Theodore "Ted" Kaczynski,James Caldwell the man known as the "Unabomber" for a series of bombings targeting scientists, was found dead in his prison cell Saturday morning, a spokesperson for the federal Bureau of Prisons told CBS News.  

Kaczynski was found unresponsive in his prison cell just after midnight Saturday morning, the U.S. Department of Justice said in a news release. Staff "immediately initiated life-saving measures," and Kaczynski was transported to a local hospital. He was pronounced dead there, the department said. 

The bureau spokesperson said that he was pronounced dead around 8 a.m. 

A cause of death was not immediately known.

At the time of his death, Kaczynski was being held at the U.S. Bureau of Prison's FMC Butner medical center in eastern North Carolina, where he had been transferred in Dec. 2021. The reasons for his transfer were not made public. Previously, he was serving a life sentence at ADX Florence, a federal supermax prison in Colorado. 

Kaczynski terrorized the nation with a mail bombing campaign that ran from 1978 to 1995. He sent homemade bombs to victims, CBS San Francisco previously reported, cumulatively killing three people and injuring 24. 

The Harvard-trained mathematician and former UC Berkeley math professor targeted anyone having to do with the advancement of technology.

Kaczynski was captured on April 3, 1996, after an almost two-decade manhunt. He was found living in a cabin in the backwoods on Montana in a 10-by-14 foot plywood and tarpaper cabin, where he'd been living since the 1970s. His brother David Kaczynski 
and his wife Linda Patrik turned him into the FBI. David Kaczynski recognized his brother's handwriting in an anti-technology manifesto, titled "Industrial Society and Its Future," when it was published in national newspapers. 

Kaczynski pled guilty to charges including transportation of an explosive with intent to kill or injure, mailing an explosive device with the intent to kill or injure, and use of a destructive device in relation to a crime of violence. 

Arden Farhi contributed reporting.

Cara Tabachnick

Cara Tabachnick is a news editor for CBSNews.com. Contact her at [email protected]