James Lives on the Southern Border of Texas

James lives on the southern border of Texas. He can see Mexico from his home. He has grown tired of watching people come across the border illegally and has decided to do something about it. He joins a local vigilante group that works to contain illegal immigrants by whatever means necessary and return them to Mexico. During one capture thing got out of hand and he fatally shot a Mexican citizen. If James' defense is that he was acting as a lawful combatant, will he be successful?

A) Yes
B) No, unless he was wearing camouflage at the time of the incident
C) No, because he was not acting in concert with a recognized armed force
D) Yes, because he was working on behalf of the United States