Law enforcement and intelligence officials don’t owe a public explanation for everything they do. They probably had a good reason for letting him get as far as boarding the plane, and there may well have been a raft of LE and intel operatives on the plane to keep tabs on him. I’d be interested to know (but have no business knowing) whether his luggage, if any, actually made it onto the plane. My guess is that it didn’t.
Dumb ass.