The couple were found by a police patrol in the lay-by on the A6 at Deadman's Hill, near Luton, at 0645 BST today.

The dead man, who has been identified as physicist Michael John Gregsten, 34, from Abbots Langley in Hertfordshire, had been shot twice in the head with a 38-calibre revolver.

His companion, 22-year-old laboratory assistant, Valerie Storie, from Cippenham, near Slough, had been raped and shot five times in the chest. She was taken to hospital in Bedford where she underwent surgery for her injuries.

Car rally

Police believe the couple, both employees of the Road Research Laboratory near Slough, were confronted by a man with a gun as they were parked on Dorney Common in Berkshire yesterday evening.

They were ordered to drive to Deadman's Hill, where the attack took place.

The murderer left the scene in Mr Gregsten's grey Morris Minor, registration number 847 BHN, which was found abandoned in Ilford, Essex, this evening.

Detectives and tracker dogs have spent the day searching the surrounding area and so far two cartridges have been found.

House-to-house inquiries have also been carried out.

Miss Storie's mother, Mrs John Storie, said: "Michael came here last night and had tea with Valerie.

"They then left at about 7.30pm in a grey Morris car which I understood belonged to Michael's mother. They took with them maps and other things to organise a car rally being held at their office this weekend.

"Valerie has worked at the laboratory since she left school five years ago and she has known Michael for a long time."

Mr Gregsten's body was tonight identified by his wife, Janet. He leaves two sons, aged seven and two.

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