In the 1950s, “The Thin Blue Line” was the title of a briefly running television show about the Los Angeles Police Department, masterminded by the chief, William H. Parker, who took advantage of Hollywood’s proximity to make public relations a key part of his tenure. He also opened up the department’s files to the writers of “Dragnet.”
Parker was known for unambiguous racism. He said some immigrants were “not far removed from the wild tribes of Mexico” and compared black residents participating in the Watts Riots—which stemmed in part from anger over his own department’s mistreatment—to “monkeys in a zoo.”
Parker used the phrase ‘thin blue line’ constantly in his speeches. The phrase was further popularized by the novels of Joseph Wambaugh, and it typified Parker’s philosophy: having served in the military, he wanted to end corruption and professionalize the police force.
In his view, the police “protected Western civilization from communists, progressive politicians, minorities, anybody who agitated for something that didn’t fit his very narrow scheme,” said Alisa Kramer, who wrote a 2007 dissertation on Parker's tenure. "There are a lot of parallels between Parker and Trump; Parker had no understanding of the complexities of poverty and racism."
After Parker’s sudden death in 1966, the city named the police headquarters after him. The Parker Center went on to be a primary site of protests in 1992 after police were filmed beating Rodney King.
Parker’s tenure augured a bigger shift towards militarism in police departments, which came to buy military gear directly from the Department of Defense. Criminologists Don L. Kurtz and Alayna Colburn have analyzed the language police officers use in formal interviews, and argue that the “thin blue line” idea is an example of popular culture informing internal police culture, highlighting “the assumed differences between officers and citizens and further progresses an ‘us versus them’ mentality among officers.”
The phrase gained another boost with Errol Morris’s 1988 film “The Thin Blue Line,” in which a Dallas judge quotes a prosecutor describing what separates “the public from anarchy.” The title was ironic, if not sly, since the film depicted how law enforcement sent an innocent man to death row.
Over the years, officers around the country occasionally placed stickers of a blue line surrounded by black on their cars. After the ambush of Dallas officers in 2016, the flag became a common sight in yards and on bumper stickers around the city, along with “Back the Blue” and “Thank a Cop” signs. Mourners wore blue neckties and hair ribbons at the funeral service, but the fallen officers’ caskets were draped with American flags.