Ted Kaczynski, also known as the Unabomber for his numerous bomb attacks, died in prison on Saturday, the Federal Bureau of Prisons told the Associated Press and ABC in the US.

Kaczynski killed three people and injured 23 more after mailing or personally delivering explosive devices, mainly targeting scientists.

He was arrested at his primitive cabin home in 1996 — following an almost two-decade hunt. He was serving a life sentence without the possibility of parole.

He had been held in a maximum security prison in Colorado until 2021 when he was moved to a prison medical facility in North Carolina. Officials did not give a cause of death on Saturday.

Kaczynski admitted in 1998 to sending 16 bombs in a reign of terror that lasted from 1978 to 1995. 

Who was the Unabomber?

He was dubbed the "Unabomber" by the FBI, with "Unabomb" a reference to the series university and airline bombings for which investigators had no leads. His meticulous care not to leave any traces hindered his capture, allowing him to continue his campaign which eventually changed the way the US postal service works and how Americans board planes.

It wasn't until he forced major US newspapers The Washington Post and The New York Times to publish his 35,000-word manifesto titled "Industrial Society and Its Future," that authorities were able to track him down.

His brother David Kaczynski recognized the tone of the text and informed the FBI. Police were then able to track down his 10-by-14-foot (3-by-4-meter) cabin in Montana where they found journals, a coded diary, ingredients for more explosives and two bombs that were ready to be sent out.

This brought the end to the longest and costliest manhunt in US history.

Kaczynski rejected the idea of presenting an insanity defense and tried to fire his lawyers who put it forward. When that failed he attempted to hang himself. He eventually pleaded guilty to prevent the insanity plea.

He was also recognized as a gifted individual, having attended Harvard University at the age of 16, skipping two grades. He also had papers published in prestigious mathematics journals.

ab/msh (AP, Reuters)