UPDATE: Police have identified one of the two gunmen as Elton Simpson of Phoenix Arizona.

According to ABC News, 30-year-old Simpson was convicted as part of a terror investigation 5 years ago in which he was suspected of attempting to fly to Africa in order to train as a jihadi. A judge ruled that the government could not prove that Simpson was joining a terror group and placed him on probation.

FBI agents are now searching Simpson's Phoenix apartment and believe his roommate, Nadir Soofi, may be the second shooter. Simpson reportedly posted messages to Twitter prior to the shooting indicating that he wished to die as a martyr.

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Two gunmen were killed in Garland Sunday evening after they opened fire from a vehicle outside of an event featuring cartoons of the Prophet Muhammad.

The two gunmen began shooting shortly before 7 p.m. outside of the Curtis Culwell Center, which was hosting an event organized by a controversial group known as The American Freedom Defense Initiative. Garland ISD security officer Bruce Joiner was shot in the ankle before police opened fire on the gunmen and killed them. Joiner was treated at a local hospital and later released.

The City of Garland issued a statement describing the shooting on their Facebook page Sunday evening. (The embedded Facebook post may take several seconds to load.)

As today’s Muhammad Art Exhibit event at the Curtis Culwell Center was coming to an end, two males drove up to the front...

Posted by City of Garland, Texas Government on Sunday, May 3, 2015

Agents with the F.B.I. office in Dallas are assisting Garland police in an investigation of the shooting. As of Monday morning, authorities had not released the identities of the shooters or a definitive motive for the attack. Illustrations of Muhammad are considered sacrilegious and highly offense in most interpretations of Islam.

The Muhammad Art Exhibit offered a $10,000 top prize for the best caricature of the Prophet Muhammad and featured guests speakers including Geert Wilders, an outspoken critic of Islam and leader of the Netherlands Party for Freedom. The event's organizer, Pamela Geller, described the exhibit as a pro-free speech event in protest of the Charlie Hebdo attack and other violent events prompted by drawings of Muhammad.

In January of 2015, the Curtis Culwell Center hosted a pro-Islamic event, Stand With the Prophet in Honor and Respect, which drew several protesters. Organizers said the event was a fund-raiser to help combat negative depictions of Islam in the media.