The explosive opening in the first episode of HBO’s “Watchmen,” with citizens of a black Tulsa, Okla., neighborhood gunned down by white vigilantes, black businesses deliberately burned and even aerial attacks, has brought new attention to the nearly buried history of what the Oklahoma Historical Society calls “the single worst incident of racial violence in American history.”

Though it looked like something made up for the series inspired by Alan Moore’s original “Watchmen” stories for DC Comics, the Tulsa race massacre of 1921 was an all too real incident that decimated 35 city blocks, including the business district of Tulsa’s Greenwood community, which Booker T. Washington once called the “Black Wall Street of America.” The official death toll was 36, but others say that as many as 300 may have been killed; 800 were injured and more than 6,000 black citizens were interned for up to eight days. A search for mass graves has been undertaken in recent years.

The incident began with an encounter between 19-year-old Dick Rowland, a black shoeshiner, and elevator operator Sarah Page, who by some accounts was as young as 15. For reasons that are still unknown, Page screamed when Rowland entered the elevator. Police were called and Rowland was arrested for attacking Page, though later accounts say Rowland may have simply tripped and fell onto Page. An inflammatory newspaper account stirred up the white community and crowds gathered outside the courthouse.

With thoughts of protecting Roland from lynching, members of the black community also appeared but were outnumbered and retreated after fights broke out in the city’s Greenwood neighborhood, where most black businesses and homes were located. The mob followed, and the massacre began in full force, aided by the Ku Klux Klan.

“The mob torched the soul of the city, said former state Rep. Don Ross in “Tulsa Race Riot: A Report by the Oklahoma Commission to Study the Race Riot of 1921,” “an evil from which neither whites nor blacks have fully recovered.”

In the aftermath of the killings, attempts were made to cover up the events. Stories were removed from newspaper archives and some official accounts were destroyed. It took decades for historians and Oklahoma officials to unearth the history and begin to teach it in schools. But the years of silence took a toll on the truth — and even on how to label the incident. Many, for instance, question whether to call the events a “riot” or “massacre.” “Designating it a riot prevented insurance companies from having to pay benefits to the people of Greenwood whose homes and businesses were destroyed,” said a report by the Tulsa Historical Society and Museum.

High school history teacher Seymour Williams, explaining why there was largely silence in the black community following the violence, told Ross: “Blacks lost everything. They were afraid it could happen again, and there was no way to tell the story. The two Negro newspapers were bombed. [People] were too busy just trying to make it. The killers were still running loose and they’re wearing blue suits as well as Klan sheets.”