For jittery air travelers, the news was decidedly mixed. No, the jumbo jet had not suddenly disintegrated in midair from metal fatigue. But, yes, there are people out there who are capable of planting bombs aboard passenger planes to blast them -- and hundreds of innocents -- out of the sky. When Britain's Department of Transport announced last week that investigators had found "conclusive evidence of a detonating high explosive" that shattered Pan Am Flight 103 at 31,000 ft. above Scotland, killing some 270 people, two questions took on a grim priority: Who did it? And why?
Working with unusual urgency,...