Ted Kaczynski, known as the “Unabomber,” who carried out a 17-year bombing campaign that killed three people and injured 23 others, died by suicide, four people familiar with the matter told The Associated Press.

Kaczynski, who was 81 and suffering from late-stage cancer, was found unresponsive in his cell at the Federal Medical Center in Butner, North Carolina around 12:30 a.m. on Saturday.

Emergency responders performed CPR and revived him before he was transported to a hospital, where he was pronounced dead later Saturday morning, the people told the AP.