Why? The doors all had glass windows. She could see what was inside without entering the clearly secured space.
Secured space? Define that. The capitol has no spaces where deadly force is authorized merely for breaking in with zero evidence of being armed. Arrest, yes. Deadly force with no warning? Nope.
The black Brazilian dude simple acted the way he would have been allowed to...IN BRAZIL.
Nothing in US law or case law makes this legal.
The bigger “why” is why did the policeman fire a pistol at the neck of an unarmed woman, threatening nobody directly, when she was in a position of serious physical disadvantage?
He could and should have simply physically arrested her as she tried to climb down from being half in and half out.
Murder.