ISIS is claiming responsibility for an attack at a center near Dallas that was exhibiting cartoon depictions of the Prophet Muhammad. An audio statement on the extremist group's al-Bayan radio station says that "two soldiers of the caliphate" carried out the Sunday night attack; both men, identified yesterday as Elton Simpson and Nadir Soofi, were shot dead. The ISIS statement says: "We tell America that what is coming is more bitter and harder and you will see from the soldiers of the Caliphate what harms you." It did not provide details and it's unclear whether the group is opportunistically claiming the attack as its own. USA Today points out ISIS has never before claimed responsibility for an attack that occurred within the US.