UK police have launched a murder investigation after the death of Russian businessman Nikolai Glushkov in south-west London.
Mr Glushkov was found dead at his home in New Malden on 12 March.
A post-mortem examination revealed Mr Glushkov, who was 68, died from “compression to the neck”.
There is, at this stage, no evidence linking the death to the attempted murder of a former Russian spy and his daughter in Salisbury, police say.
Detectives are retaining an open mind and are appealing for any information that will assist the investigation.
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 11 March and Monday 12 March to contact them.
Police on Friday continued to guard the home lived in by Mr Glushkov. A blue and a purple tent was erected to cover the front drive of the property, which has been cordoned off along with several adjoining properties either side.
Mr Glushkov is the former deputy director of Russian state airline Aeroflot.
He was jailed in 1999 for five years after being charged with money laundering and fraud.
After being given a suspended sentence for another count of fraud in 2006, he was granted political asylum in the UK in 2010 and became a critic of Russian President Vladimir Putin.
Former PR and advertising executive Lord Bell, who was a close friend of Mr Glushkov, described him as a “very charming, funny, affectionate man who had a troubled past”.
He said he was “concerned” his friend’s past might have made Russia consider him to have worked against the state.
Kate Fitzsimmons, an 87-year-old neighbour of Mr Glushkov, said he was “just an ordinary friendly Englishman” who would wave at her across the road.
She said his death and the subsequent police activity was a “big shock”.
Mr Glushkov had a close friendship with fellow Russian businessman Boris Berezovsky, who came to the UK in 1999 after falling out with Mr Putin.
Mr Berezovsky was found hanged in the bathroom of his Berkshire home in 2013 and an inquest recorded an open verdict.
Meanwhile, Russia’s investigative committee has said it has opened a criminal case investigation into “the murder” of Mr Glushkov and the “attempted murder” of Yulia Skripal.