Whether it was a psychotic break or underlying mental illness that led a United States Army soldier to allegedly massacre 16 Afghan civilians -- including women and children -- is still unclear.
But as military investigators reportedly interrogate the 38-year-old staff sergeant they say they believe to be behind the Sunday morning killing spree, psychological experts said such actions are generally preceded by strong signals that something is wrong -- signals that, in this case, may have been missed or gone unreported.
The soldier, whose name has not been released, is believed to have returned to the base of his own volition after the killings and have turned himself in. According to military statements, investigators have the soldier in custody and are trying to learn more about what happened -- and what may have precipitated the incident.
All of the mental health experts contacted by ABC News said that until more information is made available they could only speculate as to exactly what happened. But most said that warning signs generally presage violent actions like this one.
"This could have been signaled by erratic and changed behavior in the soldier including strange or unusual behavior, insomnia, weight loss, talking nonsensically or incoherently, making threatening statements and using drugs," said Dr. Jeffrey Lieberman, chairman of psychiatry at the Columbia University College of Physicians and Surgeons and director of the New York State Psychiatric Institute, in an email. "Rarely do such incidents of extreme behavior occur without some preceding signs."
"The individuals responsible for mass murders similar to this in the United States... have often given off strong signals of serious mental illness to friends, parents, associates, etc. prior to the incident," said Dr. Paul Newhouse, director of the Center for Cognitive Medicine at Vanderbilt University School of Medicine in Nashville, Tenn. and a former lieutenant colonel in the U.S. Army Medical Corps, in an email. "If this individual was seriously mentally ill, then it is possible that he may have showed signs of this type of disturbance to fellow soldiers and NCOs or medical personnel."
Dr. Simon Rego, director of psychology training at Montefiore Medical Center in New York, said in an email that warning signs "are not always obvious," but he noted that some of the more well-known ones -- such as "difficulty regulating emotions, discipline problems, getting into fights, withdrawal from others, damaging/destroying property [and] increasing risk-taking behavior" may be observed before an act of extreme violence.
Whether any of these warning signs were present before the alleged mass killing is as yet unknown. But Dr. Bengt Arnetz, professor of occupational and environmental medicine at Wayne State University in Detroit, Mich., said that even if these signals were present, the current system used by the military is woefully inadequate at detecting them.
"All the systems have never been evaluated," said Arnetz, whose research focuses on the effects of stress on the psychological well being of police, first responders and soldiers. "I think that they're very, very bad at monitoring people close to the breaking point. We don't have good surveillance tools."
As for the nature of the problem, Arnetz drew an analogy between the maintenance and monitoring of military machinery and the maintenance and monitoring of soldiers' mental states. "If you look at the machinery, you check for wear and tear and you do repair work and tune it up on regular basis," he said. "We're much worse with that approach with soldiers... We don't have that approach to it where soldiers are concerned; we don't have a systematic approach."
Worse, Arnetz said that even if troubling signs are apparent, some soldiers may be hesitant to report unusual behavior on the part of their fellow troops.
"We have talked with police working in inner city Detroit, and they told me it's very difficult to bring it up," he said. "Sometimes when you bring it up... you see a behavior change, they either deny it or become quite aggressive. They don't want to push it."
Why Did Massacre Happen?
Even more of a mystery than what happened preceding the incident may be why it happened at all. Newhouse said that even though the alleged killing spree comes on the heels of the killings of two U.S. soldiers after a wave of anger sparked by the burning of several Korans by the U.S. military, these events are "unlikely to have been causative" of the massacre.
Lieberman speculated that one of three types of psychological situations could have led to the rampage: a psychotic break, an accumulation of resentment and anger, or simple sadism.
In a psychotic break, Lieberman said, the soldier would have experienced the onset of a psychotic disorder, such as schizophrenia, affective psychosis or stress induced psychosis. "This could have led him to carry out actions that seem irrational and don't make sense," he said. "Such an incident recently occurred with Jason Loughner in Arizona."
Lieberman said a buildup of resentment could have also led to the soldier's alleged unprovoked actions. "He could have endured the loss of friends and colleagues in the context of his service in Afghanistan," he said. "This anger and resentment could have led him to redress these losses and abuses in an impulsive act of violence. This seemed to have been the scenario of Lt. William Calley at My Lai Massacre in Viet Nam."
The third scenario, Lieberman said, is that the soldier is "a sociopath who [is] severely sadistic. If so he might have lacked any moral structure and acted to satisfy his feelings without ethical or moral constraint and feeling for human decency. This seems to have been the case with Charles Graner at Abu Ghraib."
Whether any one of these scenarios -- or something different altogether -- most accurately represents what happened near Kandahar on Sunday remains to be determined. Until then, Newhouse said, it will be impossible to reach a solid conclusion.
"The last comment I would make is a similar comment to the one that I made to the press after the Major Hassan incident at Fort Hood, namely that it is unwise to make general conclusions from extraordinary events," Newhouse said. "Thus I would suggest that people do not rush to judgment regarding the causes of this incident until further is known about the individuals mental state."