Britain: Police found the body of a near-decapitated man in his 60s yesterday when they were called to an incident in the Swiss Cottage area of north London.
"At this stage we believe the victim was assaulted in the street," a police statement said.
A police source initially said the man had been beheaded with an axe. Officers later reported they did not believe the man had been decapitated, but had suffered severe head injuries.
"I saw a policewoman being sick," witness Nick Blackford (20) told Sky News, adding he thought the weapon had been a small hand-axe.
"It is a really, really bad thing to have to see. Everyone is really, really horrifically shocked how something like this could have happened here."
Swiss Cottage is an affluent neighbourhood, and Mr Blackford said the road where the attack had occurred was a "nice residential area".
A man in his 30s was arrested at the scene, and is being questioned by detectives.
Mr Blackford, a student, said he saw a man with blood on his hands give himself up to armed police after the incident.
He said he was awoken yesterday morning by the sounds of screaming in Eton Avenue. He described how the head of the victim, a man in his 60s, was turned to "mush" by the ferocity of the assault.
Two men from a nearby building site were also at the scene, carrying what appeared to be iron bars in an attempt to stop the assailant, but were too late.
"The police came out and arrested him at gunpoint. He had blood on his hands. He dropped the axe on the floor. There was a dustbin lid on the floor. I think either he was using it or more likely the victim was using it to protect himself.
"The victim was on the floor. I saw a guy lying down with a huge, flat red mushy mess instead of a head, just across the road. It is horrific. You never want to have to see that situation. It shocked me quite a lot."
Neighbour Margaret Mikkelsen (29) told how people confronted the assailant and tried to stop him. "I heard shouts, and I saw a couple who had stopped their car and were shouting at the man who was just standing there with an axe.
"He was just standing there; I could see the victim was dead and he was lying face-down.
"A man who lives in my building was telling him to put the axe down. Then two men grabbed scaffolding poles to try to stop him hurting anyone else. But he didn't respond to all the people shouting at him."
Then police arrived, she said. "People were shouting at him to put the axe down, and he put it on the floor.
"Then they had him with his hands cuffed behind his back. It was really scary."