Ms. Dahlberg, now 70, said she was happy when he took over. “I couldn’t get from her what he could,” she said by phone from her summer house on the Swedish island of Faro. “He wanted very much to show his own background, to show her.”

The Carmichael footage, which was broadcast in Sweden that year, offered an affable, intimate contrast to the furious pundit usually seen in the American news media. But for the next 40 years it sat forgotten in the basement archives the network shared with the Swedish Radio Corporation, along with other broadcasts about the movement produced around that time.

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Goran Hugo Olsson, director of the documentary "The Black Power Mixtape 1967-1975."

 

Then, around 2007, Goran Hugo Olsson, a documentary filmmaker, stumbled upon the 16-millimeter material as he looked for footage for a project about the Philadelphia soul singer Billy Paul (“Me and Mrs. Jones”). The trove included interviews with members of the Black Panther Party and a candid conversation with Angela Davis in a California jail. “I immediately realized that these images couldn’t stay in this basement,” Mr. Olsson, 45, said during a recent visit to New York. “It was my duty to put them out for a new audience.”

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Dr. Martin Luther King Jr. and Harry Belafonte, interviewed in Stockholm in 1967.

 

Using material from some 20 different Swedish television productions, he conceived the backbone of a feature-length documentary eventually titled “The Black Power Mixtape 1967-1975,” which opens in New York on Sept. 9. The movie also contains new audio interviews with veterans of the movement, including Ms. Davis, as well as younger artists and activists inspired by it, like the rapper Talib Kweli.

Mr. Olsson called the documentary “a new way of telling a story that has been put on hold for some time and needed a fresh look,” citing a contrast between the American coverage of black power and the Swedish reportage he watched on television in the ’70s. “In America it was always connected to court trials or crime,” he said, compared with the gregarious, somewhat insular tone of Swedish coverage, which he called “the Eskimo perspective.”

Hoping to lure American producers, Mr. Olsson traveled to New York and showed up at the offices of Louverture Films without an appointment. There he encountered the producer Joslyn Barnes, who was skeptical of the idea. “Here’s this tall, blond Swede saying he wants to make a film about the black power movement,” Ms. Barnes said. “I blinked at him.” Then Mr. Olsson showed her the footage of Carmichael. “It was a much more rounded view of these people as individuals,” she said. Ms. Barnes called her producing partner, the actor and activist Danny Glover. “The breadth of it was incredible,” he said of the footage. “There was a great deal of openness to the movement. You could find the voices of all these leaders outside of just snippets of what they would say to form a certain attitude.”

The documentary reflects a trend in black studies scholarship. “What we’re seeing is really a re-evaluation of the black power period,” said Peniel Joseph, a professor at Tufts University and the author of “Waiting ’Til the Midnight Hour: A Narrative History of Black Power in America,” from 2006.

“There are striking juxtapositions between the documentary image of black power and our popular memory of it,” which he described as an “emotionally charged and destructive movement.” According to Ms. Dahlberg many Swedish journalists were motivated less by the racial politics than the views they shared with its leaders in opposition to the Vietnam War. They also connected with their subjects partly by maintaining a certain cultural distance lacking in their American counterparts. Mr. Olsson followed their lead when gathering new interviews. “If you have this Eskimo perspective, people are really friendly and generous,” he said.

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Kathleen Cleaver in Algeria in 1969.

 

Many veterans of the movement see the period of activism depicted in the film validated by its continued relevance. “Because the past is filled with unresolved conflicts, it keeps people’s attention,” said Kathleen Cleaver, a law professor in Atlanta who was the communications secretary for the Black Panther Party. (She was married to Eldridge Cleaver, a party leader, who died in 1998.) She is also one of the documentary’s modern-day interview subjects. “We did things specifically to get media attention to convey our views, “ she added. “Now it’s in museums.”

According to Dr. Joseph, the resurgence of black power iconography in ’80s hip-hop stimulated a new generation of interest in the movement, which continues to mature in the academic world. “Black power is slowly being humanized,” he said.

After the movie earned acclaim at the Sundance Film Festival in January, Mr. Olsson and his producers made plans to continue its life off screen. Next spring, Haymarket Books will publish a collection of extended transcripts of the interviews Mr. Olsson conducted for the film. And Mr. Olsson has collaborated with the SoHo gallery Third Streaming for a photography exhibition opening the same day as the documentary that will showcase stills from the era and additional footage not included in the film.

Thirty years after Ms. Dahlberg interviewed Carmichael, she received a call from him as he prepared to travel to Cuba for cancer treatment. (He died in Guinea in 1998.) It was the first time the activist, now using the name Kwame Ture, had contacted her directly since their earlier time together. Reflecting on the changing times, “we laughed and laughed,” Ms. Dahlberg said, but she detected resignation in Carmichael’s voice. “He didn’t have much hope,” she recalled about his illness. “I found it to be a goodbye call. It was clear he hadn’t forgotten me.”