Iran purposely shot down the airplane, PERIOD! They, at the time, wanted to destroy the aircraft and thinking it was a hostel plane does not cut it. Now it was a mistake, sure it was, but hindsight is no excuse. They purposely killed .
I don’t have a theory, but rather a question.
Just suppose that the guy who fired the missile is/was a rebel against the regime?
Firing the missile and claiming it was a mistake in order to bring international anger against the regime.
Whether he is still alive would give us a clue.