1927 in organized crime
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- Al Capone's Chicago Outfit earns a yearly income of $108 million.
- Salvatore Maranzano is sent to New York by Sicilian Mafia Don Vito Cascio Ferro in an attempt to unify the New York Italian-American gangs into a single organization.
- Chicago bootlegger Manley Sullivan becomes the first gangster to be convicted for federal tax evasion. The case would establish the precedent of illegal income being taxable, an effective weapon against organized crime figures throughout the decade.
- Chicago gambler Jacob "Monte" Tennes agrees to sell his remaining shares of the Chicago Racing Wire service to newspaper publisher Moses Annenberg.
- The Southside O'Donnell's gang kidnaps John "Jackie" Adler, a Capone liaison to the Chicago police. Adler is held for,[clarification needed] but is later released unharmed.
- Angelo Lo Mantio, a Milwaukee, Wisconsin gunman, is hired by the Aiello Brothers to murder Al Capone.
- Capone gunman Louis LaCava is forced to leave Chicago after failing to take over the Cicero, Illinois area.
- Sam Valante, recently hired by Chicago gangster Joe Aiello to kill Al Capone, is himself killed while arriving in Chicago. New York gangster Antonio Torchio, also hired by the Aiellos to kill Al Capone, is killed by Capone gunmen as he steps off a train arriving in Chicago.
- Sydney, Australia, gangster Norman Leslie Bruhn is killed on the orders of John 'Snowy' Cutmore.
- January - Chicago saloon owner John Costanaro, a distributor for the Ralph Sheldon Gang, is killed by a rival bootlegging gang.
- January 6 - Theodore Anton, a restaurant manager above Al Capone's Hawthorne Inn, is kidnapped and later killed by the rival North Side Gang.
- March 11 - Saltis-McErlane gunmen Charles "Big Hayes" Hubacek and Frank "Lefty" Koncil are killed, possibly by Capone gunman in retaliation for Koncil's recent acquittal for the 1926 murder of Sheldon member John "Mitters" Foley, while driving through Southside O'Donnell's territory.
- March 28 - Milwaukee, Wisconsin crime family leader Joseph Amato dies of natural causes and is succeeded by Joseph Vallone.
- April 4 - North Side Gang leader Vincent Drucci is killed by Chicago Police detective Dan Healy while in police custody.
- June 10 - While checking up on Frankie Yale's bootlegging operations in New York, Capone gunman James DeAmato is killed in Manhattan.
- July - Ray Hyland, a gunman for Charles Birger, and Birger associate Arthur Newman are convicted of murder and sentenced to life imprisonment.
- August 7 - After being stopped by a US Coast Guard cutter off the eastern coast of Florida, "King of the Rum Runners" James Alderman kills a US Secret Service agent and two members of the Coast Guard while being arrested. Alderman is later convicted of murder and hanged in 1929.
- September 9 - Alphonse Palizzola "Green Ones Gang" member killed (also 10-year-old boy)
- October 13 - Cleveland, Ohio gangster Joseph Lonardo is killed in a local barber shop, along with his brother John, by members of the Porrello gang. Salvatore Todaro subsequently assumes leadership over the Porrellos.
- October 16 - New York labor union racketeer Jacob Orgen is killed by Louis Buchalter and Jacob Shapiro. Orgen's bodyguard Jack Diamond is severely wounded in the attack but would survive.
- October 26 - A shootout between Melbourne and Sydney, Australia, gangsters Joseph 'Squizzy' Taylor and John 'Snowy' Cutmore results in both men being fatally wounded.
- December 28 - Vito Gannola "Green Ones Gang" member shot 37 times and killed by two men claiming to police officers while hiding in his mistress house
Arts and literature
- Josef von Sternberg's Underworld is released starring George Bancroft, Evelyn Brent, Clive Brook, Fred Kohler and Helen Lynch. 
- Joseph Ferriola (Joe Nagall), Chicago Outfit syndicate leader
- Christopher Furnari, "Christie Tick", Lucchese crime family member
- James LaPietra, Chicago Outfit syndicate leader (Southside) and brother of Angelo LaPietra.
- Ono Toshifumi, Ichiwa-kai Yakuza leader
- January 2 - Vincent Meli, Detroit crime syndicate leader
- March 29 - Michael Rizzitello, Los Angeles crime family Capo
- December 26 - Louis R. Failla, Patriarca crime family soldier
- Norman Leslie Bruhn, Sydney gangster
- Sam Valante, Aiello Gang member
- January - John Costanaro, Chicago saloon owner and associate of the Ralph Sheldon Gang
- January 6 - Theodore Anton, Chicago Outfit associate
- April 4 - Vincent Drucci, North Side Gang member
- March 11 - Charles "Big Hayes" Hubacek, Saltis-McErlane gunman
- March 11 - Frank "Lefty" Koncil, Saltis-McErlane gunman
- March 28 - Joseph Amato, Milwaukee crime family leader
- June 10 - James DeAmato, Chicago Outfit gunman
- September 9 - Alphonse Palizzola "Green Ones gang" killed
- October 13 - Joseph Lonardo, Cleveland gangster
- October 13 - John Lonardo, brother of Joseph Lonardo
- October 16 - Jacob Orgen, New York labor union racketeer
- October 26 - John "Snowy" Cutmore, Sydney gangster
- October 27 - Joseph "Squizzy" Taylor, Melbourne gangster
- December 28 - Vito Gannola "Green Ones Gang" Killed