As far as I know, the only connection of him to the 4 is he went missing the same day.
Too much co-incidence, I would tie him down on an anthill and cover him in honey to let him slowly suffer to get it all out of him.
Just to clarify, I'm almost postive I read that the report that he was missing was filed the same day the 4 Marines were killed but he actually went missing about two days before. That, to my mind, makes it even more likely he may have had some involvement.