Felix Hall joined the Army in 1940, just as the United States was emerging from the Great Depression and on the verge of deploying millions of troops to fight in World War II.

Private Hall, a Black teenager from Alabama, was stationed at Fort Benning, a segregated base just across the state line in Georgia. But instead of fighting overseas, he lost his life on American soil. He was hanged at Fort Benning in February 1941, when he was 19.

This month — more than eight decades after Private Hall’s death — a plaque at Fort Benning was dedicated in his memory. But major details about his death remain unclear. Officials have been accused of failing to fully investigate what happened, and no one was ever charged.

“The sad thing to me is that this was 80 years ago, but things like that are still happening today,” said Nancy Cooks, Private Hall’s first cousin, who was a baby when he died.

Representative Sanford D. Bishop Jr., a Georgia Democrat, said efforts to erect the plaque began last year amid widespread protests against racism after the police killing of George Floyd in Minneapolis. Mr. Bishop said that he and a former staff member, Lauren Hughes, dug into what happened to Private Hall after a constituent asked about it. They ultimately worked with Army officials to unveil the marker at Fort Benning in a ceremony on Aug. 3.

“It is important that more people know about Pvt. Hall, and that his lynching was investigated by the F.B.I.,” Mr. Bishop said in a statement. “But the perpetrators were never brought to justice.”

There was another new development this month — new, at least, to modern researchers, who had seen gruesome photographs of Private Hall’s body but never his face. A local historian who had been interested in the case for years revisited old news clippings and found a photograph of the young soldier in a 1941 newspaper.

The historian, Dave Gillarm Jr., had searched for photographs of the private in military documents and newspapers that had been published during his life. But just hours after the ceremony at Fort Benning, it occurred to him that news outlets would have been far more likely to publish photographs of Private Hall after he was found dead in March 1941.

“When he was lynched, it became national news,” Mr. Gillarm said. “So I had to shift and start looking for him after he died.”