I met a New Zealander a few years back who was a US Marine. He claimed that the US military recruited English-speaking non-citizens to get around Posse Comitatus. He claimed to have been involved in all sorts of domestic shenanigans.
There are a lot of possibilities there, none of them good.
If he was a active duty US Marine, he could be from Mars, he is still bound to obey any laws that any other Marine has to abide by.