Army prosecutors on Tuesday asked an investigative officer to recommend a death penalty court martial for a U.S. soldier accused of killing 16 Afghan villagers in a pre-dawn rampage, saying that Staff Sgt. Robert Bales committed "heinous and despicable crimes."

Bales, a father of two from Lake Tapps, Wash., could face the death penalty. The military last executed a service member in 1961, when an army ammunition handler was hanged for raping an 11-year-old girl in Austria.

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In this courtroom sketch, U.S. army Staff Sgt. Robert Bales, seated lower right, watches witness testimony Friday. (Lois Silver/Associated Press)

Prosecutors made their closing arguments after a week of testimony in the preliminary hearing, known as an Article 32. Prosecutors say Bales, 39, slipped away from his remote base at Camp Belambay to attack two villages early on March 11. The 16-person death toll included nine children.

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 Maj. Rob Stelle, the prosecutor who delivered closing arguments in the preliminary hearing. "That is clear."

Stelle cited statements Bales made after he was apprehended, saying that they demonstrated "a clear memory of what he had done, and consciousness of wrongdoing."

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."

Case tests military justice system

The U.S. military justice system's record has shown it is slow to convict service members of alleged war crimes.

A range of factors make prosecuting troops for civilian deaths in foreign lands difficult, including gathering eyewitness testimony and collecting evidence at a crime scene in the midst of a war.

At Bales' preliminary hearing, the prosecution accommodated the Afghan witnesses by questioning them via a video link and holding the sessions at night. The military said it intends to fly the witnesses from Afghanistan if there is a court martial.

"I think it shows they're going to prosecute this case no matter what it takes," said Greg Rinckey, a former U.S. Army lawyer.

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An attorney for Bales argued there's not enough information to move forward with the court martial. "There are a number of questions that have not been answered so far in this investigation," attorney Emma Scanlan told the investigating officer overseeing the preliminary hearing.

Scanlan said it's still unknown what Bales' state of mind was the evening of the killings.

An army criminal investigations specialist had 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."

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.

Afghan witnesses testified at hearing

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.

The witnesses included a seven-year-old girl, who described how she hid behind her father when a gunman came to their village that night, how the stranger fired, and how her father died, cursing in pain and anger.

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.

Bales did not testify.

PTSD, brain injury concerns

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Kari Bales, left, listens as her sister, Stephanie Tandberg, right, reads a statement Tuesday to reporters after the preliminary hearing for Kari's husband, Staff Sgt. Robert Bales. (Ted S. Warren/Associated Press)

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 the wife of one of the victims, 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 that 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 center 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."

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."

"We are not convinced the government has shown us the truth, the whole truth, and nothing but the truth about what happened that night," added Tandberg. "We know Bob as bright, courageous and honorable, as a man who is a good citizen soldier, son, husband, father, uncle and sibling. We and Bob's family are proud to stand by him."