The heighten militarization of the police force in the US is a response to the heighten weaponry force used by unlawful criminals, such as what has been seen and used by terrorist's massacres.
A case of meeting fire power with fire power as it were.
One shouldn't make an excuse for illegally killing a person by brute force by an acting police officer doing their duty and the courts in this case I'm sure will reconfirm that.