Blind Justice (1934)
Blind Justice is a 1934 British thriller film directed by Bernard Vorhaus and starring Eva Moore, Frank Vosper, Geraldine Fitzgerald, Roger Livesey and John Mills. A woman is blackmailed by a criminal, who has discovered that her brother was shot as a coward during the First World War. It was based on Recipe for Murder, a 1932 play by Arnold Ridley. A review of the play, mentioning the forthcoming film, was the first use of the word whodunit it print.
More at Wikipedia.