murder mystery vs mystery

murder mystery and mystery both are nouns.

Word	Noun	Adjective	Verb	Adverb
murder mystery	Yes	No	No	No
mystery	Yes	No	No	No

As nouns, mystery is a hypernym of murder mystery; that is, mystery is a word with a broader meaning than murder mystery:

murder mystery: a narrative about a murder and how the murderer is discovered
mystery: a story about a crime (usually murder) presented as a novel or play or movie

Other hypernyms of murder mystery include mystery story, whodunit.

murder mystery (noun)	mystery (noun)
a narrative about a murder and how the murderer is discovered	something that baffles understanding and cannot be explained
	a story about a crime (usually murder) presented as a novel or play or movie