September 5 director Tim Fehlbaum is opening up about why the now-Oscar contender was the next story he wanted to tell.

“It was the conversation that we — the producers, the writer and I — had with Geoffrey Mason, the real Geoffrey Mason, the character played by John Magaro,” Fehlbaum told The Hollywood Reporter at a special screening on the Paramount lot.

The film, which counts Sean Penn as one of its producers, chronicles the ABC Sports team at the 1972 Munich Olympics as they pivoted from sports reporting to live coverage of the Israeli athletes taken hostage in the Olympic Village. Peter Sarsgaard stars as legendary ABC executive Roone Arledge, while Magaro plays Mason, a young producer for the network’s Olympic coverage.

“Listening to his stories and what he experienced during this 22-hour marathon of broadcasting on this crisis situation back then in Munich,” the director continued. “That was the moment when...