Slaughter Trail (movie, 1951)

Three outlaws rob the stage and then flee. When their horses give out they murder some Indians to get fresh ones. But this puts the Indians on the war path and they have to take refuge in an Army fort to avoid them. The Indians then arrive offering peace if the three men are turned over to them. The fort's commanding Officer wants peace but the rules say the men must be tried in a white man's court leaving the Indians no choice but to attack.