JOINT BASE LEWIS-MCCHORD, Wash. -- Two unarmed Iraqi brothers posed no threat as they herded cattle in a palm grove where a U.S. Army reconnaissance team was hidden one day seven years ago, a former soldier said Wednesday at a preliminary hearing.

But then-Staff Sgt. Michael Barbera took a knee, levelled his rifle and killed them -- from nearly 200 yards away, former Spc. John Lotempio testified.

"Oh my God -- why?" he said when a prosecutor asked him to describe his reaction to the killings. "They didn't see us."

Barbera, 31, now a sergeant first-class, faces a mandatory sentence of life in prison if convicted of premeditated murder in a case that raised concerns about a possible coverup. Two years after the killings, Army criminal investigators looked into the case, but commanders decided to give Barbera a letter of reprimand instead of a court martial.

It was only after a Pittsburgh newspaper, The Tribune-Review, published an investigation about the matter in 2012 that the Army took another look. The story described how some of Barbera's fellow soldiers remained troubled that he was never prosecuted, and it prompted calls from Congress for the Army to review the matter.

As the hearing began Wednesday at Joint Base Lewis-McChord, south of Seattle, Barbera's attorney, David Coombs, called the allegations baseless and highlighted the lingering questions about why it has taken so long to bring the case to court. An investigating officer, Lt. Col. Charles N. Floyd, is considering whether Barbera should face a court martial.

Coombs alleged that the newspaper's "hit piece," which won an investigative reporting award, and congressional pressure had improperly influenced the Army's decision to file charges against Barbera last fall.

Barbera's fellow soldiers didn't begin to come forward to report concerns about the shooting until 2009, and a criminal investigation was conducted then. The matter was "somehow put to bed by administrative action," Capt. Ben Hillner, an Army prosecutor, said in his opening statement.

Hillner did not elaborate on that decision by commanders at Fort Bragg, North Carolina, where Barbera was then based.

Lotempio, who said he witnessed the shootings, said he didn't report them at the time because "I don't think I knew the proper way to go about it. I didn't want to think about it." He has suffered from nightmares about the killings, he said, and he felt guilty because he was the one who first noticed the boys and woke up Barbera, who promptly shot them.

"If I didn't wake him up, they'd still be alive," he said.

He said "absolutely not" when asked if the boys posed a threat: "They looked to be about 10 or 11."

Even if the boys were acting as scouts for Iraqi fighters, they couldn't have seen the soldiers, especially from such a great distance, because they were behind a log and thoroughly covered with tall grass, Lotempio said.

After Barbera killed the first boy with a single shot to the head, the second waved to them with one hand and yelled, "Hello, mister! Hello!" Lotempio said. Barbera fired a second shot that killed him.

Lotempio said the shootings contravened the rules of engagement for the mission, which was not to fight unless the enemy had the means, opportunity and intent to cause harm.

Coombs, who represented Chelsea Manning, the Army private convicted of leaking a massive trove of information to Wikileaks, argued in his opening statement that even though the soldiers' rules of engagement required them to report violations, it was two years before any raised concerns.

Further, he said, the reporter who wrote the stories, a former Marine named Carl Prine, was too ready to believe what Barbera's former comrades told him.

Prine was called as a witness Wednesday to testify about an allegation that Barbera threatened his wife in 2011, saying words to the effect of: "For your own personal safety, you need to tell your husband to back off the story," Hillner said Wednesday.

That's the basis of another charge against Barbera, conduct prejudicial to good order and discipline. He's also accused of trying to get a soldier in 2009 to tell investigators that the dead boys might have been wearing suicide vests.

Prine told the investigating officer that he did not expect his newspaper would be willing to turn over videotapes of interviews conducted for the story, in particular interviews of the boys' relatives he conducted in Iraq.

The shootings were near the village of As Sadah, in Diyala Province. Barbera was the leader of an eight-man reconnaissance team that had planned to remain secreted in the grove for two to three days monitoring possible enemy activity.

After the brothers were killed, Barbera's group also killed their cousin, who approached the scene along a footpath. No charges were filed in that shooting. The first witness to testify Wednesday, former Army medic Andrew Harriman, fired the shot that killed the cousin and said it appeared the man had been reaching for a weapon.

Contrary to Lotempio's story, Harriman testified that Barbera fired five or six shots at the boys. Harriman didn't see where Barbera was shooting, and he said he only learned after the fact from another soldier, Pfc. Dary Fink, that Barbera had killed two unarmed boys.

Harriman said he believed he urged Fink to report the shootings. Nevertheless, Harriman also testified that he believed his immediate commanders would have swept the matter under the rug.

The victims were identified as Ahmad Khalid al-Timmimi, 15; his brother Abbas, 14; and their cousin, Muhamed Khaleel Kareem al-Galyani.