Police have named the young man stabbed to death in Neasden as Saif Abdul-Majid.
The 18-year-old, from Ealing, was stabbed to death in Tanfield Avenue around 3.50pm on Friday.
Despite the efforts of police and paramedics, he died at the scene.
A post-mortem determined he died of multiple stab wounds, police said.
The victim’s next of kin have been informed.
A 15-year-old boy was arrested on suspicion of murder on Saturday.
He has been bailed to a date in mid-October.
Det Chf Insp Nicola Wall from the homicide and major crime command is leading the investigation.
Any witnesses, or anyone with any information, is urged to contact the incident room on 020 8785 8244.
Call Crimestoppers anonymously on 0800 555 111 or visit crimestoppers-uk.org.
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