Marja Mills, a former reporter for the Chicago Tribune, has been trying to solve the riddle of why reclusive author Harper Lee never published another book after her classic 1960 novel To Kill a Mockingbird. And now she faces a new puzzle: why Lee is denying cooperating with Mills on her upcoming work, The Mockingbird Next Door: Life with Harper Lee. Mills apparently lived next door to Harper Lee and her sister, Alice, and according to Mills’s publisher, Penguin Press, had direct access” to both.

Untrue, claims Harper Lee, who released a statement through a lawyer denying any kind of cooperation with Mills. An article in the Guardian quoted Lee:

“Contrary to recent news reports, I have not willingly participated in any book written or to be written by Marja Mills,” Lee wrote in a statement. “Neither have I authorized such a book. Any claims otherwise are false.”

Lee’s disavowal prompted Mills and her publisher to send an e-mail to the New York Times clarifying their position:

[Mills] said in an e-mail sent by her publisher that Harper Lee, known as Nelle to many of her friends, and her sister, Alice Lee, were wonderfully generous with their time and insights over the years as I researched my book.

Alice Lee signed this statement, the e-mail continued, affirming she and her sister, Nelle Harper Lee, cooperated with the project.

Tracy Locke, vice president and associate publisher at the Penguin Press, also forwarded a letter, dated March 20 and signed by Alice Lee, confirming that she and her sister had participated in, and cooperated with, the project.

Although Locke refused to comment directly on Lee’s statement, she said that it does not “trump” the letter signed by Alice.

As to the reason Lee never wrote another novel, the Guardian article also points to a 2002 interview that Mills conducted with Alice Lee, who was 91 at the time (Mills was denied access to Harper Lee herself). When asked why her sister never completed a second novel, Alice had this to say:

“I’ll put it this way,” she said. “When you have hit the pinnacle, how would you feel about writing more? Would you feel like you’re competing with yourself?” Alice also said that her sister “has not shown any interest” in writing an autobiography, instead remaining fascinated by the characters who live in rural Alabama. “We go out in every nook and cranny,” said Alice. “We explore. If a new road opens up, we try it. We have done that all our lives.”