Russian police are working with Scotland Yard on a major criminal inquiry for the first time since the diplomatic fallout over the death of dissident Alexander Litvinenko.
The Metropolitan Police confirmed it was receiving help from Russian counterparts in the hunt for the suspected would-be assassin who shot wealthy banker German Gorbuntsov.
Detectives leading the investigation also revealed they had found a weapon, said by sources to be a pistol.
Officers are still searching for a Hackney cab driver who dropped Mr Gorbunstov off at his executive block of flats shortly before he was gunned down.
Mr Gorbuntsov remains "critical but stable" under armed guard in hospital after the attack near Canary Wharf, east London.
Scotland Yard said it was "too early to speculate" on Russian reports the attack could be a gangland hit linked to a murder attempt on another banker, Alexander Antonov, in Moscow.
The assistance of Russian authorities with the investigation marks a warming of relations since the 2006 murder of Mr Litvinenko, who had accused security services of carrying out terror attacks to help bring Vladimir Putin to power.
British prosecutors named former KGB agent Andrei Lugovoy as the main suspect in the dissident's killing, but Russian authorities have repeatedly refused to send him to the UK.
Mr Litvinenko, 43, died of radioactive polonium-210 poisoning in November 2006.
Mr Gorbuntsov was shot a number of times as he entered his block of flats by a suspect described as white, 6ft and slim.
He was wearing a dark hooded top and was seen running from Byng Street away from Westferry Road, towards Marsh Wall.
A force spokesman said: "The shooting is not thought to be gang-related or linked to any other incidents in Tower Hamlets.
"Officers retain an open mind regarding the motive for the attack at this time."
The victim previously owned banks in Russia and Moldova, according to Russian media.