A 16-year-old boy is believed to have had a car driven at him before he was chased by four people and stabbed to death.
Drekwon Patterson was found with stab injuries in Preston Road, Brent, north-west London, shortly after 11.30pm on Thursday.
The teenager, from the Wembley area, was treated at the scene and taken to hospital but died on Friday morning.
No arrests have been made.
Police have released images of a car and a van in relation to their investigation.
They are appealing for information about a car seen driving from the scene which was later discovered burnt out.
Detective Chief Inspector Richard Leonard, from the Metropolitan Police, said: “I need to hear from any witnesses or anyone with information about this tragic murder – if you know anything that may be significant, please get in touch.
“In particular, I need to find out more information about a car – a black Ford Mondeo, using registration number YR54 NHN – which was seen on CCTV driving away from the scene and found burnt out in Silver Jubilee Park, NW9 on Friday 19 February.
“I believe this car was used in an initial attempt to injure Drekwon in a collision on Preston Road.
“After the Mondeo had been driven at him, Drekwon ran away and was chased by four suspects who had got out of the car, before being caught and fatally stabbed.”
He said the car is a “key line of inquiry” and described it as “a fairly large vehicle and quite old, so it would have been noticed”.
The officer said police are also keen to trace the driver of a van which was seen on CCTV stopping briefly near the scene.
He said: “I am appealing for that driver to please come forward as a witness.”