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ROME — Martin Scorsese and Leonardo DiCaprio are developing a film adaptation of true-crime thriller “Killers of the Flower Moon: The Osage Murders and the Birth of the FBI” as the director’s next project after “The Irishman.”

Scorsese’s longtime production designer, Dante Ferretti, told Variety that Scorsese hoped to start shooting “Flower Moon” in the spring of next year. The project is based on the bestselling book by David Grann, a staff writer for the New Yorker and author of “The Lost City of Z.”

Rights to “Flower Moon” were snapped up by Imperative last year for a reported $5 million, and a script has reportedly been drafted by veteran Oscar-winning scribe Eric Roth (“Forrest Gump,” “The Curious Case of Benjamin Button”).

Ferretti, who has worked with Scorsese on nine movies from “The Age of Innocence” through “Silence,” said he was going to “go to Oklahoma” to do preliminary location scouting for “Flower Moon.” The story, set in the 1920s, focuses on a string of murders of members of the Osage nation in Oklahoma after oil was discovered beneath their land. The chilling series of slayings was one of the fledgling FBI’s first major homicide investigations.

Scorsese and DiCaprio have been eyeing the project for months, and are developing it together with Dan Friedkin and Bradley Thomas, co-founders of Imperative Entertainment.

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John Atwood, Imperative’s chief financial officer, said in an e-mail that “we are currently conducting preliminary research on the film, but there are no formal attachments nor confirmed start date at this time.”

Ferretti said that “the whole 1920s world of the Indians who lived there needs to be reconstructed” for “Flower Moon,” adding that he expects to “start preparing this film in September, because Scorsese will shoot it immediately after finishing ‘The Irishman.’”

Scorsese is currently getting ready for an early September shoot on “The Irishman,” a gangster movie centered on the life of mob hit-man Frank “The Irishman” Sheeran, played by Robert De Niro. Several sources have confirmed that “The Irishman” will be financed by Netflix, though the deal has yet to be officially announced.

There is no word whether Netflix would give “The Irishman” a wide theatrical release, but “I don’t think Martin would accept the fact that one of his movies would just be seen on a small screen and not in movie theaters,” said Ferretti, who is not working on the film.

The triple-Oscar-winning production designer recently completed work on his first rock musical, “Divo Nerone,” staged in a unique open-air venue atop the Palatine Hill in the ancient Roman Forum, with a rotating proscenium and 28 scene changes. Although the show was mostly panned by Italian media and has been temporarily shut down after nuns in a nearby monastery complained about its high decibel levels, Ferretti noted that “critics praised the set design and costumes,” which were created by his wife and working partner, Francesca Lo Schiavo. The pair was recently honored by the American Academy in Rome with its McKim Medal.

Ferretti and Lo Schiavo also recently designed the set for Mozart’s “Don Giovanni,” which opened the Spoleto Festival in June – “my third opera there in three consecutive years,” he said.