Actually there are several verses of the القرآن الكريم (Qu'ran)that detail killing non believers/Pagans (infidels), 'seek them out and slay them wherever you catch them' (shortened version) - However I strongly believe a small cross section of muslims who are ignorant/uneducated in the proper context of the verses have taken this quite literally in modern day times, what they don't consider is that the book was written a long time ago and much of this content is based on rules of engagement in war when pagans were ripping through muslim villages, burning down peoples houses and raping women and killing children, equally the old testament also has verses of bestowing violence on non believers. It should also be noted that the same verses also advise of housing and granting asylum to pagans who repent - a prisoners of war rule if you like - there is however NOWHERE in the Quran that talks about slaughtering non-combatants indiscriminately or murder, something these young lads nowadays seem to have started doing as some kind of payback for their own causes