Ted Kaczynski carried out a 17-year bombing campaign that killed three people and injured 23 others.
Kaczynski was suffering from late-stage cancer and was found unresponsive in his cell on Saturday.
He died by suicide, four people familiar with the matter told The Associated Press.
They were not authorized to discuss Kaczynski's death publicly and spoke to the AP on condition of anonymity.
Bernie Madoff, the infamous mastermind of the largest-ever Ponzi scheme, died at the facility of natural causes the same year.
Persons:
Ted Kaczynski, Kaczynski, —, Jeffrey Epstein, Bernie Madoff, David, Linda Patrik, He's, Daryl Johnson
Organizations:
Associated Press, Service, Federal Medical Center, AP, Prisons, Harvard, Yale University, The New York Times, Washington Post, FBI, American Airlines, New Lines Institute
Locations:
Butner , North Carolina, Florence , Colorado, North Carolina, Montana, California, Lincoln , Montana, Chicago