Theodore "Ted" Kaczynski, also known as the "Unabomber" who is serving a life sentence for setting off 16 explosions over a 17-year period, was transferred to a North Carolina medical facility for prisoners.
U.S. Bureau of Prisons spokesperson Donald Murphy said Kaczynski, 79, was moved on December 14, to the bureau's Federal Medical Center Butner. Murphy did not specify why Kaczynski was transferred.
Kaczynski was dubbed "the Unabomber" by the FBI after he set off homemade bombs in locations across the country, mostly universities and airlines in the earlier years of his criminal acts.
He made and detonated these bombs between 1978 and 1995, killing three and injuring 23.
The manhunt for Kaczynski became the longest and most expensive in U.S. history. The FBI enlisted a task force of over 150 investigators and analysts to find him, according to the agency's website.
Investigators finally caught a break in the case when they published Kaczynski's 35,000-word essay describing the "ills of modern society" he had sent to the FBI and Kaczynski's brother David recognized the handwriting.
He was arrested in 1996 and has been serving a life sentence without possibility of parole at a federal Supermax prison in Colorado ever since.
According to the Bureau of Prisons, there are currently 771 prisoners being treated at FMC Butner. The medical facility provides services including oncology, surgery, neurodiagnostics and dialysis.

According to the prison bureau, Butner has been home to notable offenders including John Hinckley Jr., who was evaluated there after shooting President Ronald Reagan and Bernard Madoff, the architect of a massive Ponzi scheme who died at the North Carolina facility earlier this year.
The homemade bombs that Kaczynski sent by mail—including an altitude-triggered explosion on an American Airlines flight—changed the way Americans sent packages and boarded airplanes.
A 1995 threat to blow up a plane out of Los Angeles before the end of the July 4 weekend threw air travel and mail delivery into chaos. The Unabomber later claimed it was a "prank."
After his brother recognized his handwriting, authorities in April 1996 found Kaczynski outside Lincoln, Montana, in a 10-by-14-foot plywood and tarpaper cabin where he'd been living since the 1970s. It was filled with journals, a coded diary, explosive ingredients and two completed bombs.
Kaczynski hated the idea of being viewed as mentally ill and during his trial tried to fire his attorneys when they wanted to mount an insanity defense. He eventually pleaded guilty rather than let his attorneys proceed.
In his personal journals released at trial by the government at the request of the victims' families, Kaczynski described his motive as "simply personal revenge."
"I often had fantasies of killing the kind of people I hated - i.e., government officials, police, computer scientists, the rowdy type of college students who left their beer cans in the arboretum, etc., etc., etc.,″ he wrote.
Kaczynski killed computer rental store owner Hugh Scrutton, advertising executive Thomas Mosser and timber industry lobbyist Gilbert Murray. California geneticist Charles Epstein and Yale University computer expert David Gelernter were maimed by bombs two days apart in June 1993.
The Associated Press contributed to this report.
