Idiom of the day :- Whodunnit

Usage, examples and definition of the Idiom :-

A detective novel or play A : My Aunt Nellie loves to read whodunnits so I send her an Agatha Christle each birthday. She’s read about so many murders over the years she must be an expert by now. B : Yes I’m sure. How is her husband, Uncle George ? Do you send him presents as well ? A : Now that’s strange. You know I haven’t heard from him for ages. This expression is an abbreviation of the question ‘Who has done it ?’ This of course means’ Who did the murder ?’ All crime novels and plays contain this puzzle which the reader attempts to solve.