They gave him plenty of opportunities to take another path...to not do what he was planning on doing.
His dad was so concerned that he contacted the FBI.
What part of crazy nutjob kid don’t you understand?
For goodness sakes...he thought the people who were throwing themselves off of the World Trade Center on 9/11 was “awesome”!
I'm sure he could have been busted for something (there's always 'conspiracy') early on. But then the FBI wouldn't have had a chance to cover itself with glory.