Wikipedia: Murder, Inc.
Murder, Inc. (or Murder Incorporated) was the name the press gave to organized crime groups in the 1930s through the 1940s that acted as the "enforcement arm" of the American Mafia, the early organized crime groups in New York and elsewhere. Originally headed by Louis "Lepke" Buchalter, and later by Albert "The Mad Hatter" Anastasia, Murder, Inc. was believed to be responsible for between 400 and 1,000 contract killings, until the group was exposed in the early 1940s by informer and group member Abe "Kid Twist" Reles. In the trials that followed, many members were convicted and executed, and Abe Reles himself died after mysteriously falling out of a window. Thomas E. Dewey first came to prominence as a prosecutor of Murder, Inc. and other organized crime cases.
(Oxford English Dictionary)
Murder, Inc., an organized network of gangsters in the United States founded in the 1930s by Louis 'Lepke' Buchalter to carry out assassinations and assaults for money; (more generally) any group of organized and violent criminals. Murder, Incorporated = Murder, Inc.
18 March 1940, New York (NY) World-Telegram pg. 4, col. 3:
As prominent as Reles and Goldstein were in gang circles, neither of them was the president of Murder, Inc.
22 April 1940, New York (NY) Times, pg. 14, col. 5:
The principal speaker..drew a parallel between 'Murder Incorporated', recently uncovered by Brooklyn District Attorney William O'Dwyer's investigations, and 'Moral Murder Incorporated' as represented by the cloak of academic freedom thrown around a man and his pagan theories of sex morality'.