Ted Kaczynski, the convict known as the Unabomber, was found dead in his prison cell Saturday morning, according to multiple reports. He was 81.

Kaczynski was found dead around 8 a.m. at a federal prison in North Carolina, a Bureau of Prisons spokesperson told the Associated Press. A cause of death is uncertain.

He had been moved to the federal prison medical facility in North Carolina in December 2021 after spending two decades in a federal Supermax prison in Colorado for a series of bombings that targeted scientists.

Kaczynski was serving life without the possibility of parole following his 1996 arrest at the primitive cabin where he was living in western Montana. He pleaded guilty to setting 16 explosions that killed three people and injured 23 others in various parts of the country between 1978 and 1995.

The Associated Press contributed to this report. This is a breaking story and will be updated.