Horror in Kandahar - NYTimes.com The massacre of at least 16 civilians in three Afghan villages by an American soldier on Sunday was an unspeakable horror. The United States said Monday that an investigation is under way. It must be fast, transparent and conclusive so that Afghans can see that America is committed to justice and responsive to their outrage. The punishment must be swift. According to American and Afghan officials, the soldier shot the civilians execution-style, including nine children, after methodically breaking into three separate houses in a district of Kandahar Province. After killing the civilians, he set some of their bodies on fire. The soldier's name has not been disclosed, but, according to The Times, he is a 38-year-old Army staff sergeant and a married father of two children based at Joint Base Lewis-McChord near Tacoma, Wash. He had three tours in Iraq and was on his first tour in Afghanistan. This atrocity appears to be the act of one individual. No one has suggested a motive. But if the investigation reveals that the sergeant showed signs of mental illness or other forms of distress, then this tragedy clearly has significant implications for how the military identifies, monitors and treats troubled service members. The Pentagon needs to make that issue part of a thorough inquiry. Sunday's massacre is another dangerous setback for the United States as it tries to adhere to a plan for drawing down its forces in Afghanistan by the end of 2014 and reaching a peace agreement with the Taliban. This is the third recent incident to enrage Afghans and provoke ever more forceful demands that American troops leave immediately. Last month, American personnel inadvertently burned some Korans, and, in January, American Marines were shown on video urinating on the corpses of dead Taliban militants. Anti-American tensions are running so high that an agreement with Afghanistan now being negotiated to authorize the long-term stationing of American special operations forces could be in jeopardy. And there are growing concerns that any Americans, military or civilian, could be subject to retaliation. There are roughly 90,000 American troops in Afghanistan now, with 22,000 scheduled to leave by this fall. The Obama administration is now considering reducing troop levels in Afghanistan by at least 20,000 by 2013, and possibly even deeper, according to Helene Cooper and Eric Schmitt of The Times. The United States has a vital interest in ensuring Afghanistan doesn't again become a launching pad for terrorist attacks. It has to keep moving forward with negotiations on an American presence after 2014, while continuing to review whether there are prudent ways to speed the process for withdrawal.