They kill people because of who they are and they kill people because of what they believe. And it's indiscriminate. They kill Shia. They kill Yezidis. They kill Christians. They kill Druze. They kill Ismaili. They kill anybody who isn't them and doesn't pledge to be that.
Source, in full
"Remarks to the Staff and Families of U.S. Embassy, Paris" (17 November 2015) on the November 2015 Paris attacks; also quoted in "John Kerry: Charlie Hebdo Attack Had ‘Legitimacy,’ ‘Rationale’ Behind It" by Alex Griswold, mediaite.com (17 November 2015)