The Los Angeles Times series on "Noir Los Angeles" profiles the Gangster Squad, an extralegal group of LAPD officers formed in 1946 to fight organized crime off the record. These real life crime fighters are obviously the prototype for James Ellroy's characters, in particular those populating the nefarious L.A. Quartet of The Black Dahlia, The Big Nowhere, L.A. Confidential and White Jazz. Delving into this 1st of 7 parts, by Paul Lieberman, one espies the attitude that would spawn Ellroy's first pangs of unrequited policeman love.
Closer to home, The LA Gangster Squad was created to fight against "Hoodlum types from Rhode Island" something we in NYC know is a problem beyond even the bounds of the Demon Dog's crazed LA fiction.