Two knives were dumped after a street fight that left a 17-year-old dead, Scotland Yard has said.
The teenager was chased by the knifemen along a busy north London street in a well-known gang area, before he was repeatedly stabbed in the chest.
Chief Superintendent Nick Davies said victim Nedim Bilgin was 'well known' to police.
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Speaking at Islington Police station he said: "We’ve had dealings with him before. He was on our indices - as a missing person. We do not know why this was."
The senior officer said a fight in Caledonian Road escalated into the stabbing that left Nedim dead.
"We were called to a fight on the street, we do not know how many people were in the group at this time,” he said.
"Two knives were recovered from the area. We hope that these were the weapons involved in the incident.
"We are keeping an open mind about it being gang-related. It’s a real serious issue for us to look at.”
Victim Nedim Bilgin. Image: Metropolitan Police
Chief Superintendent Davies said multiple calls came in about fights in the area.
"There were a number of calls concerning fights in the Caledonian Road area, we were there within a matter of minutes,” he said.
"So far there has been speculation of a robbery gone wrong, but we do not think that is the case.
"There is clearly been some sort of fight, I do not know what was in the minds of the young men.
"Nedim was tragically killed last night. I won't go into the details as it is distressing for the family.
"He had multiple injuries. The post-mortem is to be carried out on Friday.
"We are always looking for more people. We are satisfied the people involved have been arrested, everything falls into that at this stage.”
A 'number of weapons' were recovered, Chief Superintendent Davies said, but he did not confirm if the murder weapon itself was found.
He said: "We always want to keep a big crime scene. It’s because suspects fled. Weapons were recovered in the area.”
He said a motive had not yet been determined, and urged anyone with any information to come forward.
"We keep an open mind in terms of the motive. We received a lot of calls that night from people in the area reporting weapons and fighting.
"A lot of people saw what happened, I urge you to talk to please come forward to help us solve this crime.
"It’s not a single thing for us to solve but more importantly, we let people know in the area what is happening.
"Anyone that has information please come to us directly, or use Crimestoppers anonymously."