British counter-terror police have launched a murder investigation into the death of Russian Nikolai Glushkov in London.
The Metropolitan Police said a post-mortem examination found the cause of the 68-year-old's death was compression to the neck.
Mr Glushkov, who had received political asylum in Britain after being jailed in Russia for money laundering and fraud, was found dead at his home in New Malden, southwest London on Monday.
Scotland Yard said its Counter-Terrorism Command is leading the investigation "because of the associations Mr Glushkov is believed to have had."
Police say there is "nothing to suggest any link to the attempted murders in Salisbury, nor any evidence that he [Mr Glushkov] was poisoned."
Nerve agent attack
Former Russian spy Sergei Skripal and his daughter Yulia were poisoned with a nerve agent in the city earlier this month - an attack that Britain has blamed on Moscow.
Russia has denied any involvement.
Earlier, Russia's Investigative Committee, which reports directly to President Vladimir Putin, announced it had opened a murder investigation into Mr Glushkov's death.
On the Salisbury case, the committee said in the same statement that it will probe the "attempted premeditated murder" of Yulia Skripal, adding it was ready to co-operate with the British authorities.
One of Mr Glushkov's friends was late Russian oligarch Boris Berezovsky, who fled to London in 2000 following a row with Vladimir Putin.
Mr Glushkov had also worked for Mr Berezovsky's LogoVAZ car company.
He was arrested in 1999 and put on trial for allegedly embezzling $7m (£5m) from Aeroflot, and sentenced in 2004 to three years, three months in prison.
Russian media said he was granted political asylum in Britain in 2010.
But his case was revived by a Moscow court last year, which sentenced him in absentia to eight years for allegedly embezzling more than $122m (£88m) from Aeroflot.
The Russian embassy said it had sought Mr Glushkov's extradition in 2015 "for committing a number of severe financial offences on the territory of Russia," but the British government refused.
After Mr Berezovsky was found hanged in the bathroom of his Berkshire home in March 2013, Mr Glushkov told The Guardian he would "never believe" his friend took his own life.
An inquest into Mr Berezovsky's death recorded an open verdict.
Mr Berezovsky was also a friend of Russian dissident Alexander Litvinenko, who was poisoned with radioactive polonium-210 in London in 2006.
Police and MI5 are expected to examine allegations that a series of deaths on UK soil, including the Berezovsky case, may be linked to Russia.