Michael Jackson was one of the most photographed celebrities who ever lived. But in “Leaving Neverland,” a devastating four-hour, two-part documentary that portrays him as a serial predator, there are photographs of Jackson that have a quality unlike anything you’ve ever seen. They are homespun, casually candid, sitting-around-the-living-room shots, most of them snapped during the visits that Jackson paid to the modest boyhood homes of the two men the movie is about: Wade Robson and James Safechuck, both in their late 30s, each of whom describes, with disarming eloquence and self-possession, how Jackson befriended them when they were children and then, for years (starting when they were 7 and 11 years old, respectively), sexually abused them. The film suggests that they were far from the only victims.

In “Leaving Neverland,” the testimony of Robson and Safechuck is overwhelmingly powerful and convincing. And one reason it’s more powerful than anything we’ve previously encountered on the subject — though plenty has been reported about it, beginning with an in-depth Vanity Fair article in 1994 — is that the two don’t just describe the sexual activities they say Jackson subjected them to (oral sex, mutual masturbation, the viewing of porn). They describe, in abundantly articulate and deeply emotional detail, how abuse took place within the context of what appeared (to them) to be a relationship of hypnotic warmth and trust.

Jackson became the kids’ “pals,” and he befriended their families, too. The photos catch him sitting around with them, looking surprisingly not “on,” with a relaxed, letting-his-hair-down vibe we’re unused to seeing. Of course, he was still the biggest celebrity on the planet, a reality he used in the most manipulative way possible. The phrase that keeps coming up in the movie is “larger-than-life.” He truly was. And that’s part of what’s gripping and dismaying about “Leaving Neverland.” The filmmaker, Dan Reed, forces us to confront the idea that the greatest pop genius since the Beatles was, beneath his talent, a monster. “Leaving Neverland” is a kind of true-life horror movie. Some will walk out of it shaken, others, on some level, liberated by the extent of its claims.

Jackson, no surprise, met the two boys through show business. Wade Robson grew up in Brisbane, Australia, and during Jackson’s 1987 concerts there a dance contest was held for children, the winner of whom would get to meet Jackson. Robson, who was five at the time, was officially too young to enter the contest, but they let him perform anyway; he did the scissory moves from the “Bad” video wearing a pint-size buckled-black-leather outfit, and he was an instant hit. (As a kid, Robson already showed a hint of the talent that would lead him, as an adult, to make a name for himself as the choreographer for ‘N Sync and Britney Spears.) Meanwhile, James Safechuck, then 9 years old, starred in one of Jackson’s Pepsi commercials — he was the kid who pokes around Michael’s dressing room, then flashes a bedazzling smile when the star walks in on him. That moment in the commercial was, literally, the first time he’d ever seen Jackson in person.

Jackson invited both boys to perform with him on stage as one of a group of kiddie mascots, then visited Safechuck at his family’s home in Simi Valley, Ca. His relationship with each boy was separate, but he would ask each of them on what might be called play dates, and from there, Robson and Safechuck say, he’d spend time with them in his bedroom. For a while, the parents say they lurked close by, but after some gentle parental arm-twisting Jackson would get the kids to share his bed for the night. By the time he was inviting the families up to Neverland Ranch, the film claims that arrangement became the norm.

How could any sane parent have gone along with this? That’s an obvious question, and one’s initial response is to say: It’s enraging, and unforgivable, that the parents allowed any of this to happen. But without letting the parents off the hook, “Leaving Neverland” shows that they found themselves under the spell of Michael’s celebrity. They thought he was creating opportunities for their children that might otherwise be taken away. And once inside their homes, he seemed the soul of gentleness. So they pulled the wool over their own eyes and enabled him.

The film portrays what happened behind those closed bedroom doors as hideous and criminal. But Robson and Safechuck describe, with great intimacy, the way it happened, and their feelings about it as kids, and that’s part of the revelation of “Leaving Neverland.” These children felt close to Michael Jackson, and to use their own words they felt a kind of love for him; they wanted to do what it took to please him. The movie characterizes one of the towering evils of child sexual abuse: that the victims may not experience it, at the time, as “wrong.” They are children who’ve been raised to please adults — and Michael Jackson wasn’t just any adult. The movie asserts his deviousness in how he began to crowd out the boys’ parents, and to effectively replace them.

The sexual activities are described with unnerving candor, and one’s inevitable response is to recoil in horror at the predatory sickness they portray. The documentary suggests that Jackson was a serial pedophile who came on as a protector of children. At the center of the movie, though, is a fact that will remain (for some) controversial: that both Robson and Safechuck testified, during Jackson’s first criminal trial for child sexual abuse, that he was innocent — that he’d never done a thing to them that was inappropriate.

The movie explains, quite believably, how this happened. Jackson, during the years of alleged abuse (for Robson, it was from the ages of 7 to 14), would tell the two boys, repeatedly, that they couldn’t reveal any of what went on; if they did, Michael is claimed to have said, both he and the boys would go to jail for life. The film maintains that he struck a note of primal terror and diseased loyalty in them, so that they felt they couldn’t reveal what had happened. The two men say that they lied to their parents, to their future wives, and to the courtroom. But far from “poking a hole” in their story, “Leaving Neverland” says that this level of denial at all costs is, in fact, an intrinsic element of the horror of child sexual abuse. It always starts off as a terrible secret, and quite often remains so. The compulsion to cover it up — out of fear or shame, or both — is part of the insidious nature of it.

The second half of “Leaving Neverland” is mostly devoted to how Robson and Safechuck got in touch with their trauma and began to recover from it, something that only happened after Jackson’s death. It’s an essential part of the story, and part of why this is an important film. Yet there’s one element of “Leaving Neverland” that remains largely unexamined: what was going on in Michael Jackson himself. It leaves us to speculate as to what it was that made him the predator portrayed here. That said, it’s hard to escape the feeling that his untimely death, which resulted from his use of a sleep anaesthetic he was warned could kill him, may have grown out of the years he purportedly spent as an abuser. The way he died — so reckless, so unnecessary — counts as an unconscious act of self-destruction. It may be the expression of the guilt he couldn’t let himself feel.