Waltham Forest Police were called to High Street, E17 at 23:31hrs on Sunday, 7 May by London Ambulance Service (LAS) following reports of a stabbing.
The 17-year-old male sufferred a serious stab injury, and was taken by London Ambulance Service to an east London hospital were hee died in hospital a short while later.
The victim has been formally identified as 17-year-old Elijah Dornelly.
A post-mortem examination on Tuesday, 9 May, gave cause of death as a stab wound.
An 18-year-old man was arrested at an address in Uxbridge on suspicion of murder on Monday, 15 May. He has been taken to a north London police station where he remains in custody.
Detective Chief Inspector Matt Bonner, who is leading the investigation for the Homicide and Major Crime Command, said:
"This murder has left Elijah's family devastated. While we have made significant progress with our investigation into Elijah's murder, it is vital that anyone who saw this incident, or the events leading up to the incident, gets in touch.
"While work continues to piece together Elijah's movements prior to his murder, I would directly appeal for witnesses to come forward and speak to officers - you may hold valuable information to assist us in this investigation."
Any witnesses, or anyone with any information, are urged call the incident room on 020 8358 0400, or contact police via 101 or by tweeting @MetCC.
The victim was at anti-knife crime rally just hours earlier.
The wounded teenager was found near the junction of Buxton Road after reports of a row between youths in a supermarket car park.
DETECTIVES believe two men were “laying in wait” for the 17-year-old boy before knifing him to death in Walthamstow High Street.
Next of kin have been informed.
Ahmed Ahmed, 30, owner of Netcafe, said: “It was a fight in the Lidl car park.
“This is the area groups of young people get together. We have been asking police to do something about it.”
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