Till’s story received renewed attention in the 1980s, in part because of a documentary that aired on a Chicago television station, “The Murder and the Movement.” In the years since, Till has been the subject of several books, including one by his mother, and more documentaries. In 2004, the F.B.I. reopened the investigation into Till’s case to explore whether anyone could be charged. No one was.

Last year Timothy B. Tyson, a Duke University professor and author of the 2017 book “The Blood of Emmett Till,” revealed that Ms. Donham had told him that one account she had given in front of the judge in her husband’s case — that Till had grabbed her and was menacing — was false. Some commenters on Twitter have suggested that if Mr. Cosby could be prosecuted for a sexual assault that occurred more than a decade ago, Ms. Donham should face prosecution as well.

In recent years, Till’s name has frequently been used in discussions of unarmed black men and boys shot dead by police or, in the case of Trayvon Martin, by a neighborhood watch volunteer, George Zimmerman, who ultimately was acquitted.

“It’s not just a conceptual overlap between Trayvon, Black Lives Matter and Emmett Till, but a very personal overlap,” said Dave Tell, a professor at the University of Kansas who has studied Till extensively. “The Till family is very close to the family of Trayvon Martin. They see Emmett Till as the protohistory of the Black Lives Matter movement.”