American police have an institutional problem with violence.
It flows out of the war on drugs which has led to the increasing militarization of police officers. If you keep telling cops they’re in a war, it comes as no surprise when they start to act like it.
For Further Reading
Weapons of War on our Streets: A Guide to the Militarization of Police
Executive Order Takes Window Dressing off Police Militarization Program
Department of Defense Writes to the Tenth Amendment Center on Police Militarization