war criminal vs offender

war criminal and offender both are nouns.

Word	Noun	Adjective	Verb	Adverb
war criminal	Yes	No	No	No
offender	Yes	No	No	No

As nouns, offender is a hypernym of war criminal; that is, offender is a word with a broader meaning than war criminal:

war criminal: an offender who violates international law during times of war
offender: a person who transgresses moral or civil law

Other hypernyms of war criminal include wrongdoer.

war criminal (noun)	offender (noun)
an offender who violates international law during times of war	a person who transgresses moral or civil law