They were gonna do it, anyway. They were just waiting for an excuse. Any excuse. In a world as big and complex as ours, probability would have provided them with some pretext sooner or later. As we can see, they don’t know anything about the shooter, or his ideology. It’s just an excuse. If the world didn’t provide them one, they’d manufacture it. Walking around on eggshells and trying to avoid giving them one was never tenable.