The news reports at the time, in the late 1980s, were horrific. Tawana Brawley, a 15-year-old African-American girl from the New York City area, was said to have been abducted and repeatedly raped by six white men. She was found with “KKK” written across her chest, a racial epithet on her stomach and her hair smeared with feces. She was so traumatized, according to reports, that at the hospital she answered yes-or-no questions by blinking her eyes. Making the crime even more vile, if that were possible, she and her lawyers later claimed that two of the rapists were law enforcement officials.

Ms. Brawley’s spokesman was the Rev. Al Sharpton — a dapper television personality and political commentator these days, but a fiery street activist back then. At a news conference, he named suspects.

“We have the facts and the evidence that an assistant district attorney and a state trooper did this,” Mr. Sharpton said. He called Gov. Mario M. Cuomo a racist and warned that powerful state officials were complicit. When asked whether Ms. Brawley would speak with the state attorney general, Robert Abrams, Mr. Sharpton said that would be like asking someone in a concentration camp to talk to Hitler.

But, as the meticulously researched Retro Report points out this week, it was all a hoax. After seven months, 6,000 pages of testimony and 180 witnesses, a grand jury found Ms. Brawley’s story to be a lie. Neither the police officer nor the district attorney accused by Ms. Brawley and Mr. Sharpton had been involved in any way, the report concluded.