At least some number of people will have the crucial parts of the plan in their minds, though. The parts that could thwart the whole plot if those parts were to

At least some number of people will have the crucial parts of the plan in their minds, though. The parts that could thwart the whole plot if those parts were to be discovered by law enforcement. Of course, law enforcement may not know who those people are or even that an attack is imminent without pre-emptively monitoring every single person's thoughts so it can be detected with sufficient time to stop it, like how cop cars and (I think) speed cameras pre-emptively and automatically scan every license plate they can detect.