11:15 AM PT -- BOP says Kaczynski was found unresponsive at the facility he was being kept at, and that life-saving measures were undertaken, unsuccessfully. He was rushed to a hospital by ambulance but was pronounced dead there. It's unclear what exactly happened to him.
Notorious domestic terrorist Ted Kaczynski, best known as the Unabomber, is dead ... according to prison officials.
The Federal Bureau of Prisons says Kaczynski was found dead Saturday morning in his cell at FMC Butner in North Carolina. So far, officials aren't saying anything about the cause of death.
Kaczynski had served most of his life sentence at Colorado supermax prison since his 1998 conviction. He was transferred to NC in 2021, so he could get better medical treatment.
ABC News first reported his death.
The Unabomber evaded law enforcement for almost 20 years, while pulling off a string of bombings, several of them deadly. For the longest time, the only image the public had of him was an FBI sketch.
Authorities finally figured out who he was when his infamous manifesto, "Industrial Society and Its Future" ... was published in 1995 in the Washington Post. Kaczynski's brother recognized the writing and went to cops.
The FBI tracked him down and arrested him the following year at a remote cabin in Montana.
Kaczynski eventually pleaded guilty to setting 16 explosions that killed 3 people and injured 23 others between 1978 and 1995.
He was 81.
Originally Published -- 10:28 AM PT