Paul Allen, 41, was fighting for life on Sunday after being gunned down at the property in northwest London on 11 July.
A witness said the victim was shot in the throat by an attacker who fired six times into the rear of the house in Malvern Drive, Woodford Green.
Armed police and paramedics were called to the scene of the shooting at 11pm and Allen was taken to hospital with gunshot injuries.
Allen was jailed for 18 years in 2009 for his role in the £53m heist at the Securitas depot in Tonbridge, Kent, in February 2006.
Scotland Yard said he remained in a critical condition as they announced a second arrest over shooting.
A 28-year-old man was arrested on Saturday on suspicion of attempted murder and firearms offences. He remains in custody.
Another man, aged in his fifties, was arrested on the same day on suspicion of attempted murder and firearms offences and has since been bailed to return on a date in mid-August.
The Metropolitan Police said officers were following a number of lines of inquiry and appealed for witnesses to come forward.
The witness, who asked to remain anonymous, said: “I was there outside just after the attack had happened. Neighbours had gathered outside the front of the house.
“The gunman had driven to the back of his house and gone through the garden. The back of his house is just a big window, so you can see inside clearly.
“Whoever it was then shot six times into the window. This was before all I see is police arriving, an ambulance and a Swat team with guns.
“We waited outside the house. Then I saw him taken out on a stretcher. He was covered in blood, on his stomach, his neck. The paramedics said that he had been shot in the neck.”
The man said a woman was in “hysterics” following and described the scene as “like something in a war film”.
Stand-up comic Kane, who lives in Manchester, is understood to rent out the house.
His spokeswoman said: “Russell’s thoughts are with the victim and his family at this terrible time. No further comments will be made whilst the incident is being investigated by the police.”
Allen was the trusted lieutenant of Lee “Lightning” Murray, who masterminded the Securitas robbery.
The heist saw a gang, some posing as police officers, kidnap the manager of the security firm’s depot and hold him and his family at gunpoint.
Police later recovered £21m of the missing cash, but the remaining £32m was never found.
Allen fled to Morocco with Murray before he was arrested after four months on the run.
He spent 20 months in Rabat prison before he was brought back to Britain to face trial in January 2008.
Allen, then a father of three, admitted charges of conspiracy to rob, kidnap and possess firearms in relation to the heist at Woolwich Crown Court in September 2009 as a retrial was about to begin.
He pleaded guilty on the basis that he was not one of the robbers who entered the depot, or one of the kidnappers, and did not handle any firearms.
He was jailed for 18 years and was later excused from paying back his alleged share during a secret court hearing.
Additional reporting by PA