JOINT BASE LEWIS-McCHORD, Wash. -- As Army officials weigh whether a case against a staff sergeant accused of killing 16 Afghan villagers in a predawn rampage will proceed to a court-martial, Robert Bales' defence team says the government's case is incomplete.

And outside experts say a key issue going forward will be to determine whether Bales, who served tours of duty in Iraq and Afghanistan, suffered from post-traumatic stress disorder.

"There are a number of questions that have not been answered so far in this investigation," defence attorney Emma Scanlan told the investigating officer overseeing the preliminary hearing during closing arguments Tuesday.

Scanlan said that it's still unknown what Bales' state of mind was the evening of the killings. Prosecutors say Bales, 39, slipped away from his remote base at Camp Belambay in southern Afghanistan to attack two villages early on March 11. Among the dead were nine children.

An Army criminal investigations command special agent testified last week that Bales tested positive for steroids three days after the killings, and other soldiers testified that Bales had been drinking the evening of the massacre.

"We've heard that Sgt. Bales was lucid, coherent and responsive," Scanlan said in her closing argument. "We don't know what it means to be on alcohol, steroids and sleeping aids."

But prosecutors, in asking for a court-martial trial with the option of the death penalty, pointed to statements Bales made after he was apprehended, saying that they demonstrated "a clear memory of what he had done, and consciousness of wrong-doing."

Several soldiers testified that Bales returned to the base alone just before dawn, covered in blood, and that he made incriminating statements such as, "I thought I was doing the right thing."

The slayings drew such angry protests that the U.S. temporarily halted combat operations in Afghanistan, and it was three weeks before American investigators could reach the crime scenes.

"Terrible, terrible things happened," said prosecutor, Maj. Rob Stelle. "That is clear."

The investigating officer said Tuesday that he would have a written recommendation by the end of the week, but that is just the start of the process. That recommendation goes next to the brigade command, and the ultimate decision would be made by the three-star general on the base. There's no clear sense of how long that could take before a decision is reached on whether to proceed to a court-martial trial.

If a court-martial takes place, it will be held at Joint Base Lewis-McChord, the Washington state base south of Seattle, and witnesses would be flown in from Afghanistan.

Bales' wife, Kari, and her sister, Stephanie Tandberg, met with reporters briefly after the hearings concluded. Tandberg read a statement, saying "we all grieve deeply for the Afghani families who lost their loved ones on March 11, but we must all not rush to judgment."

The military hasn't executed a service member since 1961, and none of the six men on death row at Fort Leavenworth, Kan., today were convicted for atrocities against foreign civilians. All of their crimes involved the killing of U.S. civilians or fellow service members.

In the most recent high-profile case at Joint Base Lewis-McChord before Bales, the Army did not seek a death penalty court-martial against five soldiers accused of killing three Afghan civilians for sport. In that case, the ringleader was sentenced to life in prison with possibility of parole.

Bales faces 16 counts of premeditated murder and six counts of attempted murder. The preliminary hearing, which began Nov. 5, included nighttime sessions on Friday, Saturday and Sunday for the convenience of the Afghan witnesses. Bales did not testify.

Last week, the lead prosecutor, Lt. Col. Jay Morse, said on the night of the killings Bales watched a movie about a former CIA agent on a revenge killing spree, with two fellow soldiers, while drinking contraband whiskey. Morse said Bales first attacked one village, Alkozai, returned to the base at Camp Belambay, then headed out again to attack a second village, Najiban. Bales returned to the base covered in blood, Morse said, and his incriminating statements indicate he was "deliberate and methodical."

None of the Afghan witnesses were able to identify Bales as the shooter, but other evidence, including tests of the blood on his clothes, implicated him, according to testimony from a DNA expert.

After the hearing concluded, Scanlan spoke with reporters, saying that in addition to questions about Bales' state of mind, there are still questions of whether there were more people involved.

During testimony, a special agent testified that months after the killings, she was able to interview a victim's wife who recounted having seen two U.S. soldiers. Later, however, the woman's brother-in-law, Mullah Baraan, who was not present at the shootings, testified the woman says there was only one shooter. The woman herself did not testify.

"We need to know if more than one person was outside that wire," Scanlan said.

Scanlan also raised the issue of post-traumatic stress disorder and brain injury, noting that Bales had received a screening at the traumatic brain injury clinic at Madigan Army Medical Center during a period of time that the centre is under investigation for reversing hundreds of PTSD diagnoses of soldiers since 2007.

"We're in the process of investigating that," she said.

When asked if Bales had ever been diagnosed with PTSD, Scanlan said, "I'm not going to answer that right now."

Dan Conway, a military defence lawyer based in New Hampshire, said Tuesday that PTSD must be considered in the case.

"I think the defence team has an obligation to meet with doctors and determine if PTSD affected Bales' ability to premeditate the murders," Conway said.

Eric Zillmer, a military psychology expert at Drexel University in Philadelphia, said many people suffer from PTSD and still function just fine in society.

He noted Bales was considered fit for duty when the killings occurred, but he said PTSD could be a contributing factor to Bales' actions, which sets up a key issue to be decided.

"Is this a bad apple who should be punished?" Zillmer asked. "Or is he to some extent an actor who didn't have complete control over all his behaviors? I think it would be difficult to make PTSD completely responsible for the series of murders this perpetrator committed."