A US soldier charged with slaying 16 civilians, most of them women and children, near his Army post in Afghanistan was diagnosed before his deployment as suffering from post-traumatic stress disorder and a brain injury, his lawyer said.
Prosecutors are seeking the death penalty against Robert Bales, a decorated veteran of four combat tours in Iraq and Afghanistan who is accused of gunning down the villagers in cold blood during two rampages through their family compounds in Kandahar province last March.
Military justice experts say the post-traumatic stress disorder (PTSD) diagnosis, if substantiated, may prove of limited value in helping Bales' attorneys pursue an insanity defence but could make it more difficult for prosecutors to obtain the death penalty, even if they can prove premeditation.
The disclosure that Bales had been diagnosed with PTSD followed a hearing in which defence lawyers told a military judge they were preparing a possible ''mental health defence'' for Bales, who appeared in court wearing a green military dress uniform.
The judge, Colonel Jeffery Nance, said such a defence would require a formal psychiatric evaluation and that he would order a ''sanity board'' of independent doctors to review Bales' mental condition.
During Thursday's 90-minute hearing at Joint Base Lewis-McChord near Tacoma, where Bales is being held, defence lawyers also deferred entering a plea on behalf of their client and waived a formal reading of the charges against him.
Asked by the judge whether he understood that the case against him could result in the death penalty, Bales, 39, an Army staff sergeant, replied, ''Sir, yes sir.''
Under the military justice system, a plea is commonly postponed at this stage to preserve legal options for the defence, whose ability to make additional motions is severely restricted once a plea is entered, experts say.
Civilian defence lawyer John Henry Browne told the judge that Bales' legal team would need at least a year and a half to prepare its case.
Prosecutors say Bales, a father of two from Lake Tapps, Washington, acted alone and with ''chilling premeditation'' when, armed with a pistol, a rifle and a grenade launcher, he left his base twice, returning in the middle of his rampage to tell a fellow soldier: ''I just shot up some people.''
The shootings, which occurred over a five-hour period in March, marked one of the deadliest incidents the military has blamed on a rogue US soldier since the Vietnam War, and strained US-Afghan relations.
BRAIN INJURY DIAGNOSIS
Browne said he had government documentation showing that personnel at Lewis-McChord's Madigan Medical Centre had found his client to be suffering from both post-traumatic stress disorder and a traumatic brain injury.
He said the diagnosis was made before Bales was deployed in November 2011 to Afghanistan on a tour of duty that ended abruptly with the events for which he is charged.
Defence lawyers have previously said that Bales, who faces 16 first-degree murder charges among other offenses, had suffered a possible concussion from a bomb blast during a prior tour of duty in Iraq.
Legal experts said evidence of PTSD or a brain injury might be used by the defence to bolster an insanity claim, but they doubted such a diagnosis could convince jurors that the accused was unable to appreciate the nature and consequences of his actions - the definition of insanity under military law.
''My research has not revealed a single case in which any person mounted a successful insanity defence in a court-martial based on a PTSD claim,'' said Eugene Fidell, who teaches military justice at Yale Law School.
But the defence could argue that Bales' PTSD and brain injury were severe enough to cause ''diminished mental capacity,'' making it harder for prosecutors to prove premeditation, which is necessary for him to be eligible for capital punishment, experts said.
Even if the jury finds Bales guilty of premeditated murder, a PTSD claim might be enough to sway just one member of the panel to vote against the death penalty during the sentencing phase of the court-martial. The panel must be unanimous in approving the death sentence.
''That's probably where this evidence would be the strongest and have the most impact on a capital case,'' said Victor Hansen, a former Army attorney who is now vice president of the National Institute of Military Justice and a professor at the New England School of Law in Boston.
Experts doubted that jurors, all members of the military themselves, would be sympathetic to an overt argument that the military was to blame for deploying a soldier suffering from post-traumatic stress disorder.
Defence attorney Emma Scanlan said Bales would participate in a review of his mental state, but wanted him to be examined by a neuropsychologist with expertise in traumatic brain injuries. She also wanted defence attorneys to be present at the examination, which the defence wants recorded.