NEW YORK — The authors of a new J.D. Salinger biography are claiming they have cracked one of publishing’s greatest mysteries: What “The Catcher in the Rye” novelist was working on during the last half century of his life.

Starting between 2015 and 2020, a series of posthumous Salinger releases are planned, according to “Salinger,” co-written by David Shields and Shane Salerno and scheduled to be published Tuesday. The Associated Press obtained an early copy.

Salerno’s documentary on the author opens Friday.

In January, it will air on PBS as an installment of “American Masters.”

Providing by far the most detailed report of previously unreleased material, the book’s authors cite “two independent and separate sources” who they say have “documented and verified” the information.

The Salinger books would revisit “Catcher” protagonist Holden Caulfield and draw on Salinger’s World War II years and his immersion in Eastern religion. The material also would feature new stories about the Glass family of “Franny and Zooey” and other Salinger works.

No Salinger book came out after the early 1960s, as the author increasingly withdrew from public life.