Note that he doesn’t just say, “May Allah accept us as mujahedeen,” but adds the hashtag, #texasattack, strongly suggesting that he expected to become a mujahid at our AFDI/Jihad Watch Muhammad Art Exhibition and Cartoon Contest.
“Bay’ah” is allegiance, and “Amirul Mu’mineen” is the Leader of the Believers, i.e., the caliph. The possible shooter is saying he had pledged allegiance to the Islamic State.
One of those attending the event wrote to me: “On the way home, the officer driving said that the gunmen were trying to enter the building to shoot the place up when they were stopped. It seems obvious in retrospect, but that detail eluded us as we were waiting in the various secure locations.”