The series ground to a halt when Edna May Oliver left her RKO contract in 1935. The studio tried to continue the series with different actresses but audience interest was negligible and original novelist Stuart Palmer was not happy about this attempt at all.
The New York Aquarium, where the Penguin Pool Murder is set, was located on the southern tip of Manhattan in Battery Park from 1896 until it was closed in 1941. It has been located in Coney Island since 1957.
The telephone operator (Rochelle Hudson) calls Hildegarde Withers (Edna May Oliver) "Lydia Pinkham." The reference is to the woman who brewed alcohol-based elixirs touted as a "women's tonic" said to relieve menstrual and menopausal pains.
The Ruth Snyder - Judd Gray murder case alluded to by Inspector Piper was a notoriously inept crime of passion committed in 1927. Both Double Indemnity (1944) and The Postman Always Rings Twice (1946) were inspired by the case, according to their author James M. Cain.
The first of three appearances by Edna May Oliver as Hildegarde Withers, the others being Murder on the Blackboard (1934) and Murder on a Honeymoon (1935).