it was amazing how many people thought that they knew the unabomber. >> people will say, "oh, well, it was easy. his brother told you who it was." well, what most people don't understand is, 60 other brothers told us with equal fervency that it was their brother that was the unabomber. >> phones ring constantly in the san francisco fbi's unabomb war room, some with tips, some duds. >> ninety-nine percent of the responses are false leads, unfortunately. there's only going to be one call that's going to be the right one. >> while they were waiting for a call back, david found an essay that his brother wrote decades earlier. it had an incredibly uncanny resemblance to the manifesto. >> i took it to our fbi laboratory, and i was almost immediately told that the typewriting didn't match. >> they examined it and said, "nope, it's not the typewritite. therefore, it can't be the unabomber." >> molly wouldn't give up. she called the task force directly. >> i said, "i think you're really going to want to read