If you were to imagine the type of person who would kill a woman and her young son, torch his own house, and then kidnap the woman’s teenage daughter, you’d probably picture a hulking, tattooed ex-convict or a shaggy-bearded antisocial misfit with a crazy look in his eyes.

Probably the last person you’d picture would be James Lee DiMaggio -- a bland, pleasant-looking 40-year-old telecommunications technician, whose LinkedIn profile touts his expertise at Microsoft Excel and his customer service skills, and whose Facebook page -- since removed -- included inspirational quotes from Albert Einstein, Steve Jobs and poet Maya Angelou.  He was a longtime close friend -- “Uncle Jim”-- of the family he allegedly victimized.

Puzzlingly, the San Diego area resident -- whom FBI agents killed in a gun battle in the Idaho wilderness last Saturday when they rescued his captive, 16-year-old Hannah Anderson -- seems, at least outwardly, like the antithesis of the deranged predators who inhabit our nightmares.

According to Intelius, an online public records database, DiMaggio had no prior criminal record in California, and he owned the three-bedroom home that he allegedly set afire after killing his two victims.

San Diego County Sheriff Bill Gore admitted to reporters: “When you get a completely irrational act like we've seen here with two murders and a kidnapping, sometimes you might not be able to come up with a rational explanation.”

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But that leads to an even more troubling question. If an apparently normal person -- that is, someone who is functional in everyday living, with no history of violent acts or mental disturbances -- can suddenly morph into an arsonist, killer and kidnapper, what are the chances that any one of us similarly could go off the deep end and erupt into extreme violence?

While there’s little specific research on the subject, crime statistics suggest that the chances of an everyday person suddenly morphing into a brutal killer seem fairly slim. According to a 1997 U.S. Bureau of Justice Statistics study, the average American only has about a 5 percent chance of being sentenced to prison for committing any sort of crime in his or her lifetime.

If a person has managed to stay out of such trouble until his or her 40th birthday -- as DiMaggio did--the rate drops to lower than 1 percent. The same study showed that fewer than 6 percent of those incarcerated for the first time have killed someone.  And the “normal” person who takes more than one life, as DiMaggio allegedly did, must be rarer still.

A 2003 study by Northeastern University researchers James Alan Fox and Jack Levin found that only 3 to 4 percent of all acts of homicide involve multiple victims.

It’s impossible to rule out that an ordinary person might someday commit extreme, irrational violence. But in most cases, a seemingly normal killer probably isn’t really as normal as he might seem, explains Dr. Alan J. Lipman, a licensed clinical psychologist and founder and director of the Center for the Study of Violence in Washington, D.C.