The driver of a car towing a horse box may hold the key in helping police solve what caused an accident in which a teenager died.

Greg Stiles, 19, of Thame, was killed when his Ford Fiesta was in collision with three other cars on the A4129 Risborough Road, between Kingsey and Longwick, in Buckinghamshire, on Sunday, May 17.

His girlfriend, Abigail Dowdy, 18, remains in a critical condition at the John Radcliffe Hospital, in Oxford

A 4x4 vehicle was also involved in the collision, but did not stop.

Police have appealed for help from the public to trace the vehicle.

Investigating officer Pc Phil Hanham said: “We are trying to trace the driver of a vehicle towing a horse box that was travelling between Kingsey and Towersey that afternoon between 2.30pm and 3pm.

“We are making contact with local riding stables in the area and distributing leaflets in the hope that it might jog someone’s memory. We would urge this person to come forward as they may have some vital information that might be able to help us with our investigation.”

A 25-year-old man was arrested on suspicion of causing death by dangerous driving and released on bail until July.

Anyone with information should call police on 08458 505505 or Crimestoppers on 0800 555111.