MONROEVILLE, Alabama (Reuters) - "To Kill a Mockingbird" novelist Harper Lee wrote yet another book that remains unpublished, a close friend said on Tuesday, adding to the mystery surrounding the reclusive writer on the day Lee's "Go Set a Watchman" went on sale.
The unpublished book is a crime story called "The Reverend" based on a true story involving a pastor who killed three people and was acquitted of murder, said Auburn University professor Wayne Flynt, who has known Lee for more than 30 years.
"I know it exists because (Lee's) sister Louise told me," Flynt, a lecturer on Southern culture, told reporters in Lee's hometown of Monroeville, Alabama.
Flynt said he had not asked Lee about "The Reverend."
"I don't ask her anything because she needs friends in her life who just let her be," he said.
Flynt said Louise Conner, who died in 2009, told him about the book in 2003, but not who possessed the manuscript.
"Nelle might have sent it to Louise or to Alice," Flynt said, using the first name by which Lee is known among her family and close friends.
Alice Lee, a lawyer who represented her novelist sister's interests for decades, died in November 2014 at age 103.
Harper Lee, now 89, withdrew from public life a few years after the 1960 publication of "To Kill a Mockingbird," her best-selling, Pulitzer-Prize winning novel about racial injustice in the American South.
She had never published another work until the release on Tuesday of "Go Set a Watchman," an earlier draft of "Mockingbird," which has set the literary world afire.
Lee resides in an assisted-living facility in Monroeville and has declined media interviews for decades.
Tonja Carter, the lawyer who now handles Harper Lee's business affairs, could not immediately be reached for comment on Flynt's remarks.
Carter said on Monday she recently found pages of typed text and other documents in a safe-deposit box belonging to Lee that would be examined and authenticated by experts over the next few months.
Carter said she found the typed pages in the same safe-deposit box where the manuscript for "Go Set a Watchman" was discovered about a year ago.
"Something else was in the ... box. The manuscript for 'Watchman' was underneath a stack of a significant number of pages of another typed text," Carter wrote in a commentary for the Wall Street Journal.
"Was it an earlier draft of 'Watchman' or of 'Mockingbird,' or even, as early correspondence indicates it might be, a third book bridging the two? I don't know," Carter added.
Publishers Harper, a unit of HarperCollins, has ordered an initial print run of 2 million for "Watchman," and the book has been the top seller on Amazon.com for more than a week.
Reporting by Rich McKay; Editing by Jill Serjeant and Will Dunham