Mohammed Contest Attack an ISIS First in the US
ISIS said it was behind the attack outside a contest in Texas featuring cartoons of Islam's prophet Mohammed. It is the first time the group claimed to have carried out an attack inside the United States.
Meanwhile, the FBI is under increased scrutiny for failing to prevent Sunday's attack after it had closely monitored one of the suspects in the shooting.
Federal agents had been monitoring 30-year-old Elton Simpson for possible terrorist ties for more than a decade.
Simpson and his roommate were shot dead after opening fire on a security guard outside the event.
In the past, FBI agents recorded Simpson talking about fighting "non-believers" for Allah and about plans to travel to Africa to link up with Islamist brothers in Somalia.
Five years ago, he was arrested for attempting to join an al Qaeda-affiliated group there. Years spent investigating Simpson for terrorism ties resulted in three years of probation, placement on the no-fly list, and $600 in fines and court fees.
His attorney says he became increasingly agitated.
"I mean, I know that some of the statements that he made were, 'If you die on the battlefield' than you get, you know, whatever, the wives and things like that. But I think you hear that out of a lot of people. I mean, that's a belief of the Muslim faith," Kristina Sitton, Simpson's attorney, said in 2011.
Simpson recently posted messages on Twitter about his dismay with his country. Just minutes before Sunday's shooting, he tweeted that he and a brother had pledged loyalty to ISIS.
"May Allah accept us as mujahideen [jihadists]," he wrote.
Though the FBI was aware of his social media rants, he was not under 24-hour surveillance.