Two more men have been arrested on suspicion of murder after a 16-year-old was stabbed to death last week.
Alex Smith was stabbed repeatedly in Munster Square, Camden, on Monday 12 after being chased by a group of people.
A 19-year-old man was arrested at an address in Camden on Saturday on suspicion of murder and is in custody, Scotland Yard said.
Another 19-year-old man was arrested at an address in Wembley, north-west London, on Sunday on the same charge and is also in custody.
The teen, from Brent, north-west London, died from a stab wound to the chest, a post-mortem examination found on Thursday.
A 23-year-old man and an 18-year-old man arrested on suspicion of murder on Wednesday have been bailed until mid-September, according to the Metropolitan Police.
A 20-year-old man arrested on Friday on the same charge was also released on bailed until mid-September.
A group of young men were heard "screaming and laughing" as they pursued Alex with a machete, according to witnesses.
He was heard shouting "help me" before collapsing near the doorstep of a family home, one witness said.
Alex died at the scene after police were called at 11.10pm.
His death marks the 90th murder inquiry opened by Scotland Yard so far this year. Fifteen of those victims have been teenagers, 14 of whom were fatally stabbed.
Neighbours told of the distressing scenes as the boy was pursued into the estate of family homes before being attacked.
Rosanara Begum, 55, said on Tuesday: “The boy was running away from them. Then we saw the two boys holding him and the other one stabbing him.
“As soon as I heard ‘Help me, help me’ I was on the phone to the ambulance. He was bleeding a lot.
"The attackers were skinny and just looked like teenagers. They were running off and they were screaming and laughing."
Her daughter added: “We saw three boys all wearing hoods all covered in black, the middle one had a long black machete type knife. It was really long."