A fourth man was arrested tonight by police investigating a fatal shooting outside a prison.
Darcy Austin Bruce, 20, from Fulham, was gunned down outside Wandsworth Prison, south-west London, on Friday afternoon.
Three men, aged 19, 22 and 26, were later arrested on suspicion of being involved in the murder but released on bail last night.
A 27-year-old man was arrested in south London today and is currently in custody, Scotland Yard said.
It is believed Mr Bruce was visiting the prison when he was shot dead. A post-mortem examination gave the cause of his death as multiple gunshot wounds to the torso.
Police said they are keeping an open mind as to the motive.
Two men wearing crash helmets were seen running away from the scene of the attack in Heathfield Road after a series of gunshots were heard.
Officers from Operation Trident, which investigates gun crime in the black communities, are investigating.
Police have asked anyone with information to call Crimestoppers anonymously on 0800 555111.
Wandsworth is one of the largest prisons in England and Wales. Built in 1851, it can hold up to 1,644 category-B prisoners.