Actress and model Marilyn Monroe was found dead in her Los Angeles home on August 5, 1962, from an overdose.
But when a suicide note was never discovered and discrepancies in her case arose, conspiracies began to whirl that the movie icon was actually murdered.
Ahead of what would have been the singer’s 83rd birthday on June 1, the explosive claims have since re-emerged.
In 2017 documentary Unacknowledged, Dr Steven Greer claimed to have been given a top-secret wiretap summary of a phone conversation between Marilyn and former Attorney General Robert Kennedy, dated just two days before her death.
The pair were allegedly involved in an affair and government officials wanted to tap her phone to make sure she would not divulge any secrets.
The document – which Greer described as a “death warrant” – was titled “project moon dust”, a phrase that the conspiracist claimed was used by the CIA to talk about UFO projects.
In 2017 documentary Unacknowledged, he explained how “it mentions the visit by the President [with Marilyn] at a secret airbase for the purpose of inspecting things from outer space”.
“I don’t think they’re talking about meteorites,” he added.
Greer believed the reference to outer space and the visit with JFK was in reference to the New Mexico crash of the 1940s.
Official reports state the infamous incident was caused by a US Air Force balloon crashing at a ranch near Roswell, New Mexico in 1947.
But conspiracy theorists have long-thought the official line was a cover-up – and that it was, in fact, an alien spacecraft that crashed.
Greer claims he was handed the top-secret memo by a man whose family helped to start the National Security Agency.
He said he even had it verified by a high-level unnamed government official.
At the end of the clip, the professor says: “It was a tragic situation because she was an actress who didn’t understand the national security state and the viciousness of those who want to keep these sort of secrets.”
On his website, he added that “she was murdered” for the discovery.
Dr Greer is well respected among some UFO circles, but has been branded a hoaxer by more sceptical investigators, something he vehemently denies.
Jonathan Liu, CIA spokesman, rubbished claims of the confidential memo.
He said: “Such claims are baseless and do not merit serious consideration.”
It comes after a documentary claimed pieces of evidence taken by a coroner were destroyed.