Police are hoping a couple may have vital information as to how a man fell from a moving taxi in Bristol.
It is believed that a man and a woman travelling in a burgundy Ford Fiesta car, or similar, witnessed the incident on Frenchay Park Road, in Broomhill.
The couple, both white in their early 20s and of slim build, helped the 19-year-old man from Stapleton. They then left before police arrived.
The victim remains in a critical condition at Frenchay Hospital.
From other witnesses, it is believed the taxi may have been a silver colour.
Anyone with information on this incident is asked to contact Avon and Somerset Police.