U.S. Army and Afghan troops stand watch in a guard tower at their base in Panjwai, Afghanistan, in Kandahar province, on Sunday, March 11, 2012, after a U.S. Army sergeant allegedly killed 16 Afghan civilians in nearby villages. (AP Photo/Allauddin Khan)

Photo by: Allauddin Khan

U.S. Army and Afghan troops stand watch in a guard tower at their base in Panjwai, Afghanistan, in Kandahar province, on Sunday, March 11, 2012, after a U.S. Army sergeant allegedly killed 16 Afghan civilians in nearby villages. (AP Photo/Allauddin Khan)