From Longman Dictionary of Contemporary Englishwhodunitwho‧dun‧it, whodunnit /ˌhuːˈdʌnɪt/ noun [countable] informal AMFALa book, film etc about a murder case, in which you do not find out who killed the person until the end
Examples from the Corpus
whodunit• It can be a considerable pleasure to the writer engaged in creating the now often somewhat despised simple whodunit.• He garbage-dispersed the whodunit concepts because it was always this monster woman behind the scheme to remainder the hero.• The whodunit tug is, of course, replaced by the where-did-he-go-wrong tug.• We all know the answer to this whodunit.• Unfortunately, it soon degenerates into an unconvincing whodunit.Origin whodunit (1900-2000) who done it? “who did it?” 