After recently reading a couple of reviews of The Death of Laurence Vining (here and here) I was reminded of this short story (originally printed in the April 1965 edition of Ellery Queen's Mystery Magazine) with a similar premise--an impossible murder in a hotel elevator. Charles Kimball (an illusionist who goes under the stage name of Dr. Satanus) is found dead from a stab wound in the Hotel Bowman elevator. Two witnesses (including Kimball's wife) testify that he entered the elevator alone and that the car made no stops as it descended to the lobby where his body was discovered. Furthermore, the emergency exit in the roof of the car is locked from the inside. Who killed Kimball and how was his death carried out?
When it comes to my preference in impossible crimes, the more simple the explanation of the mystery the better and so I found "The Impossible Murder of Dr. Satanus" with its straightforward solution to be a satisfying impossible crime story.
According to the bio in EQMM, Krohn was a university freshman when this story was published and the first detective story he read was (surprise!) John Dickson Carr's The Three Coffins. Although he started his writing career young, it doesn't appear that he published much (if anything else) in the genre. Too bad because this was a promising debut.
I thought this might be an obscure short story to get a hold of, but it was deservingly reprinted in 2007 in The Mammoth Book of Perfect Crimes and Impossible Mysteries.