THEY BLEND IN. They don't make threats. They carefully plan their attacks rather than "snap." They may be quite sane.
Their friends, acquaintances and relatives sometimes know they are planning to plant bombs or shoot their victims, but say nothing to authorities in advance.
This is what I have learned about domestic terrorists and assassins by interviewing psychologists who currently work for and have worked for federal law enforcement agencies. Some of these psychologists have spent decades developing methods to identify potential attackers.
"We think it is more useful to pay attention to a person's ability to plan and execute actions than to focus on the question of whether the subject is mentally ill or not," said Robert A. Fein, a forensic and national security psychologist who spent more than 25 years working with the Secret Service.
The alleged Boston Marathon bombers demonstrated the ability to plan and execute an attack. They carefully planned how to make and trigger their bombs. We still have many questions about them, but one big one is whether others knew they were planning an attack but kept silent.
This is what psychologists call the "bystander effect."
"The bystander might be a family member, a peer, a colleague, supervisor or subordinate at work," said Fein. "In our study of school shootings, in about 80 percent of the attacks, other kids knew something bad was going to happen (but the) kids who knew rarely told adults."
Fein does not believe in profiling, but rather in studying patterns of behavior. When seeking out a domestic terrorist, he says, "if he is interested in extreme ideas, it doesn't say a whole lot because there are many people who hold or consider extreme ideas and never attack others." Fein and his colleagues have developed a theory of "threat assessment" through which law enforcement officials can ascertain "pre-attack behavior." "We encourage protectors and investigators to distinguish between persons who make threats and persons who pose threats," Fein said. "Of great concern are persons who pose threats who never make a threat."
(No person who has ever attacked a President, Fein said, "ever communicated a direct threat to the President, the Secret Service or to law enforcement." The alleged Boston Marathon bombers never made a threat as far as we currently know.)
"We found a number of people who wanted to do bad things, but didn't want to see themselves as criminals," a psychologist who works with federal law enforcement agencies told me. "They are murderers in search of a cause. They tell themselves, 'I want to change the world.' Some we give the romantic term 'terrorist.' They are people who want to do something bad, so they say it was for al-Qaida or a jihad."
Today, the anti-terrorism mantra for the public is: "If you see something, say something." But that, Fein points out, is advice usually meant for strangers, for people who don't know the potential killers. But what about those who do?
"What encourages people to come forward, and what blocks them?" Fein asked. "I am talking about co-workers or family members. How might people who have concerns be encouraged to come forward?"
I will be writing more about domestic terrorism and threat assessment in the days ahead. But the question of "ratting" on someone is a big, human and, therefore, messy problem.
A threat assessment expert who has worked with high government agencies put it this way: "As parents, we are in denial all the time about our kids' impulses. Who wants to think your kid is a murderer? Parents are paralyzed with either worry and fear or they are in denial."
But law enforcement officers trained in threat assessment have developed methods to glean the truth. One psychologist told me: "In the old days, if (Secret Service) agents were concerned about Johnny Smith, they would go to his grandma and ask, 'Is Johnny capable of killing the President?' But what grandma is willing to say yes?
"Instead, you ask grandma, 'Has Johnny done anything that concerns you?' And she says, 'Yes, he is disappearing on trips and won't tell me about it.'"
Another psychologist who has worked with law enforcement said: "I am working under the assumption that there were people who knew (in advance about the Boston bombings.) But would they come forward if they knew (the brothers) would be locked up for a long time?
"If I am parent, I may try to intervene with my son, take his computer away or something. But would I call authorities if he might end up in federal prison for 30 years? That is a tough, tough question.
Roger Simon is chief political columnist for Politico.