As the police enter an abandoned house, a nauseating stench invades them. The room is dark and it looks like no one has been here in months. They enter further into the house and start seeing bloodstains on the floor. They follow this trail down the stairs to the basement where the smell becomes overpowering, causing some officers to flinch and run back up the stairs. In the basement they find the remains of several boys who had been molested and severely mutilated. What could lead someone to participate in such horrendous acts? What kind of person is capable of carrying out such evil acts? Serial killers have always aroused public curiosity and concern. People seem to be fascinated and disgusted by their horrendous crimes. The stories make newspaper headlines, and their gruesome murders are the subject of popular films and best-selling books. In this article I will discuss the causes that push a human being to become a serial killer. Although social scientists have developed many theories to explain the mind of a serial killer, scientific evidence supports theories of sociopathy, psychopathy, sadistic fulfillment, childhood abuse, and genetics. The Federal Bureau of Investigation defines a serial homicide as the killing of several victims in ten or more separate incidents over a long period of time (Dietz 483). Serial killers are often classified into specific categories. One category is motive; killers with motive are sexually sadistic killers or insane killers. The psychology of the killer is another category used to characterize these criminals. These types of killers are classified as sociopaths and psychopaths. This article will focus primarily on killers of the psychotic and sexually sadistic type, as these are the ones the public and media tend to focus on. According to James Fox and Jack Levin (19), serial killers are almost always Caucasian males who are in their twenties and thirties. Although there have been reported cases of female serial killers, the field is predominantly made up of men. There are two key characteristics of a serial killer, one is the presence of sociopathy or aggressive antisocial behavior. It has been estimated that nearly three percent of males in our society may be sociopaths. Most socio-paths are not violent: they can lie, cheat or steal, but rape and murder are not necessary. information on the genetic makeup of a serial killer. The public is disgusted by the bloody deeds committed by serial killers, but they will forever intrigue us. The fascination arises from the fact that in most cases murderers are so similar to the ordinary person. From the outside they seem normal like everyone else. Fortunately for humanity, others are not capable of such horrible actions. These serial killers are often psychopathic or sociopathic people who were abused as children. Others may seek to satisfy their sadistic fantasies aroused by their childhood experiences. The most recently identified reason is a link to a genetic predisposition to violence. The inherent goodness of human beings can sometimes go awry and lead to a person as evil as a serial killer. No matter how you analyze killers, they are not normal in any sense. Edmund Kemper, when asked what he thought when he saw a beautiful woman walking down the street, replied, "Part of me says, 'I'd like to talk to her, go out with her.' The other part of me says, 'I wonder what his head would look like on a stick?'” (Ming Ho).