A U.S. military investigation into an Army sergeant's shooting rampage in Afghanistan concludes that there were advance warnings that he was capable of unwarranted violence, but not that he would commit a large-scale atrocity like the slaughtering of 16 Afghan civilians, including seven children.

U.S. Central Command released a report Tuesday into the March 11, 2012 shootings by former Staff Sgt. Robert Bales.

It cited several incidents suggesting the potential for violent behavior by Bales, including an episode one month before the killings in which Bales punched and kneed an Afghan truck driver in front of other U.S. soldiers. A fellow soldier also expressed concern that Bales acted erratically while on steroids just before the killings.

Bales, previously assigned to Fort Lewis in Washington state, is serving a life sentence.