"A Shriek Of Death - As The Sleek Nocturnal Prowler STRIKES Again!"
The police arrest a man climbing over the wall of a cemetery after midnight. He claims that he is being blackmailed and is following instructions he received by mail to leave $1000 on a certain grave. It turns out that he's not the only one who got a blackmail letter from the same person--calling himself "The Black Panther"--and it also turns out that all the recipients are connected to an opera company.
Police Commissioner Thatcher Colt

Anthony 'Tony' Abbot (as Ricki Vallin)

Everett P. Digberry

District Attorney Bill Dougherty

Miss Spencer
Capt. Edgar Walters / Frank Galloway

Nina Politza
Enrico Lombardi
Police Captain Mike Flynn

Officer Murphy

Police Captain Tom Henry
Samuel Wilkins

Antonio Spogucci (as Joseph M. De Villard)
Guiseppe Bartarelli (as Jack Vanaire)
John Martin George (as William Castello)

Officer Lou Levinsky (as Harry Clarke)
Apartment Manager (as Lou LeRoy)
Nicodemus J. Brown

Petunia

Coroner
Joe Morgan
Police Sergeant Flanagan (as Casey McGregor)
Hotel Manager Stevens
Lombardi's Police Escort (uncredited)