Detectives were hunting for two men seen running away after a man was shot dead outside a London prison.
Scotland Yard said the 20-year-old victim was pronounced dead at the scene by paramedics at Wandsworth prison in south-west London.
The shooting happened in the prison car park at around 2.30pm. A witness reported seeing two men wearing motorcycle crash helmets acting suspiciously just before the attack.
Police could not confirm that the dead man had been at the prison to visit an inmate, nor how many shots had been fired.
The witness said that two men had appeared to be waiting in the street outside the prison entrance.
The woman, who did not want to be named, said: "I saw two men in the street. They made me nervous. They were wearing motorcycle helmets with the fronts pulled down over their faces.
"They were apart from each other in the street right outside the entrance. One was sitting on a wall.
"I thought they were cash van security guards. That is when I heard several bangs. I thought they were gunshots. There were at least four. One of the staff members said there had been a shooting.
"I could hear sirens. By the time I left the shop there were police and ambulances everywhere."
A Metropolitan police spokesman said: "We were called at 2.30pm to Heathfield Road after reports of a man shot outside the prison. On arrival we found a man with gunshot wounds. Ambulance staff were treating him at the scene. He subsequently died.
"Two men were seen running away from the area." Searches were ongoing in nearby streets, he said.
A London Ambulance Service spokesman said: "We were called at approximately 2.30pm to reports of a shooting on the Earlsfield Road.
"We sent two single response vehicles and two ambulance crews, an officer and an air ambulance doctor in a car.
"Sadly, an adult male patient was pronounced dead at the scene."
Wandsworth prison is one of the largest jails in England and Wales. Built in 1851, it is currently able to hold 1,416 prisoners.
