Simpson takes responsibility for the shooting on Twitter, around 20 minutes before the shooting starts.
The bro with me and myself have given bay’ah to Amirul Mu’mineen. May Allah accept us as mujahideen. Make dua #texasattacks
Bay’ah means to give an oath of allegiance, to Amir al-Mu’minin or Abu Bakr al-Baghdadi, the leader of ISIS. “Make dua” means to call out in prayer. He also tells his users to follow @_AbuHu55ain, who posts about the shooting before the account was suspended.