Osama bin Laden is wanted for several deadly terrorist bombings.
FBI

Still at large: Abdul Rahman Yasin, indicted for the 1993 bombing of the World Trade Center. THAT effort failed.
Department of State

The children's flower memorial at the Murrah Federal Building in Oklahoma City, site of a domestic-terrorism bombing in 1996.
FEMA

Composite drawing and photograph of Timothy McVeigh, executed for obliterating the Murrah Building.
FBI

Liberation Tigers of Tamil Eelam have used suicide bombers in their quest to carve a Tamil homeland in Sri Lanka.
Special Operations

But can psychology, the study of the mind, tell us what motivates terrorists and how they differ from you and me? The Why Files talked to three people who have tried to get inside the heads of furtive killers.

Scientifically, it's a tough task, since terrorists don't volunteer for psychological studies. At any rate, terrorism experts differ in their understanding of motivation. We'll present three opinions without pretending to say which is most compelling -- or whether other answers would be more convincing.

Anger without guilt
For 30 years, Rona Fields, a Washington, D.C. psychologist, has been psychologically testing terrorists and paramilitaries from Northern Ireland, Israel, the West Bank, Lebanon, Southeast Asia, and Africa. She thinks today's suicide terrorists share the still-born moral and emotional development she saw in the Khmer Rouge, who created a bloodbath in Cambodia during the late 1970s. "Their definition of right and wrong is very black-and-white, and is directed by an uthoritative director," says Fields. "There's a total limitation of the capacity to think for themselves."

A terrorist develops gradually from a young age, Fields says. The boys (typically aged 10 to 16) who are easist to recruit for suicide terrorism are "at the stage of development of moral judgment called retributive justice or vendetta." This "an eye for an eye" stage of emotional development was described by the Swiss psychologist Jean Piaget, she adds.

In "societies where there's been intergenerational, intercommunal war," Fields says, many adults never outgrow the vendetta, and are trapped in righteous indignation, which Fields found among "all the members of all paramilitary organizations I examined. They believe there's a difference between right and wrong, but when they do something in the name of the cause, it's justified."

These true believers, she adds, "are angry, but they don't feel guilty about their anger."

Highly rational?
In contrast to the popular sense that suicidal terrorists are sociopathic whackos, many experts argue that they are effectively pursuing their goals.

"They are rational, they are not insane," says Richard Pearlstein, associate professor of political science at Southeastern Oklahoma State University. "They have goals and they are moving towards those goals."

Not only are terrorists not crazy, but they don't share a personality type, wrote David Long, former assistant director of the State Department's Office of Counter Terrorism. "No comparative work on terrorist psychology has ever succeeded in revealing a particular psychological type or uniform terrorist mindset."

Still, Long wrote that terrorists tend to have low self-esteem, are attracted to groups with charismatic leaders, and, not surprisingly, enjoy risk. Oddly, Long concluded that many terrorists are ambivalent about violence and guns (see "The Anatomy..." in the bibliography).

Long wrote just before the ongoing wave of suicide attacks, where a focus on raising the death toll has superseded the desire to score a political point or free imprisoned comrades.

What's different with the suicide bombers?