Serial killers are the most difficult to understand or, rather, the reasoning behind their actions are difficult to comprehend. The drives behind these killings can vary from case to case. Fetishes and hatred of the opposite sex can be motivators in these killings.
Two facts can be agreed upon by experts about serial killers. First, serial killers generally prey upon their preferred sex; for example, homosexual serial killers will seek out same sex victims, as in the case of Jeffrey Dahmer, bi-sexual killers- both sexes and heterosexual killers choose the opposite sex. Secondly, as a serial killer continues in his killing spree and he becomes more experienced, violence in the killings tend to escalate. There are no known cases of a serial killer starting out by dismembering his victims and, later, deciding that poison would be better.
The reasons for a serial killer beginning in this path can vary. In most cases, there was some sort of abuse or trauma in this person's life, at some point. Chemical imbalances of some sort may, also, be attributed to these sorts of crimes. Some killers may simply have been born with this need to kill.
Serial killers are, generally, difficult to catch and the reason may be this: there are two types of mad men. The first type are those we see on the streets. The observer may know that this person is imbalanced and that their behaviors are unacceptable, but they do not. The second type is the person, who knows that their fetishes and behaviors are unacceptable. This person keeps his behaviors concealed and carries on a sort of "double life". This second type of madman is the more dangerous of the two. He is the next door neighbor, who one does business with or has contact with everyday, whom one would never expect to be a calculating killer. When he's caught, all who know him are shocked to the point of disbelief. Yet, he may even have been caught red-handed. Ted Bundy was a fine example of this very type.
Serial killings have been recorded as early in history as the 1800's; they continue to this day. Unfortunately, there is no crystal ball in existence that can aid authorities in predicting who might become such a killer.