A van driver died in a motorway crash after a piece of concrete "around the size of a house brick" hit his windscreen, causing him to lose control and hit a tree, police said.
Police are treating the death on the M11 near Birchanger, Essex, as suspicious and said one line of inquiry is that the item was thrown from a bridge over the motorway, but that officers were keeping an open mind.
The driver, in his 60s and from Sible Hedingham in Essex, died at the scene.
His Vauxhall Corsa van struck the central reservation barrier before it left the road on the nearside and hit a tree.
Essex Police were called to the northbound carriageway of the M11 between junctions seven and eight at 4.50pm on Wednesday and the carriageway was closed for investigations.
The Goose Lane bridge, which crosses the motorway, was also closed as part of the inquiry and officers want to speak to drivers who saw anyone acting suspiciously on the bridge.
Detective Chief Inspector Martin Pasmore said: "Telling a family they have lost a loved one is always extremely difficult and my thoughts are very much with the gentleman's family at this very distressing time.
"Having carried out forensic examinations at the scene, we are treating his death as suspicious because a piece of concrete - around the size of a house brick - was found to have struck the windscreen.
"We believe this caused the driver to lose control of the van and leave the road shortly after passing the Goose Lane bridge.
"As part of our inquiries, we closed the bridge at Goose Lane, and the one about a mile and a half before it, to carry out forensic examination work.
"We are keeping an open mind as to how the concrete came to strike the windscreen and there may be a number of explanations as to how it ended up inside the van.
"Our inquiries will be far-reaching and at this stage it is too early to say what the cause was."
Police are also appealing for witnesses and for people to send dash cam footage taken in the area, between the junctions for Harlow and Bishop's Stortford, between 4pm and 6pm on Wednesday.