Police detective and Private investigator

Police detective noun - A police officer who investigates crimes.

Private investigator and police detective are semantically related in detective topic. In some cases you can use "Private investigator" instead a noun phrase "Police detective", when it comes to topics like private detective.

Private investigator noun - A person not on the police force who investigates criminal or illicit activity or searches for missing persons.

Police detective and private investigator are semantically related in detective topic. You can use "Police detective" instead a noun phrase "Private investigator", if it concerns topics such as private detective.