So, we should pre-emptively cancel Greta's passport/visa to the US....
Which would likely be met with general celebration....
We were talking about this at work.... mind control. Much like what very likely happened with Lee Harvey Oswald, and Jack Ruby. Someone talented in that field could play mind games, planting seeds of fear and distrust, and egg someone that is just a little off-kilter into taking action. I have heard that the CIA is very big into that... probably the FBI as well.
Find the "outsiders" and play on their phobias to set the bomb in motion....