Police are trying to establish why a pedestrian who was found dead on the M6 in Cumbria was on the carriageway.
John Alan Lewis, 48, of Chorley, Lancashire, was seen walking on the southbound carriageway near Carlisle early on Tuesday, Cumbria Police said.
He was hit by a number of vehicles and police said they were treating it as a fail-to-stop collision.
They said they had traced a number of the drivers involved and were treating them as key witnesses.
Insp Andy Wilkinson said: "Our focus is now firmly on establishing the circumstances that led Mr Lewis to be on the carriageway.
"We believe that there will be other people who were driving between junction 44 and 43 during the early hours of Tuesday morning that will hold key information that can help us find answers."
Car keys were found at the scene which he said may have been connected to Mr Lewis, and they were searching for any abandoned vehicles in the area.