When filmmaker Ken Dornstein was 19 years old, his older brother David was one of 189 Americans killed in the bombing of Pan Am Flight 103 over Lockerbie, Scotland. Some 25 years later, only one suspect, a Libyan man, was ever convicted of the terror plot, which killed 270 people in total. He was sentenced to life in prison but later released. Who else was involved remains an open case. Who was really responsible for one of the worst terrorist attacks on Americans before 9/11? In this emotional and suspenseful three-part series, Dornstein embarks on a quest for answers -- diving deep into the case files, assembling a list of suspected plotters, and tracking them for almost five years across the Middle East and Europe.