Complex sentence: Visser orders everyone out and announces that Hart will be shot there and then, but before the sentence is carried out, McNamara moved by this selfless sacrifice, voluntarily returns to the camp to accept responsibility.
Split into simpler sentences: Visser orders everyone out and announces that Hart will be shot there and then. But before the sentence is carried out McNamara, moved by Hart's selfless sacrifice, voluntarily returns to the camp to accept responsibility.