Thursday's deadly rampage raises a red flag over the issue of combat stress.

The suspected gunman, Major Nidal Malik Hasan, worked on that very issue at the Center for the Study of Traumatic Stress (CSTS), which assesses the behavioral and psychological risks of traumatic events, such as combat, terrorism, natural disasters and public health threats.

The most common disorder linked to combat stress is post-traumatic stress disorder (PTSD), which can develop after exposure to one or more traumatic events that threatened or caused great physical harm.

In this case, however, the suspect has not been in combat but instead was facing deployment into a combat zone.

Having counseled returning soldiers with PTSD, first at Walter Reed Army Medical Center in Washington and more recently at Fort Hood, Hasan knew all too well the terrifying realities of war, his cousin Nader Hasan told the New York Times.