Easy. Since the kids are the priority, that is the very first matter the cops should have gotten out of the way, find out where they were (in the car), then go to the car first make sure they are away safe. If the intent was to arrest the guy, the kids planning for where the kids are, or where they should be placed has to be the first priority.
Second, make sure the people milling around the car are safe, back in their houses or cars, and talk to them. That wasn't done. What was the third officer doing that wasn't in the video?
Third, if the guy wants to run, let him. The cops already have his kids. Dad will come back. There will be plenty of opportunities to snag him. If he is running, he is not posing a danger to the public or the police.
If, like you say, the police went in knowing he was dangerous, they would have called for more backup. Apparently 3 police were not enough. He was clearly free at that point to drive and shuttle his kids around.
Since there was no visible weapon there was zero reason to draw their weapons until AFTER he retrieved whatever weapon the police figured he was going for it his car. The officers should have backed off, got people to safety, and called for backup, and kept their distance and tried to deescalate the situation. If they did not posess those skills, then call for a negotiator.
The mistakes the cops made that are evident in that few seconds of video make it clear that:
- The cops were not in fear for their lives and they were not wearing bullet proof vests
- They lost control of the situation, and clearly never were able to get control if their tasers did not work
- If the guy was getting his weapon in the car, the 3 cops "knowing" he was dangerous in advance, they should have first secured the car
- The guy was not running, he was walking to his car
- The close proximity of the public with drawn weapons indicates officers demonstrated no concern for public safety
- The second cop should have ran around to the passenger-side door to see if it was open and would have had visibility on what the guy was reaching for or doing after he opened the door
- Tugging on a shirt, wtf is that all about? Tackle him and engage him physically, since the previous tasering didn't work
- The shooter cop fired 7 bullets at point blank range and the guy is still alive? How?
I've not seen any videos of tactical experts explaining the situation, so that, as a layman, are my first impressions of the situation.
Anyone that is defending an individual officer's "right" to repeat such an atrocity and has zero input to prevent it from happening again is part of the problem.