A teenager who was stabbed to death in west London has been named as 17-year-old Abdirashid Mohamoud.
He was discovered with fatal knife wounds outside apartments on Union Lane, Isleworth, at about 22:35 GMT on Friday.
A post-mortem examination found Abdirashid, who was from the Brentford area, died from his injuries.
Police say the motive for the murder is still unclear and no arrests have been made.
Det Ch Insp Richard Leonard, who is leading the investigation, 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."
Officers arrived at the scene and gave first aid but could not save the teenager.
Scotland Yard has appealed for anyone who was in the Syon Park area at the time to come forward.
A couple who called the police said there was "blood everywhere".
The 35-year-old woman, who did not want to be identified, said Abdirashid was still alive when she and her husband saw him.
"There was someone else there trying to help by checking his pulse. He was responding but he couldn't speak," she said.
Her husband, a 33-year-old engineer, said the victim was assaulted by two people, one wearing a mask.
"It was one guy who was massive with a mask on his face and another small guy. They were kicking him, but it was dark so it was hard to see exactly what was happening."
Halima Abubaker, 22, said she saw two males "running for their lives" around the time of the incident.
She said: "I just heard loads of people, then there was seven police cars and two vans."
Victims in 2019
Motives and circumstances behind killings have varied - as have the age and gender of the victims.