The mother of a conspiracy theorist who died in unexplained circumstances in Poland after telling her that he felt unsafe has said she hopes his inquest can fill in some of the “massive gaps” around his death.

Max Spiers had travelled to Poland to attend a conference when he died suddenly at the Warsaw home of a friend and fellow conspiracist, having previously fallen ill with a high temperature and then vomited two litres of black liquid, a pre-inquest review has previously heard.

Days before he died on 16 July 2016, he had messaged his mother, Vanessa Bates, in Canterbury, saying: “Your boy’s in trouble. If anything happens to me, investigate.”

But because Polish police were not informed about the death before his body was returned to the UK, it was not examined until more than a week after he died, when doctors in Kent were unable to determine the cause of death.

Speaking to the Guardian before his inquest, which resumes on Monday, Bates said: “I want answers. There are certain bits [of the story of his death] that are easy to follow, and other key areas that have massive gaps.”

When her son’s laptop and phone were later returned by the friend, a publisher called Monika Duval, Bates said, his computer had been wiped and the sim card was missing from his phone, though she was later sent the sim.

Spiers, 39, made his living by writing and speaking about paranormal and political conspiracy theories, and has become a cause célèbre among fellow conspiracists since his death, with intense online speculation over its unexplained circumstances.

At the time of his death, according to Bates, he was researching an organisation that he believed was involved in running a paedophile ring.

Shortly before his death, she said, “He had spoken to me, and he also sent me a message through WhatsApp saying: ‘Mum, I don’t feel safe.’ He even used the words: ‘I think I could be murdered.’ And I said: ‘What are you talking about?’ And then he was not clear. Then he was… ‘Just know that if anything happens, investigate it.’”

She said her son, who had two children, was “very, very charming”, but that he had also suffered from depression as well as being a reformed heroin addict. “In the three years before he went to Poland he was just fine … he was completely clean. But again, I don’t know what happened in Poland.”

A Polish lawyer appointed by Bates has taken statements from witnesses in Poland, including Duval, and members of the emergency services. But she said she did not expect them to attend the inquest, despite repeated invitations.

“You get some questions answered and more questions thrown up – there are a lot of contradictions, direct conflicts.”

She said she wasn’t sure what she hoped for from the inquest, “except that I want there to be enough for somebody to say, yes, there’s more to be looked at here. Because I believe there is.”

A spokesman for Kent police said that while the force was assisting the coroner it was not conducting an investigation into Spiers’s death, and referred further queries to the Polish authorities.

The inquest, at the Guildhall in Sandwich, Kent, is expected to last four days.