POLICE are continuing to scour CCTV footage from cameras monitoring a busy motorway where a biker was murdered - shot once in the back of his head as he left a motorcycle festival.

Detectives are still trying to trace a green Rover 620 car over the shooting on the M40 near Leamington Spa, at about 2.15pm on Sunday.

A post-mortem examination on the body found the biker - said to be aged in his 30s and from the south of England - died from a single pistol shot to the head.

The man, who has not yet been officially named, was attacked in broad daylight as he rode home from the Bulldog Bash motorcycle festival.

Warwickshire Police said they believed the fatal shot had been fired from a handgun.

The motorway remained closed yesterday as officers conducted a search of the road.

It is believed the victim was a Hell's Angel in his 30s, from south London, who was shot after visiting the Bulldog Bash 20 miles away at the Long Marston airfield, near Stratford.

Police closed the road northbound between junctions 10, at Ardley, and 14, near Warwick.

Drivers were directed along a diversion to link up with the A43 to Northampton, where drivers can link up with the M1.

The M40 was also shut southbound between junctions 15 and 12.

A police spokesman said detectives had ruled out a road rage-type attack and were treating it as murder.

Officers want to trace a green Rover 620 car seen travelling south on the M40 close to a group of motorcyclists at around the time of the incident. Police would like to speak to the driver and occupants of this car.

The spokesman said the force was opening inquiries into whether or not the biker had been specifically targeted.

The Bulldog Bash is billed at Europe's number one biker party and attracts tens of thousands of motorcyclists and music fans from across Europe. This year Status Quo headlined the event.

The biker's death is not being linked to any incidents at the Bulldog Bash.

Bulldog Bash organiser, 56-year-old Hells Angel "Bilbo", said: "I knew the lad and you couldn't wish to meet a better person.

"We are used to deaths as bikers because people die in accidents. But we don't expect someone to get shot.

"This is murder plain and simple and we have no idea why this happened. We're just devastated.

"It's dangerous to guess why. This year was a massive event and it went off virtually trouble-free.

"We had an amazing weekend and then this happened and it has totally shaken everybody. It's a massive loss to the biker community as a whole."

The victim was travelling south with two friends and air ambulance crews were called to treat the man at the scene of the incident between junctions 13 and 12 on the M40 in Warwickshire shortly after 2.15pm yesterday.

Inspector Patrick Devereux of Warwickshire Police said the road would remain closed so a full forensic operation could be carried out in daylight.

Up to 400 cars were stuck on the motorway yesterday afternoon after police sealed off the area, but by the evening all had now been allowed off the motorway to continue their journeys.

The Highways Agency is advising motorists to avoid the motorway and take their journeys, if possible, on the M1 or M6 instead.