Blood has been found at a house in Adelaide's northern suburbs and police believe it was where a 19-year-old man was stabbed before being driven to hospital where he later died.
Superintendent Des Bray says the house has been locked down and will be forensically tested.
A task force, bringing together major crime and organised crime detectives, has also been established to investigate the death which has been declared a major crime.
Supt Bray says the murder investigation is proving difficult for detectives.
"With most murders we have a scene to start from," he said.
"Where this one, it's taken most of the day to establish where it most likely occurred."
The dead man was dropped off at the Lyell McEwin Hospital at about 9.50pm (CDST) on Wednesday but died soon after from his injuries.
Police have spoken to two women who were in the car, but they continue to offer no assistance.
They may face charges.
The male driver of the car ran off and, despite an extensive search, has not been found.
The black Holden Commodore used to take the man to hospital has been seized while an autopsy on the dead man is also being conducted.