PHOENIX (AP) — The Islamic State group claimed responsibility Tuesday for the assault on a Texas cartoon contest that featured images of the Prophet Muhammad, marking the first time the terror group has taken credit for an attack in the United States. But it was unclear whether the group actually directed Sunday's shooting in the Dallas suburb of Garland or if the two gunmen were inspired by the group to act on their own before they were shot and killed. Such lone wolf attacks pose a daunting challenge to law enforcement, and IS has a history of claiming responsibility for attacks in which it played no operational role, counterterrorism experts said. Federal officials identified the gunmen as Elton Simpson and Nadir Soofi, both Americans who lived in Phoenix.Read more on NewsOK.com