Here is an interesting thought.
Apostacy in Islam, i.e., 'the public declaration of rejecting the fundamentals of Islam' is tantamount to treason and is treated very seriously indeed. I understand that the punishment prescribed by the shari'a for apostacy is death.
Now, if a person were to carry out acts which were so fundamentally against the grain of Islamic tenets (such as sawing off a man's head whilst chanting 'God is Great') is there an argument that this person has has so publicly rejected the fundamentals of Islam, that he should be put to death by his own community as an apostate?
You could argue that by carrying out the act, this person has renounced Islam.
I don't know if this argument flies in the corridors of mosques amongst the learned there, but if it does, it would be a very good way to use Islam to prevent such deeds from happening again. All it would take are some respected religious leaders to make this view publicly known.
Ravs