- Video report by ITV News Correspondent Sejal Karia
Counter-terror police are treating the death of a prominent critic of Vladimir Putin as murder, Scotland Yard has announced.
Nikolay Glushkov, 68, a Russian businessman exiled in the UK, was found dead in his New Malden home, south-west London, on Monday.
Investigators initially said his death was being treated as unexplained.
But a post-mortem examination on Thursday concluded that he was killed by compression to the neck, the Metropolitan Police confirmed.
The investigation comes as counter-terror police continue to probe the nerve agent attack on ex-Russian spy Sergei Skripal and his daughter Yulia, widely attributed to the Kremlin, in Salisbury.
At this stage, however, detectives have refused to link the two attacks.
Despite this, counter-terror police are overseeing the Glushkov investigation "because of the associations" he had.
- Who was Nikolay Glushkov?
Exile Mr Glushkov had been living in the UK for two years.
As well as being an outspoken critic of Russia's president, he was also a close friend of late Russian businessman Boris Berezovsky.
Berezovsky himself was sometimes referred to as Putin's "enemy No 1".
Mr Glushkov was also friendly with Alexander Litvinenko, another ex-Russian agent who died in the UK, allegedly at the hands of Moscow, in 2006.
When he was seeking political asylum in Britain, Mr Glushkov's lawyer told a court that his client was "very close" to Berezovsky.
Berezovsky was found hanged in the bathroom of his Berkshire home in 2013. An inquest recorded an open verdict.
But Mr Glushkov told the Guardian he would "never believe" he took his own life.
Both Mr Glushkov and Berezovsky had been charged by Moscow with conspiracy charges in relation to laundering millions of dollars from the Russian national airline Aeroflot, where the former was deputy director.
The accusations, dating back to 2000, led to Mr Glushkov spending more than three years in a detention centre and facing two trials before fleeing to the UK.
Detectives say they are maintaining an "open mind" in relation to the investigation and appealed for anyone with information to contact them.
"There are no wider public health concerns in relation to this investigation," police said in a statement.
- Anyone with information can call police on 0800 789 321.