In April 1976, the flawless Watergate film premiered in Washington – cast members and reporters share their memories of ‘the granddaddy of journalism movies’

The rustle of a notepad. The click of a pen lid. On a floral-patterned sofa sits Dustin Hoffman with long hair, big collar and a lean and hungry look. Opposite is Jane Alexander, wearing a blue button-down dress, cornered and nervous in the glow of a table lamp. In this taut, claustrophobic acting masterclass, no detail is too small.

“The makeup artists ran in because the sweat was pouring off Dustin’s face,” Alexander recalls with a laugh. “Gordon [Willis, cinematographer] said, ‘Don’t touch that, I’m lighting off his sweat!’ I love that.”

Hersh’s record on uncovering the big stories, from My Lai to Abu Ghraib, speaks for itself. This documentary watches him at work: dogged, nonconformist and combative

Renowned investigative journalist Seymour Hersh was never played in a film by Robert Redford or Dustin Hoffman, like the Washington Post’s Bob Woodward and Carl Bernstein. But as this documentary portrait argues, he’s probably more important than either. Hersh has a longer record of breaking big stories, from the My Lai massacre in Vietnam to torture by US army personnel at Abu Ghraib prison in Iraq – the latter a historic scoop underscored by the stomach-turning photos which Hersh brought to light. Hersh is asked if Abu Ghraib would have been the story it was without those pictures and replies: “No pictures, no story.” Well, maybe. But his other scoops had no pictures of this kind. One incidental thing Abu Ghraib showed was how ubiquitous digital photography became at the beginning of the century; how easy it was to take and share photos. Now, in the new era of AI, photos are ceasing to be the smoking gun of truth.

The title of this movie speaks for itself. Hersh is always on the hunt for things that powerful people would prefer to stay hidden – although a paradox of the film is that Hersh has to protect his sources, cover them up as it were. Secrecy plays a part in his own professional life, and when it appears as if film-makers Laura Poitras and Mark Obenhaus have sensitive names in the notes that he has turned over to them, Hersh becomes agitated and appears ready to back out of the documentary entirely.