Elite US unit in Afghanistan concealed abuse, killing of detainees

The Jurist, citing the LA Times: "A US Special Forces team in Afghanistan allegedly abused and killed two detainees in their custody and then coordinated their stories so that superior officers in the chain of command never discovered the incidents."

Is it fair to wonder how often stuff like this happens, whether it be in Iraq, Afghanistan, or elsewhere? More to the point, how often this stuff happens with no alarm or investigation?