Every situation is different. If shot at, return fire and eliminate the threat. It is kill or be killed.
You find out what happened, train others so it wont happen again, and support the agents if they did as one would expect them.
It is better if the shooters dont know who they shot, as in were buddys prior, or for the shooters to see photos, go to the funeral, or talk to family.
One thing you dont want is a cover up like the Rangers, where Pat Tillman was killed. Its more acceptable in the Military, but still a sad situation.
If you shoot first you should have PID, Positive IDentification of a threat target. If shot at, you should return fire .
Anytime you have people in high stress situations that are armed, you have a chance of blue on blue. Even with training you can only do so much.
Counseling can only do so much, but if the shooters did what would be expected it can help.
We need more restrictions on the 1st Amendment and less on the 2nd Amendment.