Nothing if not timely in its brief theatrical release this week at the Pioneer Theater, Irish filmmaker Shane O’Sullivan’s “RFK Must Die” revives visions of a brighter, bolder, better America 40 years gone — and yet much on the electorate’s mind. The film opens tomorrow, on the 40th anniversary of the assassination of Robert F. Kennedy, who was gunned down in the pantry of the Ambassador Hotel in Los Angeles with a whole nation watching. The senator from New York had just delivered a rousing speech after his triumph in California’s Democratic primary, signaling the likelihood that he would challenge Richard Nixon for the presidency that fall.

Contemporary jitters about another promising, liberal politico — the Democratic front-runner and presumptive nominee, Senator Obama — have been encouraged by recurrent public allusions to history repeating itself. Voices as diverse as rapper 50 Cent and Democratic contender Senator Clinton have suggested that Mr. Obama could be a moving target, the latter specifically evoking RFK’s assassination (and stumbling all over herself to apologize after making the impolitic analogy).

That alone is not enough to compel a strong interest in Mr. O’Sullivan’s exhausting exhumation of the case, but it’s a good hook. And it’s not the only one. The murder resulted in a life sentence for a meek Palestinian named Sirhan B. Sirhan, “America’s last surviving political assassin,” as the film’s publicity notes call him, and also our first glimpse of a Middle Eastern “terrorist.” If you are old enough to remember the occasion, are a fan of conspiracy-theory movies, or simply feel that Robert Kennedy never got equal time, given the never-ending speculation over the 1963 assassination of his older brother, then “RFK Must Die” is worth its weight in popcorn.

Mr. O’Sullivan, whose door-stopping book, “Who Killed Bobby? The Unsolved Murder of Robert F. Kennedy,” also arrives tomorrow, asserts that Sirhan was a patsy, just as Lee Harvey Oswald is alleged by some to have been five years earlier. This wasn’t a suicide mission by a militant outsider, the theory goes; it was an inside job. The filmmaker fingers a trio of CIA agents whose faces appear repeatedly, and mysteriously, all over footage captured before and after the fateful moment at the Ambassador. The documentary revives old doubts about the conclusions drawn by the Los Angeles Police Department, particularly those regarding the shots fired: New forensic evidence culled from an audiotape supports the case that 14 shots were fired, not the eight bullets in Sirhan’s gun. That, in turn, implies a second shooter, with Sirhan acting as a decoy.

The film goes about this business methodically, marshalling a parade of vintage government, law enforcement, and investigative types to comment on grainy footage that is analyzed for meaning like dried tea leaves. Some people obsess over this kind of exposé, though such obsessions become an end in themselves. Mr. O’Sullivan works to maintain a certain balance, though unschooled viewers may find their focus wavering. It’s hard to accept a lot of what is presented as anything more than hearsay.

The prime suspect, a formidable spook and coups d’état specialist named David Morales, would seem to be guilty as charged based on secondhand comments from his former associates, who report him once gloating after a few too many drinks: “I was in Dallas when we got the son of a bitch [JFK] and I was in Los Angeles when we got the little bastard.” Morales is long dead, so such conjecture seems to be just that. Though it’s all skillfully framed and outlined by Mr. O’Sullivan, producing an aura of inevitability, the film’s most appealing aspect may be its real-life “X-Files” vibe.

Especially amusing is the exploration of Sirhan as a brainwashed, “Manchurian Candidate”-style assassin who was under hypnosis when he began firing shots at Kennedy and, despite the efforts of expert shrinks, has never been able to recall his participation in the actual crime. And who was that woman in the polka-dot dress? Mr. O’Sullivan’s drive to find answers is admirable, as he plunges deep into the thicket of memories harbored by a gallery of gray-flannel former operatives in their dotage and an RFK volunteer staffer who took a fateful cigarette break. Whether or not he inspires enough curiosity to officially reopen the case, Mr. O’Sullivan knows how to spin a yarn, even if it’s one that many people will not want to hear.

Through June 12 (155 E. 3rd Street, between Avenues A and B, 212-591-0434).