the way the bombs were made and sent. many contained meticulously-carved wood. some were signed with the initials fc. >> june of 1980, we had the fourth unabomb event. this time, it was a bomb mailed to percy wood, the president of united airlines. >> he sent a letter to the president of united airlines, saying, "i'm sending you a book of great social significance, and you must read it." so when he opened that package, it exploded. >> the bomb was a small cylinder placed inside a hollowed-out section of a book. >> he devised stratagems for the victims to be sure to open the device. >> the case, codenamed unabomb, has primarily involved victims who worked for universities or airlines. >> un for university and a for airliner, unabomber. >> it was the randomness of it that frightened everyone. it would seem to die down for a while, and you'd almost forget it, and then suddenly it would happen again. >> then his most vicious bombing yet, his first kill.