Investigative work is built on selective mistrust. The difference between a state in which there are police and a police state is the scope of that mistrust. A state in which there are police will pursue criminals by using investigative techniques to profile suspects while a police state criminalizes everyone by treating the entire population of the country like suspects.
Some police states are smart, calculated power grabs. Others are dumb defaults. A smart police state suspects everyone because it's a tyranny. A dumb police state is run by people who can't or won't narrow down the suspect list so that they are forced to suspect everyone.
The United States has been on the road to becoming a dumb police state for a while now. It's not dumb because its law enforcement officers and military commanders are stupid. They are actually some of the best in the world. It's a dumb police state because fear of bigotry makes selective mistrust impossible.