I would blame radical Judaism for many deaths going back to 1947, but thats just my opinion and can be discounted. Radical Catholicism has been a bane on Northern Ireland for most of the 20th century. Radical Hinduism has led to the deaths of many innocent Muslims in India. Any religion can be used to justify murder and death.
Many, many Islamic clerics deplored the 9/11 attacks, as did most leaders of Islamic countries (except Saddam, and well, what do you expect?). Hell, even _Qaddafi_ condemned the 9/11 attacks!
Go here for some genuine Muslim reactions to 9/11, from across the Islamic world:
http://www.unc.edu/~kurzman/terror.htm]