A forensic expert at the scene in London yesterday (Image: Stefan Rousseau/PA Wire)
Alex Smith was held down screaming by three hooded thugs who had chased him through an estate plagued by drug problems. Witnesses told how he vainly banged on the door of a house pleading for help - and said that after he had been stabbed his attackers got in a car and drove past him laughing. Last night Scotland Yard detectives were carrying out a forensic search at the scene in Munster Square, Camden, north-west London.
The attack, only a short distance from Regent's Park, horrified foreign tourists staying at a nearby four-star hotel. It was London's 80th homicide this year and came as Prime Minister Boris Johnson promised to make Britain's streets safer with an overhaul of policing and justice.
Mr Johnson has promised to toughen jail sentences, hire 20,000 more police officers and allow them greater powers to stop and search suspects.
Residents had watched in horror from flats overlooking the scene as the victim was chased and surrounded.
They said he hammered on a door screaming, "Help me", before slumping to the ground fatally wounded at 11pm on Monday.
One onlooker told the Daily Express: "It was really horrible. I saw it all from my bedroom.
"There were three of them chasing this one boy. They were all wearing hoodies and the middle one out of the three was carrying a machete. It was really long.
"They held him down and stabbed him.Then they got into this silver Ford and drove past again just to laugh at him. It is so sad. They were so young."
A staff member at a nearby cafe