Theodore “Ted” Kaczynski, the Harvard-educated mathematician who lived in the Montana wilderness and ran a 17-year bombing campaign that killed three people and injured 23 more, has died at age 81.

A spokesperson for the federal Bureau of Prisons says that the man branded the “Unabomber” by the F.B.I. died at the federal prison medical center in Butner, North Carolina.

Kaczynski was found unresponsive in his cell early Saturday morning and was pronounced dead around 8:00 a.m.

While a cause of death was not immediately known, Kaczynski was previously in a maximum security facility in Colorado but was moved to the North Carolina medical facility in December 2021 due to poor health.

Kaczynski admitted to committing 16 bombings between 1978 and 1995, permanently maiming several of his victims.