A 16-year-old boy was driven into by a car before he was chased by a group of four and brutally stabbed to death.
Drekwon Patterson was found with serious stab wounds in Wembley, North London at 11.30pm on Tuesday.
He was treated at the scene before being taken to hospital.
Despite the efforts of emergency services, he died shortly before 9am on Friday.
Metropolitan Police have released images of a car and a van in relation to the investigation.
They have called for information about the car, which was later burnt out.
Detective Chief Inspector Richard Leonard 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.
"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."
Police also want to trace the van's driver after the vehicle was seen on CCTV stopping briefly near the scene.
He said: "I am appealing for that driver to please come forward as a witness."
A murder investigation was launched the day that he died, which is being led by homicide detectives from the Met's Specialist Crime unit.
The latest update from police today confirmed no arrests have been made, but they are continuing to investigate.
Chief Superintendent Sara Leach, in charge of policing in Brent, said: "It is another tragedy that a boy of just 16 years old has died as the result of a knife crime."My thoughts are with his family at this time and my officers, alongside homicide detectives, are doing everything they can to identify and arrest those responsible."
Enhanced reassurance patrols will continue in the Preston Road area, CSI Leach confirmed, because of how "deeply affected" the community has been by the death of the teenager.
Anyone with any information is asked to call police on 101, quoting CAD 8167/18Feb, or information can be given anonymously to Crimestoppers on 0800 555 11