This rather serious report should be of interest to LW. It argues that autonomous robotic weapons which can kill a human without an explicit command from a human operator ("Human-Out-Of-The-Loop" weapons) should be banned, at an international level.
(http://www.hrw.org/reports/2012/11/19/losing-humanity-0)
It's unlikely that a human would actually do this. They would have been trained to react quickly and to not take risk / chances with the lives of their fellow soldiers. Reports from Cold War era wars support this view. The ( possibly unreliable ) local reports in current war torn regions also support humans not making these distinctions, or at least not making them when things are happening quickly.