Forensic psychiatrist Dr. Helen Morrison shared intriguing data about serial killers, whom she's extensively profiled over the last 25 years. Typically, neighbors and relatives are shocked to find out that someone they know is a serial killer, she said, as the person doesn't give off any external clues. John Wayne Gacy is a perfect example of this, she added, as he acted neither suspicious nor crazy.

Mass murderers have motives such as revenge, Morrison explained, but serial killers commit their heinous acts without motive or emotional meaning.From her studies, she has concluded that serial killers do not become the way they are from any particular traumatic incident. Rather, she believes they have a genetic predisposition for this and that something occurs during adolescence that triggers their brain chemistry. Usually, they first kill as a teenager, and then wait for a period before committing another murder, she detailed.

The behaviors and mindsets of serial killers are so similar as to be like "cookie cutters," said Morrison, who estimated there may be as many as 60 of them living in America today. They often have a sense of self-importance, she noted, and may contact the media because "they want to let people know they're there."

Letters from Serial Killers

First hour guest, actress Amanda Swisten, has had a long standing interest in abnormal psychology. A year and a half ago she received an unsolicited letter from a convicted serial killer which began a correspondence between them. The death row inmate, whom she declined to identify, has confessed to 10 murders, she said.

In The Serial Killer Letters published in 1998, a young mother named Jennifer Furio corresponded with 14 infamous serial killers and included their unedited responses in her book. Read an excerpt from the chapter on Edward Spreitzer.