Schoolchildren hunting for clues at a mock crime scene staged by their teacher on a class outing in Florida stumbled on the last thing they expected to find - a real corpse.

The body belonged to a homeless man who had died, apparently of natural causes, in a corner of the Fort Lauderdale park the teacher, Sue Messenger, had chosen for the summer school exercise in criminology.

Forensic science has become extremely popular with the success of the CSI: Crime Scene Investigation television show and its many spin-offs. There were 29 pupils from St Thomas Aquinas High School combing through the grass on Monday.

The clues Ms Messenger had scattered around the park included paper skeletons, fake weapons, bullet casings and sunglasses, but her pupils spotted something she had missed - a human hand clutching at a fence.

"We thought it was Ms Messenger messing around with us," Josh Rozental, 16, who first found the body, told the Miami Herald.

"I thought it was fake," he told CNN. "I just thought it was like a really good wax hand or something. So I got the rest of our group and we got the camera. And my friend Billy Spreitzer came over and he didn't think it was fake, so he touched it and he turned very pale very fast."

They went to fetch Ms Messenger, who realised her pupils were trampling over a likely crime scene.

"When I went over, knowing what I know about rigor mortis and postmortem lividity, it was apparent to me that actually this was a deceased individual," she said. "So the biggest thing is I wanted them to move off ... I knew there was going to be an investigation and I just wanted them to back off and for us to not to disturb anything."

The Fort Lauderdale police described the dead man as a blond, white male and said there were no signs of foul play. "The students went up to this one area and found a man with his back against the wall and he looked dead. They thought it was part of the skit," Fort Lauderdale Police detective Kathy Collins told Reuters.

The man had not been officially identified yesterday so it was unclear how his life had brought him to a miserable end in the corner of a Florida park.

"Mostly, I wanted to get across to my students that this was a person. Especially with what's happening to the homeless people," Ms Messenger said. "I just wanted to make sure that the students understood that this is a horrible thing to happen."

Mr Rozental said he had got the message. "It was exciting finding what I found," he said yesterday. "I've never seen a dead body before, so at first we were just in denial because we just thought it was fake. After we found out it was real, it was disturbing. Just finding a dead body in a fake crime scene."