Police believe a biker might have have vital information about a collision between a van and motorcycle which left its rider critically ill in hospital.
Emergency services were called to the A419 in Gloucestershire at 1210 BST following reports of the accident.
"Officers are keen to speak to this person, described as riding a powerful bike, seen overtaking a lorry at the time of the accident," police said.
The injured man, a 56-year-old from Oxfordshire, was airlifted to hospital.
Great Western Ambulance Service said the victim suffered potentially life-threatening injuries.
"Paramedics worked with firefighters to free the patient who was trapped underneath the van.
"He suffered multiple critical lower limb and body injuries, including a broken femur.
"The van driver was not injured."
Police are appealing for anyone who saw the accident between the white Transit van and red Harley-Davidson at Chalford, near Stroud, to contact them.
The road was closed for several hours while the accident was investigated.