First aiders who helped out at a crash scene in Sheffield are being urged to contact South Yorkshire Police.
Officers believe the good Samaritans could assist with the probe into the crash in which 25-year-old Karl Marsden died earlier this month.
He was in a black Vauxhall Zafira which crashed on Station Road, Halfway, at 11.40pm on Saturday, July 1.
South Yorkshire Police said the car was travelling towards Killamarsh, collided with fencing and then left the road.
Mr Marsden was pronounced dead at the scene and a 31-year-old man also inside the Zafira suffered serious injuries.
He was taken to hospital but has since been released and is recovering at home.
Two men, aged 31 and 25, have been arrested on suspicion of causing death by dangerous driving and have been released under investigation as enquiries continue.
A South Yorkshire Police spokeswoman said: "Members of the public provided vital first aid assistance at the scene of the collision prior to emergency service crews arriving and police are keen to speak to them, as they believe they could assist with their investigation.
Anyone with information should call South Yorkshire Police on 101.