By Vivian Attwood

A person can kill another of their own free will. They do not need Satan to intervene. This is the view of a top police psychologist who warned people not to put too much emphasis on the so-called forces of evil.

Gerard Labuschagne, who heads South Africa's police investigative psychology unit, was commenting on the schoolyard slaying at the Nic Diederichs Technical High School in Krugersdorp on Monday where a schoolboy allegedly slashed a fellow pupil to death and injured three others.

"Whenever there is a murder people jump to conclusions, and always it is God or Satan who told the killers to do it. These notions should not be taken seriously," he said.

However, this has not stopped the growing belief that the hugely popular US heavy metal band, Slipknot, was at the root of the slayings.

The alleged killer used a mask that resembled that of a Slipknot band member.

He was also apparently a follower of the band's nihilistic music.

The music produced by Slipknot is either referred to as Nu Metal or Death Metal.

The band was formed in 1995 and was initially called The Pale Ones.

The name was later changed to Meld and then to Slipknot.

In December 1995 drummer Joey Jordison suggested that band members start wearing make-up to give them a more fearsome appearance.

All nine band members now wear weird masks instead of heavy make-up.

According to witnesses of Monday's attacks, Morne Harmse was dressed completely in black and wore a mask similar to that favoured by Slipknot's lead singer, Corey Taylor.

Fellow school pupils of the accused claimed in media reports that he was "possessed by Satan".

School killings are by no means a new phenomenon; nor are they restricted to the United States, although the US have logged up some of the most notorious cases, like the 1999 Columbine High School shootings, in which 12 students and a teacher were killed.

Between 1996 and the beginning of 2008, 187 people died in 38 school killings ranging in location from Scotland to Alaska, Yemen, Canada, New Mexico, the Netherlands, Germany, Sweden, Bosnia-Herzegovina, Argentina, Finland and the US.

The largest number of victims was recorded in the 2007 shootings at Virginia Tech where student Cho Seung-Hui, 23, went on a shooting rampage killing 32 and wounding several others, before taking his own life.

Although some school killers elsewhere in the world have claimed they were instructed by Satan to kill pupils and/or teachers, analysis of the killers' lives and personalities in the wake of their tragic deeds has frequently shown that the perpetrators were lonely, socially marginalised children who had exhibited unusual behaviour patterns before reaching violent meltdown.