A murder investigation is underway in North London after a shop worker who was critically injured following an assault in Mill Hill died in hospital.
While formal identification awaits, officers say they are satisfied the deceased is Vijay Patel, 49, from the Colindale area.
Next of kin have been informed.
Detectives arrested a 16-year-old boy on suspicion of murder late on Monday January 8. He has been taken to a north London police station where he remains in custody.
The investigation was launched after police were called at about 11.45pm on Saturday January 6 by the London Ambulance Service to reports of a man who had been injured on The Broadway, NW7.
Officers arrived at the scene and found Patel lying injured on the pavement outside a convenience shop. The officers took over first aid from members of the public who had stepped in to help.
The London Ambulance Service arrived and Vijay was taken to a central London hospital where he subsequently died at 17pm on Monday January 8.
Detectives have established that Patel had been at work in the convenience shop, together with the owner of the shop. Three teenage boys came into the shop and tried to buy some items including cigarette papers. Due to concerns about their age they were refused service after they were unable to provide suitable identification.
The three were unhappy about the decision and became aggressive, threatening to vandalise the shop.
As such Patel and a colleague went outside after them to ensure no damage was done to the shop. Patel was struck once by one of the teenagers, causing him to fall to the floor.
The colleague was also punched by the teenagers. He suffered minor injuries, but did not require hospital treatment
The three were seen to run off along The Broadway in the direction of Mill Hill Broadway Station.
The three suspects have been described as a black male teenager wearing a red sweatshirt, black jeans and white trainers; a black male teenager wearing a dark grey or black tracksuit and black trainers; and a black male teenager wearing a dark coloured hooded sweatshirt and black jeans.
Detective Inspector Ian Lott, from the Homicide and Major Crime Command, said: "At this stage we believe this to be an unprovoked spontaneous incident sparked entirely by refusal to let the suspects buy what they wanted.
"A man has lost his life for no reason other than trying to uphold the law. If you know who they are, or where they are, please get in touch and tell us their names.
"If you saw the three running away from The Broadway and where they went, let us know.
"I would like to thank the witnesses who have already come forward and told us what they saw. However, I would still urge anyone who is yet to speak with us, or who has captured some of the incident on camera, to come forward to help us. If you saw something that may help but haven't yet spoken to police, then please get in contact with us."
Detectives are continuing with house-to-house enquiries and capturing CCTV.
Patel's family are being supported by specially trained family liaison officers.
Anyone with any information about the identity of the three suspects or their current whereabouts is asked to contact the Incident Room on 020 8358 0200, or call Crimestoppers anonymously on 0800 555 111.