Police launched a murder inquiry tonight after a dying man was found when officers pulled over a van.
The fatally injured man was found in the back of the white van when it was stopped in Sunningdale, Berkshire, shortly before 2pm.
Eyewitnesses said the shoeless victim, who is believed to have been badly beaten, died at the scene after four men were arrested.
A large section of the A30 London Road, near its junction with Cedar Drive, remained cordoned off tonight.
Thames Valley Police said four people were arrested on suspicion of murder after the body was found.
A spokesman said eyewitness reports that a second man also died at the scene were incorrect.
Marketing manager John McCann, 38, said his wife Samantha, also 38, was hit by a blood-covered gunman as he tried to escape police.
He said: "As she came out from an alleyway on to the road, she bumped into somebody who was one of the armed suspects.
"She noticed that there were three others already in custody, handcuffed by police and surrounded, and this guy was running away.
"The man was eventually caught and she thinks four people were eventually taken into custody."
He added: "The rumour at the scene is that it is some sort of kidnap attempt but we do not know any more than that."
Asked how his wife was, Mr McCann added: "She is fine. She was not scared or intimidated because she just thought someone bumped into her.
"She had her back to him and it was only afterwards police told her he was armed with a gun."
Eyewitnesses said the dead man was wrapped in bags and one officer at the scene remarked he appeared to have been tortured.
The body remained at the scene, on the pavement beside the road, covered with a green tarpaulin and forensic tent.
Witnesses said a sledgehammer was recovered from the van, a 1999-registered Mercedes Sprinter diesel.
A police helicopter hovered overhead for several hours and an air ambulance was called at about 2pm.
Amanda Bealin, of estate agency Hamptons, said the incident took place between 2pm and 3pm just along the road from her branch.
"The police took three people out of the van and cuffed them on the floor," she said.
Ms Bealin added that she believed a fourth man in the front of the van fled the scene as the others were being held.
David Redding-Lang, 52, landlord of the Sunningdale Lounge, saw the drama unfold outside the pub.
He said: "I was up in the office and I noticed a van being pulled to the side of the road by a patrol car.
"I thought it was just a minor offence, the van was a bit shabby.
"The next time I turned I saw the police chasing someone down the road. There were three other men on the ground. I later saw the police bring back the fourth man."
Mr Redding-Lang said the arrested men were in their 40s or 50s and were held by plastic handcuffs.
He added: "I could see a body underneath the van, the van is directly opposite and I could see the body on the floor. The person had no shoes on and was very still."
Another eyewitness who saw the van being stopped said: "We saw a white van pulled on to the side of the road by police and then three men being led around the side of it and into a police car.
"They didn't struggle, they just got out. There weren't any sirens or screeching of brakes. It didn't seem like a chase."
Another said: "No shots have been fired in front of us. I saw some gunmen being chased by the police."
South Central Ambulance Service said police called in paramedics at about 2pm, reporting a man had been assaulted and was breathing shallowly.