Three stabbings, including two murders, on the same night in north London are being linked by detectives.
A teenager has been arrested on suspicion of murdering two men who were stabbed to death in Camden on Tuesday.
The 18-year-old has also been linked to another attack on the same evening in which the victim survived.
Four other men, aged 24, 23, 20 and 21, were arrested on suspicion of grievous bodily harm and have been released while inquiries continue.
The first stabbing occurred near a block of flats on Aldenham Street in Somers Town at about 20:00 GMT.
The 16-year-old victim, who remains in hospital, and another youth are believed to have been chased by at least three men.
Half an hour later Abdikarim Hassan, 17, was found with fatal injuries in Bartholomew Road, Kentish Town, then at 22:13 Sadiq Adan Mohamed, 20, died in the third stabbing of the night.
The Metropolitan Police say Mr Mohammed and a friend were "chased by a group of four men" before the stabbing on Malden Road in Belsize Park.
Appealing for information, Det Ch Insp Paul Considine said: "What is clear is that there were three violent attacks, by a group of men armed with knives, within about two hours of each other and within about a mile of each other.
"I can understand why some people may be reluctant or nervous about coming forward but we need your help. We will treat your information in the strictest of confidence.
"Two families are suffering a terrible loss, and you could hold the answers to what happened to their sons, brothers, loved ones, best friends."
Ch Supt Nicholas Davies, who is in charge of policing in Camden, said a Section 60 order, which allows stop and search "with good reason", is still in place.
He said: "My officers have been on the streets using this power really effectively, seizing knives, stopping cars of young men carrying weapons and making arrests.
"That will continue for as long as we have the intelligence it is necessary."