JFK files: Conspiracy theorists’ guide to what Donald Trump’s release will say about the assassination

Donald Trump might be about to expose one of the longest and most potent conspiracy theories in American history.

His decision to release the "JFK Files" – classified documents about the president's assassination – is sparking excitement among conspiracy theorists who hope that they might prove the truth, or otherwise, of what happened in Dealey Plaza on November 22, 1963.

Ultimately, it's unlikely that the documents will prove some of the more bizarre conspiracy theorists wrong, providing proof that Lee Harvey Oswald didn't kill JFK, or that he did it with someone else's help. But it could show something potentially more damaging about the US government and establishment: that it knew that such a killing might be about to happen, and either by malevolence or incompetence failed to act.

There is a mystery at the heart of JFK's killing, into which a number of different and non-official explanations have rushed to fill the gap.

Some claim that Lee Harvey Oswald couldn't possibly have acted alone, and so was enabled either by the Russians, the US government, friends or someone else entirely. The murder of Oswald just two days after he shot JFK leads to further questions: was it carried out by Jack Ruby on the request of one of the murky organisations that ordered the assassination of the president?

All of those theories, like all conspiracy theories, have their roots in the strange and momentous events of that day – they are the consequences of people poring through videos to find information that suits their idea that the killing can't have been a preventable and mundane act. But those observations and evidence are also mostly wrong, and there has been nothing dependable to suggest that the official account of that day isn't correct.

The ultimate fact is also that any conspiracy of that kind probably wouldn't be documented in the papers that are now held by the US government. There almost certainly wasn't another shooter – but even if there were, it's unlikely that someone in the US government would have written down that fact, or even known about it.

The conspiracy that the JFK files do shed light on could be far more damaging to the US government and the security establishment that continues to exist. And that might be exactly why Donald Trump has chosen to make them public.

“Of all the presidents since 1963, this is the one who would mind the least if the release of these documents damaged the CIA and the FBI, two organizations that he’s very angry at at the moment,” said Michael Beschloss, a presidential historian.

Because the real conspiracy and scandal that the JFK files show could finally illustrate why Lee Harvey Oswald – a man known to authorities, known to be a threat, and maybe even known to be preparing to kill the president – wasn't stopped before he did so. If that happened, it is a conspiracy not born of mysterious and arcane powers, but probably more the result of laziness and incompetence, and the desire to avoid being implicated in a world-shattering day.

It remains the case that the FBI, CIA and other bodies should have known about the killing. The files will hopefully shed light on the questions that inevitably follow from that moment: if they knew, why didn't they do something, and what did they do to cover up the fact they knew?

It's that conspiracy that's likely to be detailed in the JFK files, if any is. And it could be one that casts its shadows across the rest of US history and the conspiracy theories that animate it, because it doesn't simply suggest that something happened on that fateful day, but also that the same thing could be happening over and over again.