Another link between criminology and terrorism is recidivism, the tendency toward relapse. "Terrorist groups and terrorist countries tend to be recidivist," LaFree said.
"My guess is, 75 percent of the incidents are from about 20 countries,'' he said of the 70,000 incidents in the database. "We're trying to get as close to those countries as we can get."
Where terrorism and other crimes diverge is in their goals, LaFree said. Terrorism, unlike common crime, is usually rooted in political goals.
Jonathan Wilkenfeld, a professor of political science at Maryland and a principal investigator at the new center, theorizes that terrorism recruits tend to be loners, on the fringe of society, similar in some ways to the young men recruited by religious cults in the United States.
"My sense is, these groups are composed of people who even within their own societies are outliers in some respects," Wilkenfeld said. The Sept. 11 hijackers, he said, "were relatively well-educated, not particularly poor individuals in their own societies who for some reason were outcasts and outside their own societies and came under some kind of influence."
Terrorist organizations tend to arise among groups that are "marginalized, discriminated against and persecuted within [their] own society," Wilkenfeld said. Alternately, they can form within a group "whose members are dispersed into what we might call a diaspora, who are alienated from the society in which they find themselves."
Terrorist groups of the 1970s and 1980s often were rooted in Marxist ideology and saw their enemy as capitalism, said Arie Kruglanski, a professor of social psychology at Maryland and the third principal investigator. Today's terrorist groups draw more on religious and national or ethnic ideologies and on anti-American sentiment, he said.
Many of those sentiments are widespread in Arab nations, Kruglanski said, but the desire to express them violently might not be.
"You can be opposed to American policies and yet be opposed to terrorism," he said. "One does not necessarily translate to the other."
Terrorist organizations train recruits with a "series of psychological triggers that, step by step, make you capable of hurting fellow human beings," Kruglanski said. This is partly a matter of inhibiting compassion and defining a population as the enemy, he said.
One possible public misconception of terrorist groups is that they behave irrationally or senselessly, Kruglanski said.
"Unlike individuals, organizations tend to be more rational in a way, and they weigh very carefully the efficiency of a given tactic under the circumstances," he said. In order to choose terrorism, a group would "have to assume that, under the circumstances, terrorism is their best bet. And this may rest on the notion that terrorism is going to be effective."
