When Kathleen is unsuccessful at following a suspicious character for her boss, she tells him he should have hired William Powell as a secretary instead. Powell played the detective in the Thin Man and Philo Vance movie series.
In later years, Lucille Ball was vocal about hating the experience of shooting "The Dark Corner". The lion's share of her resentment was pointed at director Henry Hathaway, whose bullying reduced Ball to stuttering on set, at which point Hathaway accused her of being inebriated.
The trivia item below may give away important plot points.
After Stauffer falls from the window, his cab driver says "How'd I know he was going to take a Brodie?". This is a reference to Steve Brodie, the first man to survive the 135 foot jump from the Brooklyn Bridge (1885). His survival was a media sensation at the time, and the phrase "pull a Brodie" and variants has been used by New Yorkers since.