ISIS has reportedly taken credit for a shooting in Garland, Texas Sunday that resulted in the death of the two gunmen at an anti-Islamic art exhibit.

SITE, an Islamic terror monitoring group, reported Tuesday that Twitter accounts linked to the Islamic State claimed responsibility for Sunday's attack and declared that Elton Simpson and Nadir Soofi of Phoenix, Arizona were acting as "soldiers of the Caliphate" when they opened fire from a vehicle outside of the Curtis Culwell Center shortly before 7 p.m. It is currently unclear whether the group is directly responsible or only making an opportunistic claim.

Authorities say Simpson was convicted a decade ago after lying to federal investigators when asked about a planned trip to Somalia. The FBI accused Simpson of attempting to make contact with a jihadi group in order to train as a militant, but a judge ruled that the government could not prove exactly what Simpson intended and placed him on probation. Investigators now say Simpson urged his Twitter followers to subscribe to an account known for issuing ISIS propaganda in the days leading up to Sunday's attack.

CNN reports that Simpson issued a tweet with the hashtag "#texasattack" reading "May Allah accept us as mujahideen" moments before he and Soofi began firing. He also indicated that he and Soofi had pledged allegiance to ISIS leader Abu Bakr al Baghdadi.

Simpson and Soofi were shot to death by a police officer after opening fire on the building where The American Freedom Defense Initiative's event was being held. There were no other fatalities, but a Garland ISD security guard was injured. He was treated at a nearby hospital and later released.