Mark David Chapman shot John Lennon outside the Dakota, his apartment building on Manhattan's Upper West Side, on December 8, 1980, and this Frontline report tries to explain who Chapman was before that night. It traces his path from a troubled childhood and stints as a security guard and camp counselor through the religious fixations and breakdowns that preceded the shooting, using interviews with people who knew him and journalists who covered the case. The film sits with the unsettling gap between the ordinariness of Chapman's early biography and the act that made him infamous, rather than offering a tidy diagnosis. It also looks at Lennon's final months, the fame that made him reachable enough for a stranger to approach him with a book to sign hours before the killing. The report stays close to the historical record rather than speculation, treating the case as a study of an assassin's psychology as much as a crime story.