NEW YORK - The mystery of Go Set A Watchman has deepened in the weeks leading up to its much-anticipated release on July 14.

The New York Times broke the news that the "sequel" to Harper Lee's phenomenon To Kill A Mockingbird might have been discovered years earlier, in October 2011, further clouding the story of the novel's "serendipitous discovery" that set the literary world abuzz in February.

The book was said to have been discovered last August. Publisher HarperCollins and Lee's lawyer, Tonja B. Carter, have told the press that Ms Carter had set out to review an older typescript of To Kill A Mockingbird but discovered an entirely different novel instead, one with the same beloved characters but set 20 years later.

She told The New York Times: "I was so stunned."

But another conflicting narrative has come to light. Justin Caldwell, a rare books expert from auction house Sotheby's, is said to have flown to Lee's hometown of Monroeville, Alabama to meet with Ms Carter and Lee's former literary agent, Samuel Pinkus, to review documents held in a safe-deposit box.

According to the Times and the Guardian, Caldwell came across the manuscript of a novel that was, like Mockingbird, set in the fictional town of Maycomb, but with older characters. He read about 20 pages and compared these passages to a published copy of Mockingbird, and concluded that it seemed to be an early version of the celebrated novel.

Ms Carter said in a statement last week that she had, indeed, accompanied Mr Pinkus and Mr Caldwell to the bank at the behest of Alice Lee, the author's sister. But she said "she said that she was sent from the room to run an errand before any review of the materials occurred", and denied learning about the newly discovered manuscript.

Both Mr Pinkus and Sotheby's are adamant that Ms Carter was present in the room. Sotheby's said in a statement: "On October 12, 2011, Sotheby's specialist Justin Caldwell traveled to Monroeville, Alabama to look at a number of items at the request of Harper Lee's literary agent, Samuel Pinkus. Present at the meeting, which took place in the viewing room of a bank below the law offices of Barnett, Bugg, Lee & Carter, L.L.C., were Tonja Carter and Samuel Pinkus."

These widely differing accounts raise even more questions about a book that has already been shrouded in controversy.

HarperCollins has defended Ms Carter, saying that while she had not mentioned this 2011 visit, it believes her version of events leading up to the discovery of the manuscript.

Lee had said that she did not intend to publish another book after the wild success of Mockingbird. She is 89, largely deaf and visually impaired, and lives in an assisted living facility. Accusations have been fast and furious as to whether Lee was "manipulated" into publishing Watchman.

To Kill A Mockingbird was published in 1960 and became an instant bestseller, a tragic tale of the deep racial fault lines of a small town in the deep south as seen through the eyes of a child named Scout. It won the Pulitzer Prize and was adapted into an Oscar-winning film in 1962 by director Robert Mulligan, starring Gregory Peck.