The Stooges are private eyes at the Alert Detective Agency who are called upon by the wealthy Mr. Goodrich (Emil Sitka). Goodrich reports that the Phantom Gang, of which his own niece (Christine McIntyre) is a member, have been murdering socialites, with Goodrich as their next target. By the time the Stooges arrive, Goodrich is out cold and locked away, with the butler (Charles Knight) (also a member of the Phantom Gang) greeting the trio. Goodrich's niece flirts with Shemp, ultimately trying to poison him. Finally, a towering monster goon named Nikko (Duke York) chases the Stooges from room to room. After Shemp knocks Nikko cold, he literally bumps into an unconscious Goodrich, who spills the Phantom Gang's plot. A fight then ensues with the lights out, and the Stooges ultimately get the baddies.
- Moe Howard as Moe
- Shemp Howard as Shemp
- Larry Fine as Larry
- Emil Sitka as Mr.Goodrich
- Dudley Dickerson as Henry The Janitor
- Christine McIntyre as Delores
- Ralph Dunn as Gang leader
- Duke York as Nikko
- Charles Knight as Crandall
- Who Done It? is a remake of Pardon My Terror starring Richard Lane and Gus Schilling. Pardon My Terror was actually written for the Stooges, but jettisoned by Director Edward Bernds when Curly suffered his debilitating stroke in May 1946.
- This short was reworked again in 1956 as For Crimin' Out Loud, using ample stock footage.
- Who Done It? was filmed on December 9–12, 1947. But it wasn't released until 15 months later on March 3, 1949. As the short was edited in early 1949.
- Who Done It? was the last the original Stooge short to be filming in 1947.
- In ending scene Shemp was confused about people in living room, he look down to Moe and Larry. Then unknown reason that Shemp look to Emil Sitka's on right as Larry, but Larry was left nearly from Moe's where he get knocked out by Shemp with fireplace shovel.