A traditional forensic investigation begins with a classic question: whodunit?
Just what that is—and whodunit—remains the overarching plot that carries an electric current throughout the action.
"murder mystery," 1930, U.S. slang, originally a semi-facetious formation from who done it?
A mystery or detective story, play, movie, etc, esp a novel: a conventional whodunit
[1937+; fr who done it, ''who committed the crime?''; claimed as a coinage by and of various persons]