Ted Kaczynski, former maths professor and "twisted genius" who came to be known as the Unabomber when he carried out a 17-year spree of mysterious bombings that killed three people and baffled the FBI, died on Saturday at the age of 81, ABC News reported.

Kaczynski, who made and sent many of the bombs while living in a primitive cabin with no running water in rural Montana, was found dead in his cell at a prison in North Carolina, ABC reported, citing the Federal Bureau of Prisons.

The Harvard University graduate, a loner since childhood, targeted academics, scientists and computer store owners and even tried to blow up a commercial airliner in a one-man terror campaign from 1978 and 1995 against what he believed were the evils of modern technology.

For years, he frustrated police who, with no solid clues to the killer's identity, dubbed his case UNABOM, for University and Airline Bombings. A breakthrough came when Kaczynski released a rambling, 35,000-word manifesto entitled "Industrial Society and Its Future" that was published in the media in September, 1995.

Kaczynski's younger brother, David, tipped off police that the author's ideas sounded like those of Ted. Agents arrested the disheveled Unabomber at his cabin in April 1996.

After rejecting his lawyers' attempts to have him plead insanity, Kaczynski pleaded guilty to all federal charges relating to the bombings in 1998 and a California court sentenced him to four life terms plus 30 years in prison.

Described by the FBI as "a twisted genius who aspires to be the perfect, anonymous killer," Kaczynski was sent to ADX Florence, a "supermax" prison in Florence, Colorado. He was transferred to the North Carolina facility in 2021, ABC reported. (Reuters)