Ending an interrogation in its investigation of the Boston Marathon bombing with a dead body and a host of new questions was not the sort of thing the FBI wanted.

But on May 22, an FBI agent shot Ibragim Todashev – a 27-year old former mixed-martial arts fighter and associate of one of the suspected bombers – seven times, killing him. The agent had just completed a lengthy interrogation of Todashev in his Orlando apartment, part of an inquiry into the already-dead bombing suspect, Tamerlan Tsarnaev. One of the bullets appears to have entered through the top of Todashev’s head.

The FBI’s story, doled out through anonymous leaks, changed several times in the weeks that followed. First, Todashev, who had voluntarily endured hours of questioning, lunged at the FBI agent with a knife, or even a sword. Then it was a length of pipe. Other accounts had him knocking over a table. At least one account held that Todashev was unarmed. The version that currently stands is that Todashev wielded a metal pole – or, perhaps, a broomstick.

Little is known about that mysterious pole-slash-broomstick: its heft, its dimensions, its use. Yet it is likely to be a major difference between vindication and damnation of the FBI’s handling of the case. A Florida prosecutor examining the case is expected to publish the results of an long-awaited investigation into Todashev’s death on Tuesday morning.

Unknowns accumulate in the Todashev shooting. Two Florida detectives reportedly aided the FBI interrogation, and their role during the shooting remains unclear. Florida’s autopsy report, available since July, was barred from release by the FBI. The bureau’s months of silence over the case have compounded the questions it faces.

But the FBI has already reached its conclusion. An internal FBI inquiry vindicated the agent, whose name is not public, months ago. That’s typical for the FBI – between 1993 and 2011, its agents fatally shot 70 people and wounded another 80, and the bureau found no major improprieties in any of those cases, according to records obtained by the New York Times last year.

Former agents say there are, generically, good reasons for many of those findings, such as training that outclasses that given to local police. But shootings like these are also split-second decisions that investigators may find difficult to second-guess – particularly when they identify with their fellow agents making those calls. And FBI investigators may also fear that finding against a colleague could come back to haunt them.

Mike German, a former FBI special agent now at New York University’s Brennan Center for Justice, said it was “critically important to have an independent investigation by state and local police as well as the FBI shooting investigation."

The Florida prosecutor conducting that independent investigation, Jeffrey Ashton, batted away reports on Friday that he has already exonerated the special agent who shot Todashev. He still may, and the bureau has to be hoping he will. The worst outcome for the bureau in the Todashev shooting would be for Ashton to contradict its findings and effectively indict its integrity.

Much as there is no stable picture of the Todashev shooting, there is no stable picture of Todashev himself.

Reportedly, just before he allegedly attacked the agent, Todashev was about to sign a confession implicating himself and Tamerlan Tsarnaev in a chilling September 2011 triple homicide in Waltham, Massachusetts. That homicide is itself one of the great counterfactuals of the case: an extensive Boston Magazine article this month suggests that more investigative work into the murders might have uncovered Tsarnaev before the Boston Marathon attack. Killing Todashev has rendered his and Tsarnaev’s involvement in the homicide an unresolved mystery.

Weeks before his death, Todashev – whom Boston Magazine described as possessing “a temper and proclivity toward violence” – was arrested after an altercation over a parking spot, but Todashev told police he didn’t throw the first punch.

Todashev’s family described him as the kind of fellow so harmless that he worked with disabled people. Following an October deportation of Todashev’s girlfriend, Tatiana Gruzdeva, family and supporters charged the bureau with mounting a campaign of intimidation. Todashev’s father has called the FBI “bandits” who killed his son “execution-style.”

Former FBI agents caution that most anything could be turned into a weapon by a man facing the prospect of extensive prison time.

“It’s not just the object that determines whether or not it is a ‘weapon’; it’s the intent of the person holding the object. In this case, the subject was a skilled martial artist armed with something that could have caused death or severe injury to the FBI agent or his colleagues,” said former FBI counter-terrorism agent Ali Soufan, who added that had Todashev not been shot, he might have gotten hold of the agent’s gun.

“It will be a fact question as to whether the agent reasonably feared for his life,” German added.

“Obviously, the FBI took his MMA training as a serious risk, and the analysis will be based on a totality of the circumstances. An object in another person's hands might not pose the same risk as it would in a trained fighter's hands.”

Revealing what Todashev held in his hands on the last night of his life won’t answer all the questions posed by his death. Nor will it tell the full story behind the Boston Marathon attacks, the last best chance for which now comes from the Dzhokhar Tsarnaev trial scheduled for November. But there’s no closure to a disturbing episode for the FBI without a thorough reckoning with what happened in that Orlando apartment.