Which is why, when you are accused of criminal behavior, you really shouldn't say anything.
I'm not sure how lenient they should be, considering what MIGHT have happened instead.
The critical event--the point where this could've been prevented from happening--appears to be the decision to uncuff the prisoners. The USMC is unlikely to be lenient, because the USMC's policy is that if Person A gets killed due to Person B's breach of orders, then Person B is going to hang, particularly if he is in a leadership billet. It's the only way you can run a military, really. There may be an element of Voltaire's pour encourger l'autres at work, but it's just the nature of the beast.
I feel for him, though. Hindsight is always 20/20.
Well, he's prior enlisted, so he doesn't have the "I'm just a dumb 2nd Lieutenant with no experience whatsoever" excuse.