Four people fled the scene of a motorway crash that killed a 27-year-old man, police said.
Officers are hunting for the people, who were in a Mercedes, and ran from the M40 crash site at about 1.15am on Saturday.
The collision, which happened on the northbound carriageway in Buckinghamshire, led to a closure between junction 1a for the M25 (Denham Interchange) and junction two for Beaconsfield.
The driver of the Golf, a 27-year-old man from High Wycombe, died of his injuries.
His passenger, also a man in his twenties, sustained serious, but not life-threatening injuries and has been taken to hospital.
There were four people in the Mercedes, two men and two women, who fled the scene on foot.
Thames Valley Police said a 26-year-old man from Beaconsfield has been arrested on suspicion of causing death by dangerous driving and possession of a knife in a public place – he remains in police custody.
Witnesses reported seeing the Mercedes being driven “erratically” just before the crash, investigating officer Detective Sergeant Edward Crofts said in a statement.
He added that the family of the 27-year-old who died in the collision are being supported by specially trained officers.
“I am appealing to anybody who was driving on that stretch of the M40 in the early hours of this morning and witnessed the collision to please get in touch with Thames Valley Police,” Detective Sergeant Crofts said.
He added: “I’m particularly keen to hear from anybody who saw either the Golf or the Mercedes travelling northbound just prior to the collision, as some witnesses have reported the Mercedes being driven erratically.
“I would also ask drivers to please check their dash-cams and contact us if it has captured anything that may be able to assist this investigation.”
Ambulances and fire crews attended the scene of the crash, and a diversion was put in place.
The Denham interchange is used by drivers travelling to London Heathrow Airport and travellers were warned of the possible delays.
The stretch of road was opened almost 12 hours after the crash at 12.30pm.
