Police were called at 23:33hrs on Thursday, 29 June to Elthorne Road, N19 to reports of a stabbing.
Officers responded with paramedics from the London Ambulance Service.
A 15-year-old boy was found with stab wounds. Despite the efforts of medical staff he was sadly pronounced dead at the scene, just after midnight.
He has been named as Leonardo Reid from Islington.
It was established that another victim, a 23-year-old man, had also suffered stab injuries. He had been taken to a west London hospital, where he too was pronounced dead.
Officers have informed the next of kin of both victims. They are being supported by specially trained officers.
Special post-mortem examinations for both victims have given a provisional cause of death as a stab wound to the chest.
A third victim, believed aged 28, was also located at an address in N19. He had suffered a stab wound. He was taken to a north London hospital where he remains. His condition is not thought to be life threatening.
Detectives from the Specialist Crime Command are leading the investigation, supported by colleagues from the Central North Command Unit.
A 46-year-old man [A] was arrested on the afternoon of Saturday, 1 July on suspicion of murder and attempted murder. He was taken to a north London police station and was subsequently released with no further action.
Detectives investigating a double murder in Islington are renewing appeals for witnesses to come forward as their investigation continues.
Detective Chief Inspector Jim Eastwood, said: “We’re three days into our investigation, and whilst enquiries are ongoing, I still need to hear from anyone who was in the vicinity of Elthorne Road on Thursday night.
“Two people have lost their lives through an act of violence and it is vital that we get the answers their families so desperately need.
“I know that there are people who are yet to come forward. I would ask that you consider the feelings of those whose lives have been impacted upon by these senseless murders and make contact with us.