Max Spiers, 39, who is originally from Canterbury, travelled to Poland in July to give a talk on UFOs and government cover-ups but was found dead on a sofa in the flat he was staying in.
The father-of-two reportedly sent his mother, Vanessa Bates, 63, a text message two days before he died, which said: “Your boy”s in trouble. If anything happens to me, investigate.”
After waiting for the results of a post-mortem only to find that Polish authorities failed to perform one, Vanessa now believes her son was killed by Government agents.
She said: “Max was a very fit man who was in good health and yet he apparently just died suddenly on a sofa.
“He was making a name for himself in the world of conspiracy theorists.
“But I think Max had been digging in some dark places and I fear that somebody wanted him dead.”
She added: “[Polish authorities] are also refusing to release any paperwork about it to me because, absurdly, I don”t have his written permission.
“All I have is a death certificate from the Polish authorities that it was from natural causes.”
Vanessa arranged for Max”s body to be flown back to Britain where an autopsy was carried out, but two months later she is still waiting for the results.
She said: “Apparently, he had not suffered any obvious physical injuries. He could have been slowly poisoned – which is why the results of toxicology tests from his post-mortem are so important.”
Max”s online followers are also convinced he might have been killed for getting “too close to the truth”.
A blogger for the website Project Camelot wrote: “The entire circumstances are suspicious and I urge everyone to encourage the release of details about what really happened and call for an autopsy.”
Another, Craig Hewlett, added: “If it wasn”t true what he talks about then why would they kill him? Healthy people don”t just get sick and die, they get poisoned.”
A spokesman for the North East Kent coroner”s office said they were in “very early” stages of investigation.