Horseshit! I firmly believe they were monitoring every minute and had no intention of stopping him doing what they desired.*
*Yes I know you were being sarcastic.
They may well have been looking for a mass casualty event in a Conservative State, albeit Fargo is probably the most Liberal town in the state not on an Indian Reservation. Remember, the current administration in DC wants to take our guns and can always use a distraction timed to blow the next revelation off the front page and airwaves.
How many of his internet contacts were Feds?