"he exhausted himself trying to prove his innocence" This is the correct option.
Hauchercorne, the character of "The Piece of String " by Guy de Maupassant (XIX), wanted to prove his innocence in front of the villagers. He died believing that noone would believe in an old crafty peasant as he was. People made fun of him whenever he told them he was innocent. He spoke in front of the villagers a lot of times. He had been falsely accused of stealing a man's pocketbook and some money.