(CBS News) WASHINGTON -- The number one question is motive: Why did an American Army sergeant walk into an Afghan village and kill 16 civilians?
What appeared to be a cold-blooded shooting rampage drew a harsh reaction from Afghan President Hamid Karzai. He labeled it an "assassination" and demanded justice.
President Obama, on damage control, talked with Karzai on the phone and promised to investigate. In a statement, Mr. Obama called the killings "tragic" and "shocking." He also tried to paint it as an isolated incident -- saying the attack "does not represent the exceptional character of our military."
Defense Secretary Leon Panetta said he was "saddened that a U.S. service member is ... involved."
Military investigators in Afghanistan have been questioning the suspect, who is based at Joint Base Lewis-McChord, near Tacoma, Wash.
This was his first tour in Afghanistan, but he had served several times in Iraq.
He's 38, and married with two children. Sources say his name will be released when he is charged.
He was part of what's called a village stabilization program in Afghanistan, in which troops work to develop close ties with village leaders.
Joint Base Lewis McChord has a history with troubled soldiers.
It's where Staff Sgt. Calvin Gibbs was recently convicted of killing Afghan civilians for sport. It's where Benjamin Colton Barnes was stationed. Barnes, an Iraq War veteran, was suspected of killing at Mount Ranier National Park ranger on New Year's Day. Barnes' body was later found in the park. The "Beltway Sniper," John Allen Muhammad, was also stationed at Joint Base Lewis-McChord. He was executed in 2009 for killing 10 people around Washington, D.C.
And just recently, the base's chief medical administrator was suspended because of problems with screening and treating post traumatic stress disorder.
As of Sunday night, the Army was still trying to locate the sergeant's family to tell them what had happened, and they are worried about the family's security.
As for the probe, you have to have forensics to make an ironclad case in court. So investigators will be doing that on the scene, doing autopsies on the bodies and recovering the bullets to match with the gun that was used.
They also have to look into the suspect's background. This guy had a number of tours in Iraq, and now, of course, the tour in Afghanistan. And the question is -- was he suffering from Post Traumatic Stress Disorder.
To see David Martin's report, click on the video in the player above. For a look at the possible impact of the incident on U.S.-Afghan relations, click on the video below of a discussion between "CBS This Morning" co-host Charlie Rose and CBS News consultant Jere van Dyk: