Theodore “Ted” Kaczynski, known as ‘Unabomber, died in a federal prison medical center in Butner, North Carolina on Saturday. He was 81.

Kaczynski was found unresponsive around Saturday midnight. He was taken to the hospital, the Bureau of Prisons said. However, he was pronounced dead at about 8 AM, Kristie Breshears, a spokesperson for the Bureau of Prisons told USA TODAY.

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While a cause of death was not immediately known, several social media users suspected he was killed.

“America lost another real one today. We will miss Ted Kaczynski, so called “Unabomber”, as he goes to meet Jesus. A true American hero poisoned by the CIA and persecuted and vilified by the public. RIP Teddy. 🙏” a Twitter user said.

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“possible this is cleanup? We saw Epstein Whitney Bulger last week one other &now Kaczynski,” another one added.

He was serving a life sentence after sending a series of homemade bombs by mail around the country. He pleaded guilty to setting 16 explosions that killed three people and injured 23 others.

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New York Times, quoting multiple sources, reported that Kaczynski might have committed suicide. The report, however, did not specify the method.

The Harvard and UC-Berkeley educated mathematician before getting into the hermit life in a Montana cabin, was in a maximum security prison in Colorado. He was taken to a medical facility in North Carolina in December 2021 due to ill health.

Kaczynski left the first explosive in 1978 at a university in Chicago.