watched a World Cup match, alleges that the perpetrators were known to police officers. Yet officials never brought charges against members of the gang—which included at least one informant who was working for the British government at the time.

The Catholic victims of the mass shooting were enjoying one of the greatest moments in Irish sporting history—a 1-0 World Cup win over Italy—when members of a Loyalist paramilitary group walked into a pub in the quiet village of Loughinisland and unleashed a hail of bullets toward their unguarded backs.

The man suspected of pulling the trigger was named simply as “Person A” in an official inquiry published last year. The report said he was also suspected of carrying out several other murders, including at least one while he was a serving member of a British Army regiment that was tasked with protecting Northern Irish civilians from terrorists like him.

Gibney names the likely suspect as Ronnie Hawthorn, who now runs a contract cleaning business with his wife and continues to live close to the village that was devastated by the massacre.

Clare Rogan, whose husband, Adrian, was shot in the back during the attack, was at the London Film Festival premiere of the documentary, No Stone Unturned. She told The Daily Beast that it was a great relief to finally have her husband’s alleged killer exposed. She said she is confident the film would offer renewed hope to the survivors and victims of other terrorist atrocities that have been left unsolved by authorities.

“It makes us feel so much better that it is out in the open, and it lets the other families know it can be done,” she said. “I don’t have any feelings about the gunman. It’s the coverup that makes me angry—the deceit, what they allowed to happen.”

The families initially put their faith in the police to solve the murder and did not speak out to demand justice until almost a decade after the cowardly shooting. The name of the documentary derives from Rogan’s memory of the police officers who promised to find out who had murdered the father of her children. In an interview in the movie, she says: “I’ll never forget their words: ‘We will leave no stone unturned.’ Those words never left me because I don’t think they ever lifted a stone.”

A solicitor acting for the families appeared on screen to say that from his very first consultation it was obvious something was very wrong with this investigation. The cops had ditched the getaway car, which had been sold to the killers by a police informant; there was no examination of the field where the vehicle was found; the DNA evidence was mishandled; the suspects were tipped off before they were arrested; their interviews were not properly conducted; and the notes from them were lost. One accomplice confessed to the crime in a letter to the police, and yet still no charges were ever issued.

The film even suggests that officials had been tipped off before the massacre took place.

Gibney (Enron: The Smartest Guys in the Room, Going Clear) met some of the families while making a short film on the World Cup massacre for ESPN. He was drawn deeper into their quest for justice, and three years later he is able to answer some of their questions.

“At least one of the members of the gang of four was working for the state [as an informant] at the time of the murder. That’s pretty shocking. That’s Whitey Bulger!” Gibney told The Daily Beast.

His reexamination of the case drew on decades of research by investigative journalist Barry McCaffrey, who Gibney described as “a hero.” He also interviewed several police officers involved—some of whom admitted that their investigations had been curtailed and directed from above.

“You have some good cops, you have bad cops, and then you have higher government pressure based on this idea that informers may have been involved,” said Gibney.

Did the British government in London decide that this murder of six unarmed Catholics was better left unsolved in order to protect a Protestant paramilitary informant and spare them the embarrassment of admitting that a British Army soldier was involved?

Gibney wrote to John Major, who was the British prime minister at the time, and other senior officials, as he tried to discover who had issued the orders to cover this crime up. None of those senior London officials were willing to take part.

As well as a deliberate coverup, Gibney cites the sometimes fraught relationship between different branches of security and law-enforcement agencies as possible reasons for the failure of the investigation.

“I’m working on a fiction project now, which is based on nonfiction material, which is all about that same tension between intelligence and criminal justice. It’s about the war between the FBI and the CIA in the run-up to 9/11—it turns out the CIA was hiding the ball. They knew 18 months prior to 9/11 that two noted terrorists were in country, two people who would ultimately be on the plane going to Washington, D.C. but they didn’t tell the FBI, and I think there are similar issues in the Loughinisland case,” he said.

“There’s a skill of picture-building and you become obsessed with that and you think that’s much more important than bringing particular criminals to justice. And over time—in some instances—that may be true. But sometimes someone from the outside needs to say: ‘Wait a minute here, there was a massacre, six people are dead. Don’t you think this would be one of those moments when people get brought to book?’”

It’s unclear how Northern Irish authorities will react to this movie, but there is no statute of limitations preventing Hawthorn and his alleged gang from being charged with the mass murder even now.

Emma, Adrian Rogan’s daughter, vividly remembers the day she was told: “Bad people came into the pub and Daddy was dead.” She was one of the strongest advocates for kicking up a fuss and demanding that her father’s murder be solved 23 years later. At one point during the film, she breaks down in tears and says: “All we wanted was for someone to tell us the truth.”