Kaczynski was found unresponsive in his cell at the federal prison medical center in Butner, North Carolina early in the morning, Kristie Breshears, a spokesperson for the Federal Bureau of Prisons told the Associated Press. The cause of death was not immediately known.
Kaczynski killed three Americans and injured 23 more during a 17-year spree of increasingly sophisticated bombings that began in 1978.
The FBI described Kaczynski as a "twisted genius who aspire[d] to be the perfect, anonymous killer. ... the ultimate lone wolf bomber."
He mailed or hand delivered his homemade bombs and threatened to blow up airliners. His first known attack was at a Chicago university. The "Unabomber" name was derived from the words "university" and "airline bombing."
More than 150 full-time investigators, analysts, and others were assigned to a task force to nab the elusive domestic terrorist.
In 1995, authorities caught their big break. Kaczynski sent a 35,000 word manifesto to the FBI describing his motives. The task force recommended taking the manifesto public. FBI Director Louis Freeh and Attorney General Janet Reno gave the go ahead, and the manifesto was published in the Washington Post.
That publication in the Post ultimately netted the lead they needed from David Kaczynski, the Unabomber's brother.
David Kaczynski provided letters and documents written by his brother, and a linguistic analysis determined it those documents and the Unabomber's manifesto were likely written by the same person.
Investigators at last arrested Kaczysnki at a ramshackle, 10' x 14' cabin near Lincoln, Montana (see photo below provided by the FBI). Inside the cabin, they found bomb-making materials, 40,000 journal pages, and one live bomb prepped for mailing.
After pleading guilty in 1998, Theodore "Ted" Kaczynski spent most of the rest of his life in a Supermax prison in Colorado.
He was moved to the medical facility in North Carolina in December 2021, ABC News reported.
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