A fierce critic of Vladimir Putin, who was found dead at his south London home earlier this week, was murdered, police have said, amid fears of a second Russian sponsored attack on British soil.
Businessman, Nikolai Glushkov, 68, who was granted asylum in the UK after fleeing Moscow in 2006, was strangled to death, Scotland Yard has confirmed.
The former right-hand man of deceased oligarch, Boris Berezovsky, his death came just over a week after Russian spy, Sergei Skripal, and his daughter, Yulia, were poisoned by a nerve agent in Salisbury, reports Daily Telegraph UK.
The former boss of the state airline, Aeroflot, Mr Glushkov had told friends he feared he was on a Kremlin hit-list.
A former bodyguard, who worked for Mr Berezovsky, and knew Mr Glushkov well, said his death had all the hallmarks of a state-sponsored assassination.
The France based security expert, who asked to be identified only by his initials, RG, said: "I'm not at all surprised [that a murder investigation has been opened].
"You can easily choke someone in 10 seconds so that they fall into a comatose state and you can then continue strangling them without leaving any other marks on the body. It's a technique they [the Russians] know well."
Mr Berezovsky was found hanged in the bathroom of his Surrey home in 2013, with the cause of death being put down to suicide.
But suspicion has always surrounded the circumstances of his death, with many believing he was one of a number of Putin critics who were deliberately silenced.
Another of their close associates, Badri Patarkatsishvili, 52, died at his Surrey home in 2008, following an apparent heart attack.
A close personal friend of the three men, who asked not to be named, said he was in little doubt their murders were linked.
He said: "All of them were in no doubt that Boris was killed. It is perhaps inevitable that they would be assassinated themselves.
"It is a very horrible thing to happen, he was a lovely man, a very funny man with a great sense of humour. It sounds like somebody has a vendetta against them."
Counter terror officers continued to probe the nerve gas attack on Mr Skirpal, whose attempted murder led to the expulsion of 23 Russian diplomats from London.
Boris Johnson, the Foreign Secretary, escalated the war of words with Russia, when he accused Vladimir Putin of personally ordering the nerve agent attack.
He said it was "overwhelmingly likely" that the Russian President was behind the attempted murder, a claim that was described as "unpardonable" by Mr Putin's spokesman.
News of this latest murder investigation will further stoke fears that critics or enemies of Russia and its leader, are no longer safe on British soil.
Downing Street said the Prime Minister had been "kept informed" of developments but stressed that Mr Glushkov's death was a police matter and that no link had been made with the Salisbury poisoning case.
But Iain Duncan Smith, the former Conservative leader, said the murder of Mr Glushkov appeared to "fit into a pattern" of violent deaths of enemies of Mr Putin.
He said: "If there is a link between Mr Glushkov's death and the Kremlin it will be further proof that we are dealing with essentially a rogue state which refuses to abide by international rules and has violated UN laws.
"What has been going on is a deliberate attempt to settle Russian scores in the UK."
But a key ally of Jeremy Corbyn has suggested moderate Labour MPs who blame Russia for spy poisoning are "enemies" who should be deselected.
Chris Williamson, the Labour MP for Derby North, said Labour MPs who had decided Moscow was "unequivocally" to blame were "baying for blood" and he suggested they face de-selection.
And the Kremlin also ramped up its language, launching a withering response to Defence Secretary Gavin Williamson, who had suggested Russia should "go away and shut up".
Major-General Igor Konashenkov, a spokesman at Russia's defence ministry, accused Mr Williamson of engaging in "market wench talk", adding that it reflected his "intellectual impotency".