It was repulsive and disturbing enough when it was reported in January that U.S. soldiers had urinated on the dead bodies of suspected Taliban members and, more recently, had accidentally burned Korans.

Now, even more reprehensible, a U.S. soldier–and possibly more–went on a rampage, killing 16 people, including nine children and three women, on Sunday in Kandahar, Afghanistan.

The soldier, a staff sergeant, left his base and went from door to door on his killing spree, at some point gathering several bodies and setting them on fire.

President Barack Obama responded immediately to the incident. “I offer my condolences to the families and loved ones of those who lost their lives and to the people of Afghanistan, who have endured too much violence and suffering,” he said in a written statement.

“This incident,” he continued, “is tragic and shocking, and does not represent the exceptional character of our military and the respect that the United States has for the people of Afghanistan.”

Moreover, he said that a full investigation of the incident would begin immediately in order to obtain “the facts as quickly as possible and to hold accountable anyone responsible.”

There is much speculation over what might have triggered such a cold-blooded massacre. It was reported that the soldier was serving his fourth tour of duty in a combat zone and he may have cracked under the pressure.

Many soldiers in Afghanistan and Iraq have shown signs of breaking down, even taking their own lives. According to one report by the British journal Injury Prevention, Army suicides are up 80 percent since the U.S. began its occupation of Iraq.

“From 1977 to 2003,” the report said, “the tally of Army suicides had tended slightly downward and far below civilian rates, but it started to curve upward in 2004.”

Though the president has called for an investigation, it remains to be seen the extent to which the soldier will be punished. Only one of the nine soldiers charged in the massacre of 24 Iraqi men, women and children in Haditha in 2005 was convicted. That soldier, Staff Sgt. Frank Wuterich, who was charged with leading the slaughter, was convicted of “dereliction of duty” and demoted to private without serving time in jail.

In effect, there is nothing new about atrocities committed by U.S. soldiers, which goes all the way back to the Revolutionary War and certainly includes Vietnam and the incident at My Lai.

Reporter and author Jon Lee Anderson, in a recent issue of the New Yorker, put those soldiers’ misdeeds in historical perspective.

“Such incidents are not unfamiliar to Americans–or should not be,” Anderson wrote. “They happened in Iraq, too. There were the Abu Ghraib ignominies and the Haditha massacre, and there were a thousand lesser, sometimes unreported incidents in which soldiers humiliated, abused or killed Iraqi civilians for reasons that had less to do with the Iraqis’ possible hostile intentions and more to do with the Americans’ fears and hatreds.”

Meanwhile, Afghanistan President Hamid Karzai said the “assassination…cannot be forgiven.”