Days after a mass shooting at the Fort Hood Army post in Killeen, Texas, details of the gunman's life have captivated millions looking for motives behind Maj. Nidal Malik Hasan's murderous rampage.
As military psychiatrist trained to counsel troops returning from combat, Hasan's personal history has sparked many theories about why he turned on the very people he was employed to counsel -- killing 13 and wounding at least 30.
Some see this as an act of terrorism, but crime experts and fellow psychiatrists familiar with the military question whether Hasan's alleged actions compare with those of George Sodini, who is accused of shooting 11 women in a Pennsylvania gym this summer, or Seung-Hui Cho 's motives in the 2007 Virginia Tech Massacre.
"What went wrong?" asked Dr. Paul Ragan, a former military psychiatrist and now a professor at Vanderbilt University. "I keep thinking of the psychology that we know about mass shooters -- the Texas clock tower shooter from 1966, Columbine and Virginia tech," he said.
According to Ragan, profiles of a mass murderer often cluster into age groups of teens and early 20s, "or they seem to be men in their early- to mid-40s -- disaffected in their careers, many of them are loners, they have poor social skills and poor interpersonal skills."
Mass murderers tend to come in two types, according to academic articles authored by forensic psychologist J. Reid Meloy. One type is predatory, premeditated and emotionless. The other acts out from anger, fear, or response to a perceived imminent threat or trigger.
Hasan is an American of Palestinian decent. Born and raised in Virginia, he went on to Virginia Tech and joined the U.S. Army to become a psychiatrist. His aunt, Noel Hasan of Falls Church, Va., told the Washington Post that he was single and had no girlfriend and that "he did not make many friends" and "did not make friends fast."
After Sept. 11, 2001, his aunt said Hasan was harassed about his Islamic faith and had sought for several years to be discharged from the military.
Dr. Amir Afkhami, an assistant professor at George Washington University, was shocked at the violence Thursday and surprised by the many parallels between his life and Hasan's -- both have a Muslim heritage, both grew up in Virginia and both work with the military as a psychiatrist.
Yet, Afkhami said, "I don't think we should get lost on his identity."
Family and neighbors have told ABC News that Hasan was a pious Muslim and solitary man, but was outspoken about his views against the current wars in Iraq and Afghanistan.
"He's a quiet man, he looked like a nice person to me, so since I have been living here I never heard a noise in that house," said Vivian Tchangan, his former neighbor in Silver Spring, Md. Tchangan added that Hasan wrote "Allah" on his door.
Hasan relocated to Fort Hood in Texas and was soon to be deployed to Afghanistan, U.S. Army officials confirmed Friday. He is now in critical condition and paralyzed at a hospital in Texas after being shot multiple times by a police officer.
Hasan's former colleague, Retired Army Col. Terry Lee, told Fox News that Hasan frequently voiced his opposition to the wars in Afghanistan and Iraq and had hoped to avoid deployment.
However, his cousin Nader Hasan believes the upcoming deployment is what set him off. The cousin said the family was close -- "my mom is his mom" and yet "we didn't know he was being deployed until we heard it on the news today."
To some, an Internet message posted this spring under Hasan's name that argues suicide bombers are not committing murder but rather "to help save Muslims by killing enemy soldiers" is evidence enough that the shooting at Fort Hood was an act of terrorism.
"This man put out his thoughts on blogs on the War in Iraq, he equated the actions of a suicide bomber to a soldier who throws himself on a grenade to protect his troops," said Dr. Cyril Wecht, a lawyer and forensic psychiatrist at the University of Pittsburgh Medical Center. "When you correlate this with his beliefs societally and religiously and so on, to be hesitant and embarrassed to feel that you are identifying him as a Muslim acting out [for terrorist reasons] is pusillanimous and unrealistic and dangerous."
As of Friday morning, the Associated Press reports that U.S. officials have not ruled out the possibility that Hasan was planning his shooting spree or collaborating with a radical group or organization.
But if he was indeed acting alone, psychiatrist Dr. Steven Dinwiddie said among solo mass murderers, mental illness usually attracts and twists religious beliefs -- not the other way around.
"I think it would be a mistake for people to theorize [he did this] because he is an adherent of this or that religious faith," said Dinwiddie, a professor of psychiatry and behavioral neuroscience at the University of Chicago. "The mental illness comes first, then flowing from that is the adoption of perhaps, unusual, religious beliefs."
Afkhami also wondered if the public will place too much emphasis on Hasan's religion. Based on Afkhami's experience lecturing and working with the military, and plain common sense, it follows that few, if any, of those who oppose the war have turned to radical acts such as a shooting rampage.
"We're missing a core underlying issue, there are tons of religious folks who are morally opposed to the war on some level who are still serving in the military and get things done," said Afkhami.
Rather, Afkhami is convinced that a combination of stressors in Hasan's life -- especially in his role as a military psychiatrist -- could have led him to a breakdown.
"They have very large patient loads more and more veterans are coming back with psychiatric illnesses," said Afkhami, who works with the military as a lecturer in the Leader Development and Education for Sustained Peace program. "Out of all the medical doctors, psychiatrists are bearing the brunt of war casualties."
Afkhami guessed that adding the stress of hearing war stories from returned soldiers "to the mix of someone who has a feeling of being persecuted in the military because of his background -- whether he had a real perception or a false one -- and this imminent deployment," might be enough to turn someone with a psychiatric problem into a murder.
Ragan knows all too well that military psychiatrists can be under a lot of pressure and hear some horrible things. As a military psychiatrist at Camp LeJeune in North Carolina he and two other colleagues were assigned to 43,000 people.
"I was on call every third night for three years," said Ragan, adding that the long hours aren't the worst of it. Talking to soldiers who have Post Traumatic Stress Disorder (PTSD) from combat can be quite chilling.
"The horrors of war of what they told me over the years would curl the hair on a bald man's head," said Ragan, "although you should have the training to deal with this."
Ragan said that psychiatrists are well-trained to deal with such stressors in the military. Moreover, compared with some other situations in which psychiatrists are sent off to war with little notice, Hasan had years of training to prepare for a military setting.
"These things are stressful, but the training should be what gets people to a place to where people can cope with that. He had lots of training. And he was older," said Ragan. "I hate to think what it was like for physicians during WWII and you get three months."
Hasan, 39, got his medical training with the military at the Uniformed Services University of the Health Sciences in Bethesda, Md. He graduated in 2003 with a degree in osteopathy and later finished his residency as a psychiatrist. In 2009, Hasan completed a fellowship in disaster and preventive psychiatry at the Center for Traumatic Stress.
He was promoted to major in May, according to the Army Times.
"This is a guy who's been in a very protected secure environment and people are saying it's time for you to take your training wheels off and go," said Ragan. "I think the die was cast before he even arrived at Fort Hood."
ABC News' Emily Friedman, Brian Ross, Joseph Rhee, Anna Schecter, Avni Patel, Ethan Nelson, Desiree Adib, and Courtney Hutchison contributed to this report.