Frederick Moody, 18, was ambushed close to a senior politician's house and left to die in front of his young sister. Witnesses claimed they had heard the killers shout "leave him for dead" before fleeing the scene in Guildford Road, Stockwell on bicycles.

A 16-year-old was arrested this morning in Brixton over the killing. Frederick, known as Freddy, stumbled down the road before collapsing from stomach wounds. It is the fifth teenage knife killing in less than a month and comes after a major drive by Met commissioner Sir Ian Blair and Mayor Boris Johnson to tackle the problem.

It is believed Frederick was attacked by a gang of youths who had been waiting outside his home - four doors down from the house of Edward Garnier QC, the Tory shadow minister for justice.

Vida Oblitey, a neighbour who described Freddy as like a son to her, said she had been with his mother when he died in hospital last night. She said: "Freddy was a very handsome boy, a lovely boy - and whoever has done this has taken the only son away from a very happy family."

Ms Oblitey, 52, added: "I had just come home from work and got a call from my kids - they said Freddy had been stabbed. After rushing back I phoned Freddy's mother, who I was with until 5am this morning. I had been at the hospital with her and we were there when it was confirmed he had died."

She said Frederick had been studying at Kingston College. "We rushed to St Thomas' to meet his mother. Frederick was in a very bad way. We do not know anything about the attack, only that there was a knock on Frederick's door."

He had just left his home when he was attacked shortly after 7pm. Residents, including local GP Dr Balaz, desperately tried to treat the teenager before paramedics arrived. He was declared dead at 10.15pm.

Cynthia Smith, who lives opposite the scene, told how she first thought it was her son who had been stabbed, as she ran into the street. She said: "I thought it was him. I was panicking, shaking. I ran into the road and saw the boy. It was not my son.

"He was lying there on the pavement. There was not much blood - it was internal. It was a horrible moment. My friend Evelyn had her hands on him, putting pressure on, trying to stop the bleeding. He had his eyes open and was talking to the police. I don't know what he was saying.

"When I first saw him I thought he was dead. The paramedics were working on him for about an hour, putting the oxygen mask on and pumping his chest."

Another witness and neighbour, Sharon Smith, 23, said she and her boyfriend ran out of her house after hearing shouts and screams. She said: "He was murmuring and his eyes were just rolling into the back of his head. We were trying to keep him with us."

Friends today told how Frederick had just finished his studies and was trying to enter a construction trade apprenticeship scheme. A family friend said: "I am a decorator and he had asked me for a reference as he was planning to go into the construction trade. He wanted to start on some kind of project.

"He had been in a bit of trouble when he was younger but he wanted to better himself. He wanted to work. He was a good, genuine guy. He was fun-loving and a lot of people loved him. He was not a trouble maker. His life was snatched away."