investigator vs police officer

investigator and police officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
investigator	Yes	No	No	No
police officer	Yes	No	No	No

As nouns, police officer is a hypernym of investigator; that is, police officer is a word with a broader meaning than investigator:

Other hypernyms of investigator include officer.

investigator (noun)	police officer (noun)
someone who investigates	a member of a police force
a scientist who devotes himself to doing research
a police officer who investigates crimes