A Russian supergrass who died in mysterious circumstances outside his Surrey home may have been poisoned in Paris before travelling to England, his associates have claimed.

Alexander Perepilichnyy, a wealthy businessman who sought refuge in Britain after supplying evidence against an alleged crime syndicate in Russia, collapsed while jogging outside his Weybridge home almost five months ago. Toxicology tests on the 44-year-old’s body have failed to reveal a cause of death, although murder squad detectives are investigating whether he was poisoned.

It has now emerged that British police have been working with their French counterparts after establishing that on the day he died, 10 November 2012, Perepilichnyy travelled by Eurostar to London after spending three days in Paris. During his stay, the Russian booked and paid for a room at the Four Seasons Hotel George V, off the Champs-Elysées, where suites can cost more than £4,500 a night, but he did not stay there. Instead, Perepilichnyy chose to stay at a more modest three-star, £145-a-night hotel across the city.

Associates of Perepilichnyy believe it is “highly possible” he met his alleged poisoners in Paris before catching a morning train back to London and from there to Weybridge, where he rented a mansion in the gated St George’s Hill estate. Just after 5pm, the apparently healthy Russian was found dead in the street.

In 2006 Russian exile Alexander Litvinenko was fatally poisoned after meeting two KGB officers who are accused of serving him a cup of tea laced with radioactive polonium at the four-star Millennium hotel in London’s Grosvenor Square.

A spokesperson for Surrey police said that no officers or forensics experts had travelled to Paris, but that they were receiving “advice and support from other agencies”.

Perepilichnyy’s life was considered at risk after he supplied documents to Swiss prosecutors implicating corrupt Russian state officials. His evidence tracked the proceeds of a £144m tax fraud against London-based Hermitage Capital that was uncovered by lawyer Sergei Magnitsky who, after notifying the Russian authorities of the crime, was arrested, tortured and died in police custody.

The latest developments follow the death of Russian oligarch Boris Berezovsky, whose body was found last Saturday on the bathroom floor of his Surrey mansion with a ligature around his neck. Police say there are no signs that any other person was involved in the death of the 67-year-old, but refused to rule anything out.

A growing number of people, including Berezovsky’s girlfriend, 23-year-old Annika Ancverina, are expressing doubts that the Kremlin critic took his own life. The results of toxicology and histology tests are not expected for several weeks. Surrey police sources expect the results of fresh tests on Perepilichnyy to be complete within the same time frame, although the failure to find a substance that might explain his death is said to have exasperated officers.

The absence of an explanation has raised fresh questions over the delayed reaction of Surrey police to Perepilichnyy’s death, in particular the fact that toxicology tests were not commissioned until three weeks later. “The toxicology reports, as I understand, are not showing anything positive. There is a possibility that they may come up with sudden death syndrome, which is very rare, but that would derive from a process of deduction,” said one source with knowledge of the investigation.

Dominic Raab, the Conservative MP for Esher and Walton, said: “The time lapse in commissioning the toxicology reports may mean we never definitively establish the cause of death. But there is a groundswell of suspicion deriving from Perepilichnyy’s good health, coupled with concerns he may have been at risk for giving evidence against Russian suspects in a Swiss money-laundering case.”

Dr Graham Mould, a consultant pharmaceutical toxicologist, said the delay could have made deciphering the cause of death more problematic. “After death, drugs sort of redistribute throughout the body. Stuff in the gut might then leach into the blood and so on. For example, you get fermentation of the blood that might generate alcohol when a person hadn’t taken alcohol. It would be very difficult to find out whether he did die of a particular poison.”

Former KGB agents have described how Russian spies are adept at using sodium fluoride, an odourless substance that can be lethal in certain doses and, as Mould points out, is complicated by the fact that fluoride is found in drinking water. Russian agents have also been known to administer poisons that can induce heart attacks but do not show up in postmortem examinations.

Toxicologist Dr Paul Illing said: “It falls in the same category as looking for doped athletes – it’s much easier if you know what you are looking for. If you are having to do a general screen, then there is always a problem of detection because you are trying to identify anything that is unusual; you can’t be as sensitive as possible to one specific substance.”

*Original article online at https://www.theguardian.com/uk/2013/mar/31/poison-claim-death-russian-supergrass