The police are usually pretty good at their jobs, within reason. It's almost always going to take them several minutes at least to respond to your call, but when they do manage to arrive on the scene they are usually pretty good about eliminating the threat and rendering first aid/etc. There are some infamous cases where this severely broke down, instances of cops not entering an active crime scene and instead seeing fit to stop the public from taking matters into their own hands, but these instances are so notorious because of how unusual and counter to American values they were.

It's usually prosecutors and judges who drop the ball.