(CNN) — Theodore “Ted” Kaczynski, the Harvard-trained math professor who unleashed a deadly bombing campaign from a shack in rural Montana and became known as the “Unabomber,” has died, according to the Federal Bureau of Prisons. He was 81.

Kaczynski was found unresponsive in his cell at the Federal Medical Center in Butner, North Carolina, around 12:25 a.m., Saturday morning, the bureau said in a statement.

“Responding staff immediately initiated life-saving measures,” the bureau said. “Staff requested emergency medical services (EMS) and life-saving efforts continued. Mr. Kaczynski was transported by EMS to a local hospital and subsequently pronounced deceased by hospital personnel.”

Kaczynski had been serving eight life sentences after he pleaded guilty in 1998 for sending mail bombs that killed three people and wounded 23 others through the mail from 1978 to 1995.

He was arrested in 1996 at a small, remote cabin in western Montana.

In 2021, Kaczynski was moved to the federal medical center in North Carolina, according to the bureau. He had been held at Supermax in Florence, Colorado, before he was transferred to FMC Butner on December 14, 2021.

Portrayed by prosecutors as a vengeful loner, Kaczynski published 30,000-word treatise that became known as the Unabomber Manifesto.

In the document, Kaczynski claimed a moral high ground for his deadly campaign, justifying the attacks in the name of preserving humanity and nature from the onslaught of technology and exploitation.

“I believe in nothing,” Kaczynski wrote. “I don’t even believe in the cult of nature-worshipers or wilderness-worshipers. (I am perfectly ready to litter in parts of the woods that are of no use to me – I often throw cans in logged-over areas.)”

A sentencing memorandum quoted extensively from Kaczynski’s journals, in which he wrote of a deep hatred of people.

Since a tip from his brother David led to Kaczynski’s arrest in April 1996, the family has claimed the writings reflected the mind of a paranoid schizophrenic, not a cold-blooded killer. A federal prison psychiatrist agreed, opening the way for prosecutors to drop their demand for the death sentence and allow a plea bargain.

Diagnosed as a paranoid schizophrenic

After an apparent suicide attempt in his jail cell before his plea, Kaczynski asked the judge to allow him to fire his attorneys and take over his own defense. He said he wanted to base his defense on his belief that technology is destroying humanity.

Kaczynski agreed to undergo tests by a federal psychiatrist, Dr. Sally Johnson, to prove he was mentally competent to defend himself.

While Johnson concluded that Kaczynski was mentally competent, she also diagnosed him as a paranoid schizophrenic.

The last-minute plea deal was struck just before his trial was to begin. Prosecutors dropped their request that Kaczynski be given the death penalty and asked that he be given life in prison without parole.

US. District Judge Garland Burrell Jr., who sentenced Kaczynski, said: “The defendant committed unspeakable and monstrous crimes for which he shows utterly no remorse.”

‘He’ll be closer to hell’

The plea bargain saved Kaczynski from a trial and possible death by lethal injection.

“Because of these vicious acts of terrorism and because of the callous nature of the crimes, Theodore Kaczynski poses a grave danger to society and should be sent to a facility where he can be closely monitored,” Burrell said.

At the sentencing hearing, Susan Mosser, who lost her husband in a Unabomber attack, urged Burrell to “make the sentence bullet-proof, or bomb-proof, lock him so far down that when he does die, he’ll be closer to hell. That’s where the devil belongs.”

Her husband, Thomas, a New Jersey advertising executive, was killed by a package bomb in 1994.

She spoke above occasional sobs in the courtroom, noting that her 15-month-old daughter Kelly had watched her father bleed after the bomb went off.

“No, no, no, not my Daddy!” the little girl had cried.

Kaczynski’s other vicrtims were computer rental store owner Hugh Scrutton and timber industry lobbyist Gilbert Murray. Geneticist Charles Epstein and computer expert David Gelernter were maimed in bombings.

“Justice has been done, and Theodore Kaczynski will never threaten anyone again,” Attorney General Janet Reno said in a statement at the time.

A prosecutor had called Kaczynski’s brother David, who provided the information that led to his brother’s arrest, “a true American hero.”

David Kaczynski, in a statement after the plea, said: “My mother and I wish to reiterate our deep sorrow and regret to the victims…(and) to reach out in whatever way possible to ease their pain and express our love.”

Ted Kaczynski had quit a tenure-track position at the University of California, Berkeley in 1969 to build a shack near Lincoln, Montana. He lived there without running water or electricity for more than 20 years.

Kaczynski waged his 17-year “anti-technology” bombing campaign from the 13-by-13 foot shack.

Along with the deaths and injuries he inflicted, Kaczynski threatened to blow up airplanes. He placed a bomb on one flight in 1979, forcing the plane to make an emergency landing when a fire broke out in the cargo hold.

At one point, Kaczynski was able to force newspapers to print his 35,000-word manifesto, which denounced technology and the destruction of the environment. Its similarity to letters he sent to his family alerted his brother, who made the decision to turn Kaczynski in.

In 1999, Kaczynski told Time magazine he “would rather get the death penalty than spend the rest of my life in prison.”

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