The Fact of a Body is an enthralling piece of non-fiction storytelling. Alexandria Marzano-Lesnevich came face to face with a child murderer on death row during a law internship. A fierce opponent of the death penalty, she was shocked to find herself overcome by the urge to see him dead. Digging deeper into the man's case, she realized something in his story was unsettlingly familiar. Marzano-Lesnevich reveals how her experience forced her to face her own story and unearth long-buried family secrets. She talks to Val McDermid.