Generally speaking, we will never know all the facts. If decisions must be made, we will make them with incomplete information.
And many of the "facts" in this case keep changing.
FWPD made the right decision to fire this officer immediately based on what they knew. That has not changed with any new "facts".
The DA made the right decision to prosecute this ex-officer for a crime based on what came out in a preliminary investigation. That has not changed with any new "facts".
The Courts have yet to convict or sentence the shooter. The outcome might very well be determined by new "facts" revealed during the pre-trial investigations. We are supposed to have a cautious judicial system that is restrained from casual judgments. That is a good thing.
Based on what has been revealed to date, I would vote for a 2nd degree murder conviction within two minutes of jury deliberation. But I have been on a jury before and been surprised by testimony that reversed my original opinions.
Your "facts" are not facts. You are wrong. The officer quit before he was fired.