Once again, please post a link to a federal, state or local law that prohibited the use of lethal force when the perp was armed and had used lethal force already against the officers on the scene.
No one has yet.
EXCESSIVE FORCE
A law enforcement officer has the right to use such force as is reasonably necessary under the circumstances to make a lawful arrest. An unreasonable seizure occurs when a law enforcement officer uses excessive force in making a lawful arrest.
Now someone did.