The death of a prominent Kremlin critic on British soil is now being treated as murder, Scotland Yard has announced.
Russian exile Nikolay Glushkov, 68, was found dead at his home in Clarence Avenue, New Malden, south-west London on Monday.
The Metropolitan Police were called to the scene at 10.46 pm and initially said the death was being treated as unexplained.
But a post-mortem investigation, which began on Thursday, concluded he was killed by compression to the neck, the force said.
Despite chilling parallels with the attempted poisoning of former Russian double agent Sergei Skripal and his daughter barely a week earlier, detectives said at this stage there was nothing to link the two attacks.
There was also no evidence that the businessman was poisoned, the force said.
A murder investigation has been launched, led by the counter-terrorism command, who will retain primacy "because of the associations Mr Glushkov is believed to have had", the Met said.
Mr Glushkov was outspoken after the death of his close friend Boris Berezovsky - another enemy of Russian President Vladimir Putin.
Mr Berezovsky was a friend of murdered spy Alexander Litvinenko and a thorn in the side of the Russian regime.
He was found hanged in the bathroom of his Berkshire home in 2013. An inquest recorded an open verdict.
Mr Glushkov told the Guardian in 2013 he would "never believe" he took his own life.
He was a retired financial director who had lived at his address for two years, Scotland Yard said on Friday.
The force said: "Detectives are retaining an open mind and are appealing for any information that will assist the investigation into Mr Glushkov's murder to contact them in confidence on 0800 789 321.
"In particular they are appealing for anyone who may have seen or heard anything suspicious at or near his home in Clarence Avenue, New Malden between Sunday March 11 and Monday March 12 to contact them.
"There are no wider public health concerns in relation to this investigation."