A teenager was shot dead as he ran through a housing estate trying to escape a gunman, neighbours said today.
The 17-year-old victim died in a stairwell at a block in Peckham, south east London, yesterday afternoon.
Witnesses said he was desperately banging on the closed door of one eighth-floor flat before the fatal shot rang out.
Two other teenagers, one aged 17 and another 18, suffered stab wounds as a group of young men ran amok on the estate.
Detectives from Scotland Yard's Trident unit were investigating whether the murder and stabbings took place during a clash between rival gangs.
Three male suspects, all believed to be aged in their teens, were arrested at the scene and were being questioned at south London police stations.
Residents said violence linked to notorious gangs had surged on the Pelican Estate in recent months.
The gunshot victim was found dying in a stairwell at Heron House after reports of an attack at about 4.30pm yesterday. He was pronounced dead at the scene.
Police were then led to a 17-year-old boy with a stab wound who had run to a flat in nearby Gannet House. He was taken to hospital where his condition is stable.
The two blocks are a short distance apart, close to a mini football pitch and basketball court.
Hospital staff then called police to report a third victim, an 18-year-old man, who arrived with minor stab injuries. He has been discharged.
Samba Koroma, 40, a cleaning manager, said the dead teenager was seen banging on the door of an eighth-floor flat.
He said: "He ran into the building. He was knocking on that door for somebody to open up but nobody opened the door.
"I don't know whether the boy knew the couple (who live there). He ran down the stairs and I think that's when he got shot.
"We've got a lot of boys who come here to this estate. They just hang around. They are there every day and every night."
Police sealed off several areas on the estate as officers in forensic suits searched bushes and open ground.
Residents described Heron House as a magnet for trouble. One said: "They are out of control at Heron House. It's not a nice place to pass."
A mother-of-two who lives on the estate said gang crime had recently returned after appearing to end a few years ago.
She said: "I think it's pathetic. I keep my son indoors and he is 18. There's too much going on on the streets. It's not safe here at all.
"The police should be patrolling round here more often. An innocent life has been taken away. How will his parents feel?"
One man who lived near to the scene of the murder said it sounded like a firework but he instantly knew it was a gunshot.
The 43-year-old said: "I heard a loud bang at 4.20pm. I have never heard a sound like it before, but I knew it was a gunshot."
He later saw a large pool of blood beside a lift on the fifth floor with police officers standing beside it.
A Metropolitan Police spokesman said: "Officers are treating all three incidents as linked at this early stage and three males have been arrested in connection with the investigation."
The victim was the 19th teenager to be killed in the capital this year. A total of 15 were murdered last year and 29 in 2008.