By David Schwartz
PHOENIX (Reuters) - The Islamic State militant group claimed responsibility on Tuesday for an attack on a Texas exhibit of caricatures of the Prophet Mohammad in which the two gunmen were killed.
The Syria- and Iraq-based Islamic State claimed responsibility on its official online radio station, saying "two soldiers of the caliphate" carried out the attack on Sunday in Garland, Texas. Experts warn that militant groups have been known to claim credit for attacks in which they were not involved.
U.S. government sources close to the case have said investigators were scouring electronic communications sent and received by the dead gunmen, roommates Elton Simpson and Nadir Soofi, of Phoenix, for evidence of contacts between them and militant groups overseas, most notably Islamic State.
Simpson and Soofi were killed by police when they opened fire with assault rifles at the cartoon exhibit and contest. An unarmed security guard was wounded.
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.
"It certainly was a ... completely provocative event and I would see many people who were devout about their religion being upset."
Garland Mayor Douglas Athas said he did not make the decision to hold the exhibit in town, since the local school district owned the building where it was held.
The shooting in Garland, a Dallas suburb, was an echo of attacks or threats in other Western countries against images depicting the Prophet Mohammad.
In January, gunmen killed 12 people in the Paris office of French satirical magazine Charlie Hebdo in what was said to be revenge for its cartoons. Such portrayals are considered offensive by Muslims.
Police and federal agents had planned security for months ahead of the event, organized by American Freedom Defense Initiative (AFDI), a free-speech organization that the Southern Poverty Law Center has described as a hate group.
Sitton said Simpson had never shown any desire to join violent jihad.
"It just sounded like a lot of talk especially compared with his demeanor when I was speaking with him and when I met with him," she said.
(Additional reporting by Jon Herskovitz in Austin, Texas; Ahmed Tolba in Cairo, Egypt; Writing by Ian Simpson; Editing by Jeffrey Benkoe)