If there was any possible chance he could escape and kill more people, then the police were justified in neutralizing the threat. That is not murder.
Now if the police incontrovertibly knew the perm was harmlessly contained except for rushing the cops in a suicidal move, then it MIGHT be murder.
This instance, since we don’t know any of the specific circumstances, we can’t say it was murder. If he was contained on the 1st story of the garage away from stairs and elevators, but they still worried he could jump to the ground and continue his killing spree, then the police are warranted to neutralize that threat.
Didn’t the Perp say he had planted bombs? How do you wait that out?