Police were called by the London Ambulance Service (LAS) just before 15:30hrs on Monday, 23 January to reports that a 15-year-old boy had been stabbed in Doyle Gardens, NW10.
Officers attended and found the boy suffering from stab injuries.
He was taken by the LAS to a central London hospital where he died. Next of kin are aware and are being supported by specially trained family liaison officers.
Whilst detectives believe they know who the deceased is, they await formal identification.
A post-mortem examination will be held in due course.
Detectives arrested a 15-year-old boy at an address in Norbury at 13:30hrs on Tuesday, 24 January.
He remains in custody at a north London police station.
An incident room has opened under Detective Chief Inspector Mark Lawson of the Homicide and Major Crime Command.
DCI Lawson said: "I would like to thank all those witnesses who have come forward and spoken to police. They have been of huge assistance to our investigation.
"However, if there is anyone out there who knows or saw something then please do get in touch with us, if you haven't yet spoken to police.
"Whilst establishing the motive is a key part of our investigation, at this stage we do not believe that the murder was linked to gang activity or membership.
"A 15-year-old boy remains in our custody and the murder investigation is continuing to move at a fast pace."
The 15-year-old allegedly screamed ‘he’s going to stab me’ repeatedly whilst his attacker chased him.
Any witnesses or anyone with any information is urged to contact the incident on room on 020 8358 0200 or via 101 or by tweeting @MetCC
To give information anonymously contact Crimestoppers on 0800 555 111 or visit crimestoppers-uk.org
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