A former Russian banker is in a coma after being repeatedly shot with an automatic weapon during an attack in London.
In hospital under armed guard, he is said to be in a critical but stable condition.
Detectives are treating the attack on the man, named by Russian media as German Gorbuntsov, as attempted murder.
Scotland Yard's Trident command, which investigates gang-related shootings, is understood to have liaised with overseas counterparts in the hunt for the gunman behind the attack on Tuesday evening.
Mr Gorbuntsov was shot several times as he entered a block of flats in Byng Street on the Isle of Dogs at around 7.30pm.
The attacker opened fire with a sub-machine gun, according to the Kommersant newspaper.
A suspect was seen running away from the scene towards Westferry Road.
He is described as white, 6ft tall, of slim build and was wearing dark clothing.
Tony Smith, 26, an estate agent, said he had been trying to drive down Byng Street moments after the shooting.
He said: "I pulled my car up and looked down and saw his body, saw him. Police were surrounding him but there were only two police cars, and the rest came later.
"The window was shot out on the door. I looked at him, I thought he had been stabbed at first. I didn't expect this to happen in this block."
Mr Gorbuntsov, who is in his 40s, previously owned banks in Russia and Moldova, according to Russian media.
Serviced apartments in the block of flats where Mr Gorbuntsov lived command a premium of £200 a day in rental income.
Scotland Yard said it was "too early to speculate" on Russian reports that the attack may be linked to a 2009 investigation into a murder attempt on another Russian banker, Alexander Antonov, in Moscow.
Three Chechen men were convicted of attempted murder in the case and given long jail sentences in 2010.
Local officers are patrolling the area in an attempt to provide reassurance to the community.
Any witnesses or anyone with information are asked to call the Met Police on 020 8733 4212 or, if you wish to remain anonymous, Crimestoppers on 0800 555 111.