It’s a line we’ve all heard before, and it’s almost always a lie. But this time it’s true. Alex Gibney’s documentary “No Stone Unturnedis actually The Movie They Didn’t Want You to See. Back in April, “No Stone Unturned” was supposed to have its world premiere at the Tribeca Film Festival, a venue that’s championed much of Gibney’s work in the past. But, due to what its producers said were “ongoing legal issues,” the movie was pulled from the festival. On September 30, in a sold-out hall at the New York Film Festival, the eye-opening and often jaw-dropping “No Stone Unturned” received an overdue world premiere.

Gibney wasn’t forthcoming about the precise reasons behind the earlier cancellation, saying just that “some people were uncomfortable about the truths” in the movie. However, he did not answer the question about who they might have been. But the movie makes clear why there might be people who would fight its release tooth and nail. That’s because 23 years after an unsolved multiple murder in Northern Ireland with political connections, Gibney’s movie points fingers not just at the people it argues carried out the killing, but the highly-placed figures who covered up for them.

The killing itself was as senseless as it was brutal. On the night of June 18, 1994, O’Toole’s Pub in Loughinisland, Northern Ireland was packed with punters enjoying watching Ireland trounce Italy in the World Cup match at New Jersey’s Giants Stadium. Then, a man wearing a black balaclava walked in and sprayed the room with an assault rifle before jumping into a getaway car and disappearing into the night. Six men were killed. Photos of the aftermath show a narrow space, just a humble small-town bar with the look of a basement rec room, with the floor is slathered in blood. Witnesses talked about the bodies of the dead and wounded lying in heaps.

It was assumed this was the latest violent eruption of the Troubles. O’Toole’s was known to be a Catholic bar, and just a couple of days before, three members of the Protestant paramilitary force, the Ulster Volunteer Force (UVF), had been gunned down not far from Loughinisland. But this wasn’t the 1970s anymore when the streets of Belfast looked like a colder, northern version of Beirut; Gibney knits together a quick montage of street-fighting footage from the bad old days scored to Sham 69’s pulverizing “Ulster.” The seas of jubilant green-wearing Irish at Giants Stadium symbolized an optimism that Northern Ireland could move past the old sectarian divide, as did the rumblings of a peace accord with the Catholic Irish Republican Army (IRA).

Condemnations of the murder came swift and forceful, as did promises of harsh justice from the Royal Ulster Constabulary (RUC), and several arrests followed. But not long after, the trail grew cold. In a country where the collusion between a terrorist paramilitary like the UVF and Protestant-aligned forces like the RUC and the British military had been an open secret, it didn’t take much for the lack of a resolution to the murders to seem like no accident. Suspicions would have been rife even if it hadn’t turned out, (as Gibney discovers during his tunneling about in the case) that the RUC, after coming across a treasure trove of leads, failed to do much with them. The getaway car was discovered, only to later be demolished. Forensics were half-hearted at best. Transcripts of interviews were destroyed. After the victims’ families had organized a public campaign for the case’s resolution, an internal probe was launched. It discovered “catastrophic” errors in the investigation.

So far, this is sadly par for the course with stories about botched law-enforcement work. Interviews with the victims’ family are a study in frustration, compounded by the litany of mistakes made and leads not followed. Not to mention the sickening waste of the six dead, about whom the still-traumatized bartender there that night says, “you couldn’t have hand-picked more innocent men to kill.” It’s an innately gripping story, but one that appears to be following a well-trod path from tragedy to open-ended questions awaiting resolution.

But Gibney’s curiosity, piqued by a short he had done on the case for ESPN’s “30 for 30” series back in 2014, leads him to dig further into not just what went wrong in the case, but why. The threads he pulls at quickly reveal not just collusion between government bodies sympathetic to criminal groups of a particular bent, but outright collaboration. Using that bloodhound instinct that has made his better movies such thrilling investigations, he stitches together documents and interviews into a narrative that shines some light into the case’s dark corners. By the time the movie is done, not only has Gibney crafted a plausible explanation for the RUC’s inability to solve the case, but also puts names to each of the balaclava-wearing men involved in the attack on O’Toole’s Pub. It’s an audacious work of journalism, the kind of potential cold-case resolution that true-crime documentarians dream about.

Even though he employs some of its standard tools in “No Stone Unturned,” such as the recreation of the murders that open the movie, true crime isn’t normally Gibney’s territory. The clichés necessary for that work aren’t really his preferred methods. In a field heavy with glitzier and more emotive filmmakers, Gibney is generally happy to let the work speak for itself, whether it’s the horrifying cyberwar scenarios envisioned in “Zero Days,” the Byzantine inner workings of a fearsome cult in “Going Clear: Scientology and the Prison of Belief,” or the gonzo greed of “Enron: The Smartest Guys in the Room.”

Like those wide-angle stories, “No Stone Unturned” goes past the true-crime spine of its narrative to explore broader issues, particularly the moral rot that comes with long-term internecine warfare and the corrupting influence of informers. One journalist tells Gibney that protecting informers no matter what crimes they’ve committed became so important to the authorities, that “the intelligence tail began to wag the dog.” In the case of Loughinisland, those kinds of decisions had a body count. [A-]

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