He was hired, performed the task he was hired for, and left, sounds like it to me.
Executives have used this for decades. Governments with armies hire mercenaries for the same reason, has gone on for centuries. Romans did it, it's so old. It's not a far off speculation here ... it's a well known, well practiced pattern of authoritarian behavior.
Why do you guys think bad cops who resign over and over keep getting hired the next city over?