ISIS claim responsibility for Texas attack

Chilling private Twitter messages sent by one of the gunmen who attacked an anti-Islam event on Sunday show how he had turned against the U.S. - and intended to join ISIS.

Elton Simpson, 30, and his roommate, Nadir Soofi, 34, were shot dead outside a contest featuring cartoons of the Prophet Muhammad in Garland after one of them fired at an unarmed security guard.

Now it has emerged that Simpson had spoken about the controversial event in private Twitter messages ahead of the attack, according to ABC News.

Any physical depiction of Muhammad - even a respectful one - is considered blasphemous in Islam, and drawings similar to those featured at the Texas event have sparked violence around the world.

'When will they ever learn?' Simpson wrote in a message in March, according to ABC.

Messages sent earlier that month also show how he was turning against the U.S.

'Soon you won't be able to live in America as a Muslim. The noose is tightening,' he wrote.