investigator vs expert

investigator and expert both are nouns.

Word	Noun	Adjective	Verb	Adverb
investigator	Yes	No	No	No
expert	Yes	Yes	No	No

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

investigator (noun)	expert (noun)
someone who investigates	a person with special knowledge or ability who performs skillfully
a scientist who devotes himself to doing research
a police officer who investigates crimes

investigator (adjective)	expert (adjective)
	having or showing knowledge and skill and aptitude
	of or relating to or requiring special knowledge to be understood