We've remarked on the killer's unprofessional conduct. A real police officer would never have let that situation develop the way it did.
I believe that the events of the previous year have implanted in the minds of ICE agents that because the people they are persecuting are subhuman, they don't need to have any regard for their civil rights. Therefore, they can mete out violence with ample "justification."
A truly shocking number of MAGAs think, based on what they've repeatedly said, that civil and human rights apply only to Americans. That's why ICE utterly disregards due process, protections against search and seizure, procedures to identify suspects, and of course, whatever silly little rules say you shouldn't kill suspects on the spot even if you ARE mad at them.
So with that mindset firmly in place, they can extrapolate it to apply to anyone who gets in their way, brown person or not.
You're correct that when someone draws a gun, points it at you, and screams at you to get out of your car, you should do exactly that... immediately. It would help in these situations to yell "I love Dear Leader Trump!!" over and over, as that may add a couple of seconds to your life before they kill you anyway.
Most law enforcement personnel are highly professional. It used to be that police candidates were selected based on their ability to fight; to be violent when the situation called for it. Nowadays, they're selected for their ability to remain calm and de-escalate situations.
If that ICE thug had been trained that way, and not selected for his willingness to mete out violence, that poor woman would still be alive.