The disappearance of the Lyon sisters from a mall in Montgomery County in 1975 shocked the public and mystified police. Four decades later, an overlooked tip led police to a new suspect - Lloyd Welch.Mark Bowden’s latest book, The Last Stone, describes how detectives sorted through Welch’s elaborate explanations. We hear how Bowden covered the story as a rookie reporter for the Baltimore News-American and what he thinks lies behind the popularity of the true crime genre.