The 16-year-old boy was arrested on suspicion of murder on Monday, 16 November. He remains in custody at a north London police station.
Police were called at 3.50pm on Thursday, 12 November to Northwick Park in Harrow, following reports of a stabbing close to the underpass leading to Northwick Park Underground Station.
Officers attended, and a 17-year-old was found suffering from stab injuries. He was given first aid at the scene by officers prior to the arrival of the London Ambulance Service. Despite the best efforts of emergency services, he was pronounced dead at 16:31hrs.
He has been named as Jamalie Maleek Deacon Matthew, who was from the Harrow area.
His next of kin have been informed.
Detectives from the Specialist Crime Command (Homicide) are investigating.
Anyone who has information, video or images that could assist police is asked to call the incident room on 020 8358 0100 or via 101 quoting reference Cad 4735/12Nov.
If you don’t want to speak to the police, contact Crimestoppers on 0800 555 111. They are a totally independent charity and you remain 100 per cent anonymous, they never ask your name and they cannot trace your call, your IP address or the device you use.