It is the big mystery of what became of Harper Lee, and this is one iteration of it. I think for a lot of readers, it’s unsatisfying because I don’t put my thumb on the scale. I think a different writer would have made a guess. It’s something I really think Harper Lee would appreciate about the book, the degree to which I tried to be scrupulous.

But if you had to make a guess …

I am an optimist in general, and I’m an optimist about Harper Lee. She was an extraordinary writer and thinker, and there’s a way in which she had everything going for her with this book. Look, I did it, so of course she could have, and probably did, and there’s probably no one more excited to read whatever exists of “The Reverend” than me. I’m pretty sanguine. I think there’s potential for her to have written the whole thing. People who lived around her on the Upper East Side heard the typewriter at all hours of the day and night.

And by your account, she gathered an incredible amount of material.

It was clear she had a mind for the investigation. She had all the pieces. She should be able to write it, and then we have to sit with the question of, what happened?

Were you at all intimidated taking on a literary project that Lee had failed to complete?

I think “Mockingbird” is one of the most extraordinary novels in the English language, and the idea that the woman who wrote that couldn’t do it doesn’t bode well for the likes of Casey Cep. Imagine if you thought Harper Lee was going to tell your story, and then Casey Cep, this writer you’ve never heard of who’s never written a book, she’s not even from Alabama, I think for some of these people it was like, “We get you? We were supposed to get Harper Lee and we get you?”

I felt like there was one thing I could do which she was never going to do, which was talk about her. It’s the story behind the story. She would never have included herself.