According to members of Hasan's family, the Army psychologist, a devout Muslim with misgivings about the war in Iraq, was teased about his religion and called a "camel jockey" by other members of the military.
Finding radical Islam, whether sought out or contacted from within, "gives them a purpose," Garrett said.
"It gives them a focus. It gives them a singular focus that no matter what, this religion is about everything else," he said.
ABC News learned after the Fort Hood shooting that Hasan had exchanged 18 e-mails with al Qaeda leader Anwar al Awlaki, some of them asking when a jihad is appropriate and if it would be okay to kill American soldiers.
Officials are now saying Adbulmutallab has ties to Alwaki, an outspoken andmilitant Islamic cleric.
New information about Abdulmutallab's time at University College London suggests he was just one of many students immersed in what some have called pro-radical, anti-Western propaganda.
While at UCL, Abdulmutallab found refuge in the university's Islamic Society and he became its president. During his time as head of the Islamic Society, Abdulmutallab brought in speakers who talked about jihad.
The way terrorist leaders influence recruits is not unlike the cults that prey on people's insecurities and vulnerabilities, Garrett said. And with people like Hasan, Abdulmutallab, even the 9/11 hijackers, already immersed in the teachings of Islam, tipping their sensibilities becomes even easier.
"When you become isolated and you become depressed nothing looks bright to you," he said. "They get someone to tell them, 'We have the right way for you to go here.'"
And, he said, terrorists know to promise their potential recruits something they desperately are looking for -- acceptance.
"They promise a bright after-life," he said. "By dying for a cause like this makes you a better spirit, a better person, a better whatever."
But Dr. Howard Bursztajn, co-founder of the Harvard Medical School Program for Psychiatry and the Law, told ABC News that the loneliness apparently suffered by people like Abdulmutallab is of their own making and their own refusal to accept anything different from themselves.
"It's a self-imposed loneliness, a self-imposed isolation," he said.
"The fundamental question that we can ask in forensic psychiatry when we see a horrible act is, was this person simply bad or is he mad?" Bursztajn said. "People who are bad, the badness comes from a sense of self-righteousness, a sense of entitlement, a conviction that you somehow have a direct line to God."
Dr. Carole Lieberman, a psychiatrist with the University of California at Los Angeles Neuropsychiatric Institute and author of the book "Coping With Terrorism," said radicalist views, for many of the modern-day terrorists, including several of the 9/11 hijackers and Abdulmutallab, seem to crystallize with a foreign education.
Sept. 11 hijacker Mohamed Atta attended university in Germany as did Marwan al Shehhi and Ziad Jarrah. Mastermind Khalid Sheikh Mohammed attended Chowan College in North Carolina before transferring to North Carolina's A&T State University.