Ted Kaczynski, known as the 'Unabomber,' has died in prison at age 81

U.S. Marshals prepare to take Theodore Kaczynski down the steps at the federal courthouse to a waiting vehicle on June 21, 1996, in Helena, Mont. A spokesperson for the Bureau of Prisons told The Associated Press on Saturday that Kaczynski, known as the "Unabomber," has died in federal prison. (Elaine Thompson/AP)

WASHINGTON — Theodore "Ted" Kaczynski, the Harvard-educated mathematician who retreated to a dingy shack in the Montana wilderness and ran a 17-year bombing campaign that killed three people and injured 23 others, died Saturday. He was 81.

Branded the "Unabomber" by the FBI, Kaczynski died at the federal prison medical center in Butner, North Carolina, Kristie Breshears, a spokesperson for the federal Bureau of Prisons, told The Associated Press. He was found unresponsive in his cell early Saturday morning and was pronounced dead around 8 a.m., she said. A cause of death was not immediately known.