Mass murder is awful enough. But some serial killers not only embark on slaying to slake their perverted pleasures but enjoy the mutilation of their victims' bodies - and sometimes also revert to cannibalism.The simple act of slaying would sicken most people. Yet that is not sufficient a thrill for those who find the excitement begins once their victims are dead. Cutting up corpses is, of course, one way of disposing of the evidence. But here we examine the butchers who dismember for pleasure.They are monsters like Andrei Chikatilo, the so-called 'Rostov Ripper', who tortured, murdered, chopped up and sometimes cannibalised as many as 50 victims. Or they can be quiet unassuming perverts like Dennis Nilsen, whose London house of horrors so overflowed with body parts that they blocked the drains.There is nothing new about this, the sickest side of homicide, of course. The most famous serial killer of all was Jack the Ripper - and butchering maniacs have been slashing their bloody path through history ever since.