 One of Kaczynski 's tactics was leaving false clues in every bomb . He would make them hard to find deliberately to mislead investigators into thinking they had a clue . The first clue was a metal plate stamped with the initials " FC " hidden somewhere ( usually in the pipe end cap ) in every bomb . One false clue he left was a note in a bomb that did not detonate which reads " Wu — It works ! I told you it would — RV " . A more obvious clue was the Eugene O 'Neill $ 1 stamps used to send his boxes . One of his bombs was sent embedded in a copy of Sloan Wilson 's novel Ice Brothers . 
