Earlier quoted context omitted.
Actually, the question was not whether Sutcliffe was justified in committing rape, but whether he was justified in believing that he was doing the will of God. If "firm inner conviction" justifies a belief, and Sutcliffe had firm inner conviction, then Sutcliffe was justified in his belief.
Well, it's a bit like this: 1. Is it justifiable to walk into a shop? 2. John Does walked into a shop and murdered all present. Was he justified in walking into the shop? Answering yes to 1 and no to 2 is a contradiction in the same way. But, is it really valid to separate the action of walking into the shop with the murder of those present? Is it really valid to separate Sutcliffe's belief from his actions?
1. Is it justifiable to speak freely?
2. John Doe announced that a crowded theatre was afire, and people died in a resulting stampede. Was he justified in speaking?
Nobody ever addresses the separability issue you describe.