Detectives investigating the death of a Gloucester man say it is now "very likely" two people were involved.
Keith Soons, 36, was stabbed in the head in Cheltenham on 5 February. Police believe his iPhone 4 had been stolen and he was trying to recover it.
Mr Soons was found in Wellington Lane in Pitville, Cheltenham. He was taken to hospital but died later.
Three men, aged 26, 27 and 28, all from Cheltenham, were arrested on suspicion of murder and released on bail.
Det Supt Simon Atkinson said police wanted to trace a car seen at 0300 GMT driving into Pitville Lawn, turning around and driving away.
The two suspects are described as white, with one taller and stockier than the other. Both were in their late 30s.
"We need to speak to both men as they may have vital information," said Mr Atkinson.
Over the weekend officers handed out leaflets in Cheltenham town centre and to football fans at Cheltenham Town's game.