Ted Kaczynski, the convicted terrorist known as the Unabomber, was found dead in his prison cell early Saturday, according to a Federal Bureau of Prisons spokesperson.
Kaczynski was found unresponsive in his cell around 12:30 a.m.
ET and transported to a local hospital where he was pronounced dead, according to the Federal Bureau of Prisons.
Kaczynski, who went nearly 20 years without being captured until his arrest in 1996, was considered America's most prolific bomber.
In this April 4, 1996 file photo, Ted Kaczynski, better known as the Unabomber, is flanked by federal agents as he is led to a car from the federal courthouse in Helena, Mont.
Kaczynski's sister-in-law, Linda Patrik, was one of the first to identify Kaczynski as the Unabomber after reading the Unabomber's writing.
Ted Kaczynski, identified as the domestic terrorist known as the Unabomber, is shown in this booking photo, April, 1996. »