What Sites fails to mention in this letter is that it is likely that the insurgent (terrorist) "peeping from his blanket" wasn't considered a threat because he wasn't feigning death (he was clearly alive, as were the other two near him). The other one, however, was perceived to be faking death, setting an alarm off in that Marine's head. Just today, Insurgents faking dead fires on Marines. There is good reason the Marine felt threatened by this man an not by the others clearly showing life signs.
FWIW - I believe that faking death is also against the Geneva Convention.