"A woman who was seated near the gunman said something seemed off from the moment the gunman entered the church. Besides never seeing the man in church before, he also appeared to have a beard and a wig that looked fake. “I should have listened to my gut,” Isabel Arreola, 38, told the Fort Worth Star-Telegram. “While he was there, I couldn’t sing. I couldn’t pray. There was just something not right about him."
I highly recommend the book
"The Gift of Fear", by Gavin de Becker. This woman's statement perfectly illustrates what the book so well articulates.....
When you know, you know....
Fake beard & wig (see it fly off his head when he get's popped), wearing a large bulky jacket when no body else is.
I think the security team read the tea leaves correctly and were keeping their eyes on this turd, but were apparently way too charitable in giving him the benefit of the doubt (perhaps out of a motive to be kind to the poor lost soul seeking redemption).
Better to initiate the contact yourself and in doing so seize the initiative. Closing the distance while the suspected BG is still concealing his intent and saying "Hi there, is there anything I can do to help you" said with an extended hand will very quickly give you a lot of information about them.... Sitting down next to him and asking "Why are you wearing that silly get up?, are you hiding something?"
Notice he doesn't draw the shot gun and fire rapidly... it actually takes him time to stand up and pull it out. If someone was right on top of him, it would have turned into a tussle and could have perhaps achieved a different outcome.
Again, when you know, you know.... ACT ON THAT KNOWLEDGE!
There are several constructive things that could have been done to disrupt this premeditated attack short of drawing on the guy.