They have to do this. You cannot give blanket amnesty/approval for actions like this. At a minimum, you put the kid under the wringer to make it absolutely clear that shooting wounded people is not policy. That being said, there may be extenuating circumstances that let the kid off. But the Corps must make a statement that actions like this are not acceptible, at least on their face.
My bet is that they will find that the kid had less than 12 hours of sleep over a five day period...and was mostly mentally exhausted. For years, this scenario has been played over and over...and people (even pilots) can't operate at realistic mental capacity with a average of 3 hours or less of sleep per day. Take a stripe away from the kid....sent him to mental eval...and then welcome him back after six months. He's a great lesson upon other members of the corps on what can happen when you aren't thinking. He should not get jail time...its simply a total waste.