He's accused of making the bomb that ripped through the Pan Am 747 on Dec. 21, 1988. The flight from London to New York exploded over Lockerbie, Scotland shortly after takeoff. All 259 people on board -- many of whom were flying home for Christmas -- were killed, along with 11 more on the ground.
In court docs, the feds call Mas'ud an expert bombmaker who started working in a Libyan intelligence group way back in the 70s.
After 34 years, it's pretty amazing how authorities connected Mas'ud to the Pan Am bombing. According to court docs, a piece of the bomb recovered from the crash site had a shirt wrapped around it. That material was eventually traced to the island of Malta ... where authorities know he and 2 other men built the bomb that was eventually placed on flight 103.