I read a lot of true crime books (especially about serial killers) because killing for recreation is the most bizarre concept I have ever encountered. I don't remember the book title, but one was about Dennis Nielsen. He was asked about how he dismembered the bodies without making a real mess of his living quarters. He very matter of factly walked the police through the process. It was something along the lines of "You just go into the kitchen and slit open four large garbage bags and tape the pieces together. Put the body in the center of the bags and dismember it. Afterwards, just fold up the bags and you have no blood to clean up." He dispassionately discussed this like you or I would unclogging a drain. (Ironically, that is how he was caught.) The human mind is capable of sublimely beautiful creations like poetry and music, and also the utter depravity that drives a person to kill for pleasure.
I would like to add one book to you to those of you who like true crime. It is KIller, the biography of Carl Panzram. I won't go into details if anyone wants to read it, but I will say there are people who think they are bad, and then there are people like Panzram who are Bad.