When Ryan Coogler began developing his latest film “Sinners,” he knew one role would be particularly key: that of Sammie, the teenage cousin of Michael B. Jordan’s gangster twins Smoke and Stack.

Sammie is a young sharecropper and the son of a local preacher, but he dreams of becoming a blues musician, so the twins recruit him to perform at their new juke joint. There, his preternatural musical ability sets off a chain of supernatural events. It was a tricky part to cast, requiring a performer who could sing as powerfully as they deliver drama.

Coogler and casting director Francine Maisler fielded audition tapes from all over the world — some from musicians who’d never acted before, others from actors who’d never played music and everything in between. But one teenager’s tape stood out.

“He was just in the dark — like he didn’t turn his lights on.