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    Heard the one about the cop who infiltrated the KKK? Read the true story behind the latest film from director Spike Lee.

    In October 1978 Ron Stallworth saw a classified advert in one of the city's daily newspapers. The ad invited readers interested in receiving information from the Ku Klux Klan to write to a PO box located in a nearby town.

    Stallworth, curiosity piqued, wrote a note to the PO box under his own name. In it he claimed to be a white man who was interested in learning more about the KKK's activities.

    Two weeks later he received a phone call from the local organizer of the Klan's Colorado Springs chapter, asking him why he wished to join.

    From these speculative beginnings sprang an audacious undercover investigation, conducted first over the phone but eventually involving face-to-face contact.

    It led to one of Stallworth's white colleagues impersonating him with such success he was invited to become leader of the Klan's local chapter.

    It also led to the exposure of white supremacists in the military, the thwarting of numerous planned cross burnings and Stallworth becoming a card-carrying member of one of America's most detested organizations.

    Most detested, yes. Brightest, no. At no point during Stallworth's investigation did his fellow Knights of the Ku Klux Klan suspect the man they were talking to over the phone and the man who was attending their meetings were not the same person.

    Stallworth eventually left Colorado to become an investigator in Utah, where he became a recognized expert in the correlation between gangster rap music and street gang culture. He retired in 2005, after which he wrote the memoir that saw him receive death threats from outraged white supremacists.

(https://www.bbc.com/news/entertainment-arts-44457873)