Murder, rape, satanism and necrophilia is the staple diet of millions of teenagers who listen to the lyrics of extreme heavy metal music.

This World investigates the potential links between "death metal" and a series of gruesome crimes around the world.

In Italy a group of young death metal fans formed a satanic cult called the Beasts of Satan.

At least four gruesome killings resulted.

Michele Tollis, whose son Fabio was one of the those killed, is convinced of the link between the music and Fabio's death.

"No one can contradict me when I say that heavy metal and satanism are closely linked. They're inseparable," he says.

But death metal musicians deny that they have any responsibility for the actions of people who profess to be their fans.

"I say don't blame people like me and (Marilyn) Manson, because we never said: 'Hey, we're going to be role models for all your kids.' That ain't what this is about. It's about entertainment," says Glen Benton of US metal band Deicide.

With exclusive access to the families, one of the killers and graphic police footage, the film tells the inside story for the first time.

We hear from the musicians, the children and the parents from Oslo to California and ask just how far can music go in its ability to shock, and just how damaging might it be?