What's a word that means to betray a religious group?

What's a word out of the dictionary that means to betray. I'm not looking for the word "traitor" either. It falls somewhere to the same category of words meaning pagan, heretic, and zealot. Even though those words mean the opposite. Something that means betrayer of faith, group, persons, or associated groups of what you once followed. But now you don't because you turned against your former belief. What would the enemy call you?