The word “tabloid” has a sleazy mystique. It’s such a potent word that it can influence the way you think about the subjects that fall into that category. “The Mystery of Marilyn Monroe: The Unheard Tapes” is a documentary that dives into what we think of as the most tawdry and sensational aspects of the Marilyn Monroe story: her death, on August 4, 1962, from an overdose of barbiturates; the hideous downward spiral of depression and narcotics that led up to it; and, buried deep in the weeds of all of that, the most scandalous piece of gossip ever connected to Marilyn Monroe – her clandestine affairs with John F. Kennedy and Robert F. Kennedy. This is dark, squalid, squinting-through-the-keyhole stuff, and it can make a film like “The Mystery of Marilyn Monroe” sound like a guilty-pleasure piece of true-crime trash, one of those glorified tabloid-TV exposés with a patina of investigative credibility. In fact, it’s a very good film. What’s more, there’s no reason, at this point, to go on pretending that what happened to Marilyn Monroe is some “sordid” pulp saga we have to peek at through our fingers from on high. In truth, every aspect of her life was connected to every other: her role as the greatest sex symbol of the 20th century; the melting radiance and magic she exuded onscreen, which were inseparable from her gifts as an actress; the desolate childhood that left her feeling, for most of her adult life, lonely and abused and abandoned; the parade of powerful and famous men she was involved with; and where all of that led – to a downfall that, in its tragedy, had as much meaning as her life did, which is one of the reasons its most explosive aspects were considered too dangerous for public consumption. “The Mystery of Marilyn Monroe” is the rare tabloid exposé that wants to set the record straight, and does. It confronts the key questions, as well as the conspiracy theories (was Marilyn murdered? If so, why?). And when you come out the other side of it, you may feel, for the first time, that you really do know what happened, and that it all adds up and makes a terrible kind of sense. The film was directed by Emma Cooper, who does a fine job of evoking Marilyn’s glory and her humanity; the archival clips she has assembled interweave Monroe’s unparalleled glamour with the way that, in private moments, she gave off a more soulful kind of luminescence. But Cooper is also working with the investigative journalist Anthony Summers, whose 1985 book “Goddess, the Secret Lives of Marilyn Monroe” is the basis of the documentary. Much of the news here, in other words, is far from new. But we hear clips of the interviews that Summers built his book upon – he spoke to a thousand people who were close to Marilyn or were in some way connected to her, with 650 of the interviews on tape. Listening to the recorded comments, we can judge the veracity of what we’re hearing. Cooper introduces a strikingly effective technique, having actors, talking on dial phones, lip-sync to the tapes, in clips that are shot with the grainy muted colors of old paperbacks. You could classify this enhancement as a dramatic distortion, yet it delivers the words we’re hearing with a heightening clarity that helps to dissolve the line between past and present. The effect of the technique is to transform the entire movie into a documentary noir, a ’40s/’50s plunge into the darkness. The film retraces all of Marilyn’s life, but does it through the lens of her relationships with men, building on the conventional-but-that-doesn’t-mean-it’s-untrue idea that her search for the stalwart father figure she never had led her into a self-destructive pattern of rejecting flawed saviors. Marilyn knew how to manipulate herself through the viper pit of Hollywood (the startling clip we see of her singing “Everybody Needs a Da Da Daddy” in the 1949 Columbia film “Ladies of the Chorus” has an almost confessional undertow). But once she’d achieved stardom, she fixated on becoming a good actress, which is why she started her own production company. Her failed marriages to Joe DiMaggio and Arthur Miller have, of course, been amply chronicled, with their elements of cruel fate (during the shooting of “Some Like It Hot,” she was pregnant with Miller’s child but miscarried). But in “The Mystery of Marilyn Monroe,” they’re viewed in hindsight almost as stepping stones toward her affairs with the Kennedys. Monroe’s relationship with JFK actually dates back to the early ’50s, when she’d just gotten famous and he was a dashing rich-kid senator, not very well known, who would hook up with her on his jaunts to California. (They drank at the Malibu Cottage, a divey place haunted by movie stars.) But in 1961 and 1962, after Kennedy became president, Monroe was carrying on simultaneous flings with both Kennedy brothers (she’d filed for divorce from Miller on Jan. 20, 1961, the day of JFK’s inauguration). She was playing with fire and so were they. You could say the essential mystery that haunts Monroe’s life is whether her death was accidental or a suicide. The way I’ve always seen it, her death, by pills, blurred the line between causality and passive despair; it’s eerily reminiscent of the death of Lily Bart at the end of Edith Wharton’s greatest novel, “The House of Mirth.” Yet the singular hidden mystery of Monroe’s life is the question of if – and how – her dangerous liaisons with Jack and Bobby were connected to her death. If there was a connection, that leads one to think that foul play was involved. In other words: Was she killed because she knew things that had to be hushed up? “The Mystery of Marilyn Monroe” presents compelling evidence, beginning with testimony by the family members of Monroe’s psychiatrist, Ralph Greenson (all of whom knew her), about how her relationship with the Kennedys spun her downward. It’s one of those early-’60s hornets’ nests of backroom politics, backroom sex, and cover-up. The Kennedys, due to Bobby’s doggedness as attorney general, had made an enemy of Jimmy Hoffa, the mobbed-up Teamster president. To get the Kennedys off his back, Hoffa was looking for dirt on them. So he hired the private detective Fred Otash (interviewed by Summers) to bug Peter Lawford’s Malibu estate, which the Kennedys used as their playboy retreat, and to bug Marilyn’s home as well. There were microphones under the carpets, in chandeliers, in the ceiling fixtures. Monroe was already being watched by the FBI because of left-wing associations she was known to have had, and when it emerged that she was having pillow talk with JFK about the bomb, she was classified as a threat to the presidency. We think we’re hearing the beginning of a conspiracy theory, and in a way we are. But Summers explicitly states that Monroe was not murdered. The result of her tangle of destiny was simply that the Kennedys, who had been tempting fate by carrying on simultaneous affairs with the world’s most coveted movie star, were told that they needed to cut ties with her; it had become too risky. And so they did. And it devastated her. Coming after a year of erratic behavior, where she’d barely gotten through the shoot of “The Misfits,” being dumped by the Kennedys sent her into a tailspin. JFK didn’t even say anything to her; she was ghosted. She died not long after. There is only one surviving photograph of Marilyn Monroe with JFK and RFK, the one with her leaning against a bookcase, bathed in shadow, taken at a party the night of the famous birthday rally for JFK at Madison Square Garden (the one where Marilyn serenaded him with “Happy Birthday, Mr. President”). And there’s a reason there’s only one photograph. Summers uncovers evidence of how the official scenario of the discovery of Monroe’s death – her housekeeper, thinking something was wrong, summoning Ralph Greenson, who found her body and phoned the police at around 3:00 a.m. – was a lie. It was a cover-up. Monroe had actually died, and been found, hours beforehand. What was being covered up, however, was not foul play. It was Monroe’s involvement with the Kennedys, which was at the center of the story. (The FBI was at her house that night, and Bobby Kennedy was in Los Angeles, until a chopper whisked him to San Francisco.) Yet that could never be allowed to come out, so it was excised from the story. It was suppressed by the government, the media, the mythology. “The Mystery of Marilyn Monroe: The Unheard Tapes” fills in the end of Marilyn’s life, and in doing so it lends her tragedy, in all its seeming sordidness, the dignity of emotional understanding. It also captures how, right up until the end, her story was bigger than she was, a story nearly as big as America.