Everyone knows me here and knows that no one is more empathetic for LEO concerns than I am. That being said, I disagree with your first statement.
A police officer may use force, however, regardless of his "perception" he does not get, "a pass" as fileboy put it.
If an officer's perception is wrong or he used force that is unwarranted, then no matter what the officer's "perception" was, he can face very serious consequences.
Possibly I am disagreeing with the way you worded your statement and there really is no disagreement. I'm not completely sure.
On the other hand, I disagree with fileboy that this can be categorized as, "abuse" on the police officer's part. An accidental shooting is an accidental shooting, however, that does not justify or excuse the officer in question from facing serious repercussions....
I do agree that right now not all the facts are out.
Nothing is impossible for the person that doesn't have to do it.