The 25-year-old Alexandra man remained in a serious condition in Dunedin Hospital's intensive care unit last night.
He was taken to hospital by helicopter after the incident on State Highway 8 between Clyde and Cromwell.
Sergeant Derek Ealson said police could ''look at the matter in its entirety'' after the examination and investigation were completed.
He could not comment on certain aspects of the incident because of the risk of prejudicing the investigation, he said.
Police still needed to talk to some independent witnesses.
They had spoken to the six male and three female occupants of the van, who ranged in age from 18 to 25.
Members of the public had commented on social media they had seen a van travelling in Alexandra and Roxburgh earlier on Saturday with a man hanging from a window.
Sgt Ealson said witnesses had approached police about the incident.
He asked anyone with additional information to contact Alexandra police.
Sgt Ealson said the injured man's family were being supported by police and Victim Support.
''Their [the family's] focus at the moment is with their son and loved ones.''
