Big difference.
So McVeigh and other terrorists who professed to be Christian were acting AGAINST the tenets of their faith, whilst John Taliban and the Washington sniper were in ACCORD with theirs.
The fact that most Muslims do not do likewise may mean they realize just how wrong it is to murder peaceful people simply for worshipping a different God. The fact that leaving the Muslim religion calls for an automatic death sentence should be clear evidence of its inherent wrongness.