The FBI's Six Year Long Sabbatical

Following this 1987 bomb, there is a six year long break where nothing happens. The FBI continue to have not a single idea of being weird. So what's going on? I think it's clear that the post office was closer to solving this because he's ready to hand deliver them. He never hand delivers anything again. It's all through the mail. Unfortunately, after he got spotted, you got sketched out. You got, hey, told you he'd get back to the Titanic. I never grew out of that phase. I hate it.