Director David Lowery was puzzled by actor John David Washington's keen interest in a "tiny part" in his new Robert Redford movie The Old Man & the Gun.

The BlacKkKlansman star had his agent chase down the chance to audition for the small supporting role as a police officer, and Lowery couldn't figure out why Denzel Washington's son would be so interested in the gig.

"When I heard from his agent that he was interested in reading for a part in the film, I'll admit that I was surprised - it's a tiny part, just a few moments in a large ensemble," the filmmaker told IndieWire.

"I didn't think that anyone would want to play it, but he was excited about taking a crack at it. I really liked his energy, but even more than that, I admired his enthusiasm."

John easily won the job, and was as dedicated to nailing the part, no matter how small.

"I was very clear that it was a tiny role and there would be many scenes where he might feel like there was nothing much to do, or where he'd be in the scene but largely offscreen," recalled Lowery.

"He got it, and here's what he did with those scenes: without saying a word, he played them as if they were a close-up. He'd be deep in the set, flipping through a police file or listening to some other character rattle on about something. He doesn't distract from the primary action, but if you pay attention to him, you see an actor doing good work."

Even when he didn't have any scenes to film, John, 34, showed up to the set to study the art of filmmaking.

"He would be there on his days off, just sitting back on the set and watching," Lowery said. "That sort of spirit is all too rare."

The Old Man & the Gun, based on the real-life story of career criminal and prison escape artist Forrest Tucker, also stars Casey Affleck, Sissy Spacek, Danny Glover, and Elisabeth Moss, and is set for release next month (Sep18).