Five U.S. soldiers stand accused of using grenades and rifles to murder three unarmed Afghan civilians earlier this year, and investigators say several of the soldiers even collected the dead civilians' body parts.
In a videotape obtained by ABC News' Brian Ross Unit, one of the accused soldiers, Cpl. Jeremy Morlock, confessed to the murders. He said the officer in charge, Sgt. Calvin Gibbs, gave orders to carry out the killings and that Gibbs had no problem murdering innocent civilians.
Mental health experts overwhelmingly agreed the actions the soldiers have been accused of are inexcusable, and they said a number of complex psychological factors may play a role in why soldiers obey their commander's orders -- even when this means committing atrocities. The emotional toll of combat, people's tendency to do whatever they're told to do and the soldiers' fear of their sergeant, whom several of the them portrayed as a "thrill killer," could have contributed to their decision to kill unarmed civilians, they said.
"Sleep deprivation plays a role, there's some question of traumatic brain injury and some question about the use of prescription drugs," said Dr. Jon Shaw, a professor of psychiatry at the University of Miami School of Medicine who spent more than 20 years in the military. He has no involvement with the accused soldiers.
The attorney for one of the accused soldiers said his client was under the influence of prescription drugs during his videotaped confession. Another of the accused soldiers said drug use -- often hashish laced with opium -- was rampant at their base in Afghanistan.
"There's a serious problem with substance abuse happening among our soldiers," said Dr. Jeffrey Victoroff, associate professor of clinical neurology and psychiatry at teh University of Southern California's Keck School of Medicine. He added, though, the he doesn't believe substance abuse alone led to murder.
Extreme stress, psychiatrists say, is perhaps one of the biggest factors that can affect soldiers' judgment.
"When you're exposed to that kind of stress, there's a readiness to be more passive and accept external authority, especially in a command structure," Shaw said.
"This is a very prolonged conflict and engagement, and there are multiple indications that these army units are worn out," said Dr. Paul Ragan, associate professor of psychiatry at Vanderbilt University Medical Center. Ragan, who served in Operation Desert Storm in the early 1990s, has no involvement with the soldiers.
Ragan said that in a war that's lasted nearly a decade, soldiers in combat could experience a wide range of emotions that influence their behavior.
"They may be suffering from mental fatigue, or may be feeling dispossessed and angry," Ragan said. "Are these men put in impossible situations [in which they] begin to dehumanize the other group and take their rage out on innocents?"
The emotional upheaval may also affect their moral judgment.
"In a group, there's regression to the lowest level of morality," Shaw said.
The parents of another accused soldier, specialist Adam Winfield, said their son felt his life would be in danger if he reported Gibbs.