The flag itself emerged around 2014 as the Blue Lives Matter movement grew in prominence. In the film, the judge recounts that he was moved during closing arguments when a prosecutor spoke of the concept behind the thin blue line. In the 1970s and ‘80s, the phrase was popularized in books and films, including the 1988 documentary, “The Thin Blue Line,” which tells the story of a man’s trial and wrongful conviction in the killing of a police officer in Dallas. Parker himself made a series of racist comments about Blacks and Latinos during his tenure, including in the midst of the 1965 Watts riots.

Under his leadership, the LAPD faced accusations of police brutality and racism as it transformed into more professionalized and militarized force that engaged in proactive policing - changes Parker viewed as necessary to ensure public safety. Parker left behind a controversial legacy. In the 1950s, Los Angeles police Chief Bill Parker picked up the term, mentioning it in speeches and adopting it as the title of a TV show he conceived to promote a polished image of the Los Angeles Police Department, which had been plagued by a history of corruption within the force. In 1992, New York police Commissioner Richard Enright used the expression as part of a public relations effort. It’s unclear when the adapted phrase was first used in police circles. The British formation became known as the Thin Red Line. The origin of the thin blue line dates back to an 1854 battle during the Crimean War, in which a British infantry regiment, in red uniforms, stood its ground against a Russian cavalry charge. Shawn Takeuchi said “over the years, the thin blue line has come to represent solidarity for law enforcement and their efforts to protect the communities they serve,” but added that the department does not take a stance on the issue.

Greg Runge, a spokesman for the department, which displays a small version of the flag on its fleet of police vehicles, called it “a symbol of solidarity and professional pride within a dangerous, difficult profession and a solemn tribute to fallen police officers and their families.” The Sheriff’s Department, which does not appear to display the flag on its fleet of vehicles or uniforms, did not respond to requests for comment.

Blue and black flag