Max Spiers, 39, claimed to have shocking knowledge of UFO sightings and government cover-ups before his death.

He was found dead on a sofa while staying at Monika Duval’s home during a trip to Poland.

Now cops want to speak to the science fiction writer who was present at the time of his death and called the ambulance.

Warsaw prosecutor Lukasz Lapczynski said the nature of the relationship between Mr Spiers and Ms Duval remains unclear.

He told the BBC: “The nature of this relationship will be determined during the investigation.

“The doctor started resuscitation which was not successful. As a result of the doctor’s decision, the police weren’t involved in conducting additional procedures.”

The prosecutor said he plans to interview everyone who was present when Mr Spiers died.

His girlfriend Sarah Adams, 31, believed he was being held against his will and was bombarded with death threats days before he died.

Mr Lapczynski continued: “The information about Max Spiers’ death reached the prosecution office on August 30 when the body had already been transported to the UK.

“We couldn’t do a post-mortem which is essential in such cases.”

An inquest into Mr Spiers’ death was opened in Kent in December and is set to continue later this year.