The lawyer for a 38-year-old U.S. serviceman accused of killing 16 Afghan civilians has disputed a number of theories floated to explain the actions of the staff sergeant, who was being flown to Fort Leavenworth, Kansas, on Friday to stand trial. Efforts to characterize the unidentified soldier's alleged crimes on March 11 include a New York Times article indicating that he simply "snapped" prior to the shooting due to the stresses of combat, marital problems or drinking too much alcohol.

The soldier—who enlisted in the military a week after the September 11, 2001, attacks and had served three tours in Iraq—has suffered several combat-related injuries, including a concussion sustained by a roadside bomb and the loss of part of a foot, his attorney John Henry Browne acknowledged. The lawyer did not speculate as to whether his client might have psychological or mental health problems. But Browne did tell CNN that during a brief phone conversation with the soldier, "he seemed to be unaware of some of the facts I talked to him about, which makes me concerned about his state of mind."

Even if the soldier's state of mind is unknown at this time, the nature of his previous injuries may provide some insight into the forces at work on him. Blunt-force trauma, which can be caused by concussion-inducing trauma, damages the brain by bruising it, stretching or tearing nerve cells, or triggering electrical misfiring, Scientific American Mind reported in its December 2008 issue. In addition, an incident strong enough to cause traumatic brain injury can also be powerful enough to produce emotional trauma and post-traumatic stress disorder (PTSD). A combination of mild traumatic brain injury and PTSD is considered the signature injury of the Iraq War.

A 2010 study of more than 18,000 U.S. Army soldiers returning from combat in Iraq found up to 31 percent reported symptoms of PTSD or depression as long as a year after returning from the battlefield. About half of soldiers who had PTSD or depression also reported aggressive behavior or misuse of alcohol. PTSD diagnoses themselves have become controversial, however, with critics pointing out that criteria for assessing PTSD are based on a "faulty, outdated construct that has been badly overstretched" and that many soldiers are misdiagnosed as having the disorder.

As to whether the soldier accused of the recent massacre in Afghanistan's Kandahar Province simply lost cognitive control—or snapped—following one or a series of stressful situations, researchers note that individuals respond to stresses in different ways. A variety of issues can lead a person to a lose their ability to "exercise cognitive control in a healthy manner," Marco Iacoboni, a University of California, Los Angeles, professor of psychiatry and biobehavioral sciences and director of the school's Transcranial Magnetic Stimulation Laboratory, told Scientific American last year after the Gabrielle Giffords shooting.

In such cases, the person's self-control mechanisms are redirected toward goals and activities that are violent in a very specific way. "The violence is channeled in a very specific plan, with a very specific target—generally fed by the media through some sort of rhetoric, political or otherwise—with very specific tools," Iacoboni said.

For the Army sergeant at the center of the shootings, that plan allegedly included hiking more than a mile to a rural Afghan village and going on a shooting spree that left nine children dead. It may be a long time, if ever, before we truly understand the shooter's state of mind.

Image of U.S. soldiers in Afghanistan courtesy of Craig DeBourbon, via