By Ian Simpson and Mark Hosenball
WASHINGTON (Reuters) - U.S. investigators were looking into claims by the Islamic State militant group that it was behind a failed attack on a Texas exhibit of cartoons of the Prophet Mohammad in which two gunmen were killed, but officials said on Tuesday they doubted the group's direct involvement.
The Syria- and Iraq-based Islamic State (IS) said on its official online radio station that "two soldiers of the caliphate" carried out the attack on Sunday in Garland, a suburb of Dallas.
The White House said it was too early to tell if the two gunmen killed in Garland were tied to Islamic State. Spokesman Josh Earnest said many people try to capitalize on the influence of the group by claiming allegiance when they are not directly affiliated.
U.S. officials said while the claim of responsibility for the failed attack was being examined, investigators did not know whether the dead men launched the attack under instructions from IS or whether the group was opportunistically claiming credit when it had little or no direct or indirect involvement.
One U.S. official said investigators believed it was possible, if not likely, that Islamic State played an "inspirational" rather than "operational" role in the attack.
That would mean the shooters may have immersed themselves in items posted online by IS and other groups like al Qaeda in the Arabian Peninsula intended to incite violence, but that the group played no role in directing an attack on the Texas event.
U.S. investigators were going through the shooters' computers and communications devices, officials said.
"MIGHT HAVE SNAPPED"
Authorities said roommates Elton Simpson and Nadir Soofi of Phoenix were fatally shot by a police officer when they opened fire with assault rifles in a parking lot outside the cartoon exhibit and contest. An unarmed security guard suffered a minor wound.
The Simpson family said in a statement late Monday it was struggling to understand how it happened.
"We are heartbroken and in a state of deep shock as we grieve," it said. "We send our prayers to everyone affected by this act of senseless violence, especially the security guard who was injured in the line of duty."
Court documents showed Simpson had been under federal surveillance since 2006 and was convicted in 2011 of lying to FBI agents about his desire to join violent jihad in Somalia.
"I believe that perhaps he might have just snapped when he heard about the cartoon contest," Kristina Sitton, a Phoenix attorney who defended him in the case, told CNN.
Such portrayals are considered offensive by Muslims.
Soofi was a popular student at an elite school in Pakistan but struggled to adjust to life after moving to the United States as a teen, his friends said.
Soofi's story appeared to trace a familiar arc for some Western Islamists - disappointment, alienation, and a search for belonging that ended with the embrace of militancy.
The shooting in Garland, an ethnic melting pot in a city of about a quarter million people, was an echo of attacks or threats in other Western countries against images depicting the Prophet Mohammad.
In another Dallas suburb, Richardson, police were investigating an attack by two men on a worshipper leaving evening prayers at a mosque on Monday.
"It is too early to say whether this was a hate crime or an attempted robbery," said Richardson Police Sergeant Kevin Perlich, a spokesman.
The man was treated on the scene for minor injuries.
Police and federal agents had planned security for months ahead of the Garland event, organized by American Freedom Defense Initiative (AFDI), a free-speech organization that the Southern Poverty Law Center has described as a hate group.
(Additional reporting by Ahmed Tolba in Cairo, Katharine Houreld in Islamabad, David Schwartz in Phoenix, Arizona, and Julia Edwards in Washington; Writing by Jon Herskovitz; Editing by Jeffrey Benkoe)