Part of the M1 will be closed today while police officers make a fingertip search of the central reservation for clues to amurder.
Officers hunting the killer of a woman stabbed to death while walking her dog plan to close the motorway for at least two hours from 10.30am.
Witnesses have said they saw a bare-chested man running across both sections of the carriageway towards a housing estate from the place where Anne Cook, a Web designer from Watford, was murdered last Tuesday. Several drivers said they had to swerve to avoid hitting the man, who was carrying a white shirt or T-shirt.
The 35-year-old was stabbed through the chest after being attacked as she walked her dog along a wooded path off Munden Drive, Hertfordshire.
The M1 closures will affect one northbound and one southbound lane between junction five, the Watford exit, and junction 6A, the St Albans turn-off.