ISIS is claiming responsibility for the attack on a Muhammad cartoon event in Garland, Texas.

This is the first time that the terror group has taken credit for an attack in the United States. Still, there’s no proof that ISIS had contact with the two roommates who died in a shootout with police.

The terror group made the claim on its Al Bayan radio station, where it called suspects Elton Simpson and Nadir Soofi “two soldiers of the caliphate.”

Investigators are now poring over the social media profiles of the two suspects.

Meanwhile, Simpson’s family said in a statement, “We are sure many people in this country are curious to know if we had any idea of Elton’s plans. To that we say, without question, we did not.” reported:

An investigation following the attack revealed a striking connection between at least one of the gunmen and a Twitter account based overseas, suggesting that ISIS operatives had knowledge of the attack beforehand and that the same fighters encouraged the shooters, a counterterrorism source told Fox News.

One British-based jihadi in Syria who does not tweet on a regular basis sent out a message within an hour of the attack, praising both men.

Another established ISIS Twitter account suggested he had been in contact with one of the gunmen just prior to the attack, using messages such as he tried to reach him but just missed him. The source said the social media appeared to show encouragement and mentoring.

Muhammad Cartoon Event Organizer: 'There's a Violent Assault on Free Speech'

'Once Free Speech Goes, It's Over': 'Draw Muhammad' Contest Winner Sounds Off