Should be the same exact justification afforded to citizens.
Right now, the rules governing use of deadly force for a citizen are extremely limited.
Emptying an entire magazine from two weapons into a someone we felt 'threatend by' would be an anal examination by the same agency that absolves what their agents are permitted to do to citizens.
Um...that video shows a textbook-perfect case of shooting in self defense, civilian or cop. Including the number of rounds. (Yes, I’ve had hundreds of hours of training on the subject.)