If one of your family members were killed in a terrorist attack, and years later, you still had questions about who was responsible, what would you be willing to do to find the truth?

For author and filmmaker Ken Dornstein, whose older brother, David, was killed in the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, the answer involved conducting his own investigation — one that picked up where the official inquiry left off.

“We got part of the conspiracy, but only a small part,” Stuart Henderson, the retired lead Scottish investigator on the Lockerbie case, tells Dornstein in My Brother’s Bomber, a three-part FRONTLINE documentary about Dornstein’s search that begins tonight on PBS.

That “small part” was a Libyan man named Abdel Basset al Megrahi, the only person ever convicted for the bombing. Megrahi was sentenced to life in prison, but in 2009, dying of cancer, he was granted a compassionate release and sent home to Libya under a cloud of controversy and suspicion.

Was Megrahi — who claimed innocence until his death in 2012 — who he said he was? And who else might have been involved in planning one of the worst terror attacks on Americans before 9/11?

For Dornstein, the only way to know was to amass a list of names, travel to Libya and ask them in person — something investigators told Dornstein they could never do while Libyan leader Muammar Qaddafi was still in power.

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