Interesting account of what happened from a Pentagon spokesman.
Now the Pentagon has previously claimed the engagement was in self-defence of the forces they were protecting. Which would be a valid defence if the SU-22 was clearly manoeuvring to drop bombs of strafe them and the actions were taken to prevent the attack.
However this account makes it clear that the engagement took place
after the SU-22 had attacked and was now clean winged and egressing the area - the justification of self-defence no longer applies. It doesn't mean it was wrong - if the SU-22 was now considered a Hostile having committed a hostile act and if the current ROE authorised engagement - but the rationale of self-defence cannot hold.
New details on US shoot down of Syrian jet - CNNPolitics.com