Serial killers can also be classified by their organizational and social skills. They can be organized or disorganized (depending on the type of crime scene) and nonsocial or asocial (depending on whether they are excluded by society or exclude themselves). The following chart illustrates behaviors of the two most common types.
The majority of identified serial killers are organized and nonsocial. Most of them also follow some other basic patterns. More than 80 percent of serial killers are male, Caucasian and in their 20s or 30s [source: Hickey]. Serial killers are generally intelligent, and they usually kill Caucasian women. There's no way to "tell" a serial killer simply by his appearance -- most of them look like everyone else. Ted Bundy, who was convicted of 30 murders, was often described as attractive, charismatic and articulate. John Wayne Gacy was a popular figure in his community and often performed as a clown at block parties. He met with first lady Rosalynn Carter when he was precinct captain of his local Democratic Party. He was also convicted of the murders of 33 boys and men.
Often, serial killers exhibit three behaviors in childhood known as the MacDonald triad: bed-wetting, arson and cruelty to animals. They are also likely to have come from broken homes and been abused or neglected. Although some are shy and introverted, others are gregarious and outgoing but actually feel very isolated.
Many theorists point to the troubled childhoods of serial killers as a possible reason for their actions. We'll explore this and other theories for why they do it in the next section.