I'm sure it varies wildly by place. You've got places where the rules are taken very seriously and places where the police chief is the mayor and has access to all the national law enforcement DBs with basically no oversight.
Given that policing is rife with various legal and ethical abuses in service of consolidating power and exerting control, it's hard for me to believe that there aren't places where police have deep access to government data on citizens.
Given that policing is rife with various legal and ethical abuses in service of consolidating power and exerting control, it's hard for me to believe that there aren't places where police have deep access to government data on citizens.