A teenager stabbed to death outside a block of flats in west London has been named as 17-year-old Abdirashid Mohamoud.
The boy was discovered with stab injuries outside apartments on Union Lane, Isleworth, at around 10.35pm on Friday.
He was pronounced dead at the scene a short time later.
Scotland Yard said Mr Mohamoud, from the Brentford area, was chased by his attackers.
Detective Chief Inspector Richard Leonard said: “Our enquiries have established that the victim was in Syon Park close to the flats with a group of other people.
“A vehicle pulled up and a group of males got out. They chased the victim and attacked him in Union Lane.
“I need to speak to anyone who was in the park or the surrounding area at around 10.30pm on Friday night or who has information that could assist this investigation. They should get in touch immediately.”
A couple who called the police described finding the bloodied victim on the ground, and said they had heard shouting and looked out of their flat to see the teenager being assaulted by two people.
The pair, neither of whom wished to be named, said one of the perpetrators had his face covered.
The husband, a 33-year-old engineer, said: “It was one guy who was massive with, like, a mask on his face and another small guy. They were kicking him (the victim), but it was dark so it was hard to see exactly what was happening.”
By the time the couple went downstairs to the scene they said the two attackers had left.
His wife, 35, added: “The boy was bleeding from the mouth. The blood was everywhere. He was still alive, there was someone else there trying to help by checking his pulse. He was responding but he couldn’t speak.”
Her husband said: “It’s sad that he died.”
No arrests have been made.
Police said they remained open-minded about the motive for the killing.
Anyone with information is asked to contact officers on 101, quoting incident number CAD 8396/22Mar, or call Crimestoppers anonymously on 0800 555111.