There were pictures. There was a picture of the cop with the gun raised and his finger on the trigger with her NOT or not yet in the window. With his finger on the trigger he had already determined or been told to shoot someone.
And the man casually walking across the hallway in the background... prolly the action signal.
It was staged.
Entering through the window was justification enough. Honest people use doors. She was perceived to be a threat to the safety of the representatives who sought refuge in that room. She was the vanguard of a larger incursion.