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GARLAND (CBSDFW.COM/AP) – The terrorist group ISIS has claimed responsibility Tuesday for the attack at the Curtis Culwell Center in Garland, saying that the two men who died were on a mission, according to a statement which was released on a jihadist-affiliated radio station.

The audio statement Tuesday on the group’s Al Bayan radio station said that “two soldiers of the Caliphate executed an attack on an art exhibit in Garland, Texas.”

The French news agency AFP quoted the group as saying, “This exhibit was portraying negative pictures of the Prophet Mohammed.”

According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad — even a respectful one — is considered blasphemous, and drawings similar to those featured at the Texas event have sparked violence around the world.

The statement goes on to say, “We tell America that what is coming is more bitter and harder and you will see from the soldiers of the Caliphate what harms you.” It was the first time that ISIS, which frequently calls for attacks against the West, had claimed responsibility for one in the United States.

It was unclear whether the group, which has captured large swaths of territory in Syria and Iraq, had an actual hand in the operation, or whether the two suspects had pledged allegiance to the group and then carried out the attack on their own.

There was no immediate independent confirmation of the claim, however, the Garland Police Department and the FBI have been investigating the background of the suspects since they were shot and killed by an officer on Sunday evening.

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The attorney who previously represented suspect Elton Simpson in a 2010 terrorism-related case stated that he seemed harmless. Simpson was charged with make false statements concerning terrorism, but he was never convicted of having terror ties. “He was very devout. He was very vocal about being devout,” said lawyer Kristina Sitton. “He was very vocal about attempting to convert other people and asking other people what their religion was and why they believed in that religion versus his religion.”

“I never saw any indications that he was violent,” Sitton continued. “He was always peaceful with me, even to the point where I think I got more riled up about the charges than he did, because I thought they were absolutely outrageous.”

Simpson’s family said that they are heartbroken about the attack, and had no idea about his plans. The family released a statement saying that they do not condone violence and support the men and women in law enforcement.

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Meanwhile, the mother of suspect Nadir Soofi said that her son was brainwashed, and she does not blame the police for killing him. Soofi grew up in Garland, and his mother now lives in Houston. She is still trying to understand what really happened to her 34-year-old son. His father, from Pakistan, raised him around the Islamic faith.

Sharon Soofi believes that her son’s roommate, Simpson, was the person behind the attack. “I’m thankful he did not kill anybody,” she said. “When your child dies under these kinds of circumstances, it just leaves you numb and empty.”

Soofi had an 8-year-old son whom, his mother said, he adored. “He wasn’t a violent person,” the mother added. “I can’t imagine what went through his mind.”

Garland Police Department spokesman Joe Harn did not immediately respond to an email Tuesday morning asking for reaction to the new developments.

The Curtis Culwell Center opened in 2005 and brings together almost a million people each year for community events including concerts and weddings. In fact, schools from all over North Texas are set to hold graduation ceremonies there throughout the month of May. The Garland Independent School District is contacting those schools — about 30 total — to calm any fears.

The school district is also reviewing security plans to make sure that anyone attending an event at the center is safe.

Students arrived at the Curtis Culwell Center on Tuesday morning for AP testing with the Sunday shooting still fresh on their minds. About 350 kids from high schools around the district are expected there on Tuesday. “I’m a little sketched out,” said Rowlett High School student Conner Hedrick. “I must say, all the security around and stuff, it’s kind of a bad testing environment, but it is what it is.”

“Didn’t think something like this would happen so close to my school,” said Naaman Forest High School student Carlos Mendoza. “It kind of just shocked me.”

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