This is from 'Red Cross-The Law of Armed Conflict: Belligerent Occupation':

MILITARY COURTS/TRIBUNALS Although again in principle criminal offences in the occupied territory should continue to be prosecuted by the local courts, jurisdiction could pass, for example, to military courts of the occupying power if the local courts are not able to function properly. Any breaches of the penal provisions promulgated by the occupying power for its security may be prosecuted by its own military courts. Civilians who take a direct part in hostilities against the occupying power may be prosecuted. Remnants of the occupied country’s armed forces who continue fighting are of course combatants and must be treated as such. If captured, they are entitled to POW status and treatment as laid down in the Third Geneva Convention. In particular, they cannot be tried for the simple fact of taking part in hostilities. If, however, they commit acts in violation of the law of armed conflict, they may be subject to prosecution. Jurisdiction in penal matters may be assigned either to existing military tribunals or to special military courts created for the occupied territory, the judges being members of the occupying power’s armed forces. The courts must be non-political and properly constituted, the judges independent and impartial. Special courts set up on an ad hoc basis are not permitted. The courts must sit in the occupied country, i.e. the accused must be tried in their own surroundings. The occupying authorities may provide for or establish an appeal body, but are not obliged to do so. If they do not, convicted persons must at least have the right to petition. Again, courts of appeal so established should sit in the occupied country