 The Unabomber was the target of one of the Federal Bureau of Investigation 's costliest investigations . Before Kaczynski 's identity was known , the FBI used the title " UNABOM " ( UNiversity & Airline BOMber ) to refer to his case , which resulted in the media calling him the Unabomber . The FBI ( as well as Attorney General Janet Reno ) pushed for the publication of Kaczynski 's " Manifesto " , which led to his sister @-@ in @-@ law , and then his brother , recognizing Kaczynski 's style of writing and beliefs from the manifesto , and tipping off the FBI . Kaczynski tried unsuccessfully to dismiss his court @-@ appointed lawyers because they wanted to plead insanity in order to avoid the death penalty , as Kaczynski did not believe he was insane . When it became clear that his pending trial would entail national television exposure for Kaczynski , the court entered a plea agreement , under which he pleaded guilty and was sentenced to life in prison with no possibility of parole . He has been designated a " domestic terrorist " by the FBI . Some anarcho @-@ primitivist authors , such as John Zerzan and John Moore , have come to his defense , while also holding some reservations about his actions and ideas . 
