In Bowden’s The Last Stone (Atlantic Monthly, Apr.), detectives try to find out what happened to 13-year-old Katherine and 11-year-old Sheila Lyon, sisters who vanished from a Maryland mall in 1975.

What surprised you the most about how the case unfolded?

The duration and difficulty of the interrogation was far beyond anything I imagined, and it fascinated me. With no physical evidence and, initially, no witnesses, every bit of information about the crime had to come from the suspect himself. And the suspect, Lloyd Welch, was so compulsive a liar that his behavior bordered on comical. He also had every reason in the world not to tell the truth. Building the case against him meant traveling down a long path of deliberate untruths, stories designed to mislead. The detectives had to somehow sift the truth from a mountain of lies.

What do you think are the biggest misconceptions about how the police try to get confessions?

TV and movies have familiarized people with the real techniques of interrogation, though they continue to depict some that are illegal. Threats and coercion are still very much a part of the process, and were in this case, but they tend to be subtle and nonviolent. Questioners play upon a suspect’s fears, hopes, and options for the future, such as offering leniency in charging or sentencing, better prison conditions, and even chances for early release. Interrogators also mislead suspects, creating a false sense of the situation. The essence of skilled interrogation involves befriending the subject and persuading him that cooperation, for a variety of reasons, is in his best interests.

How was writing this different from writing Black Hawk Down?

The Last Stone is far more narrowly focused. A relatively small number of people were involved, and the events all took place within driving distance of my home. The hardest part was digesting the more than 70 hours of video and audio recordings of Welch’s prolonged interrogations. I had to immerse myself in them deeply enough so that I could experience the story alongside the detectives and Welch himself.

Why didn’t the closing of this case get much national press?

Anyone old enough in the Washington metro area immediately knows what you’re talking about if you mention the Lyon sisters. I think the reason why the story has not yet been told on the various TV true crime shows is that it strays significantly from the standard stories they tell. The only way to understand how the police obtained a conviction is to do what I did, study the hours and hours of interrogation and surveillance. When I started working on the book, those recordings were not generally available.