walk the beat(that's what the basic foot patrol police do: Before I became a Professor of Criminal Justice, I walked the beat in Chinatown for three years.Val_Ships)
internal affairs investigation(CNN, 2020: Philadelphia Police Commissioner said that while he was not privy to all of the information that led to the district attorney's decision to charge a police inspector, an internal affairs investigation on the matter had already been initiated and would continue regardless of the district attorney's prosecution.Alex_Odeychuk)