Their "religion" is simply a justification of their murderous lifestyle.
Let's call it what it is; Evil. Evil exists in this world. Some theologies assert that Satan cannot act in this world except through the actions of his willing accomplices. Unfortunately for good people of all faiths these accomplices can be found in all cultures, the Arab culture just makes it a little easier. Adolph Hitler was a baptized Roman Catholic, Joseph Stalin actually attended an Orthodox Seminary, Mao and Tojo were Buddhists. In each case their actions were both abominable and against the preachings of their faiths.
Yes religion is definitly used by the Jihadis to justify killing civilians. Islam is a vile religion. This is not to say all Muslims are evil, however my statement stands. Islam is a vile religion. One billion adherents and how many contribute to world peace?