Unabomber Ted Kaczynski found dead in prison cell

Ted Kaczynski, the terrorist whose deadly bombing spree sparked one of the longest FBI manhunts in US history, has died.

Ted Kaczynski, the Harvard-educated mathematician turned terrorist known as the Unabomber, has died at the age of 81.

Kaczynski killed three people and injured 23 more during a mass mail-bombing spree between 1978 and 1995.

He later retreated to a dingy shack in Montana before his brother and sister-in-law dobbed him in to authorities, ending his campaign of terror and America’s longest manhunt.

Ted Kaczynski is flanked by federal agents as he is led to a car from the federal courthouse in Helena, Montana in April 1996. Picture: AP

He died at the federal prison medical centre in Butner, North Carolina, said Kristie Breshears, a spokesperson for the federal Bureau of Prisons.

The killer was found unresponsive in his cell early on Saturday morning, local time, and was pronounced dead, she said.

The convicted killer after being given three consecutive life sentences in 1998.

The dingy mountain cabin in Montana where FBI agents found Ted Kaczynski.

Kaczynski’s violent campaign left a number of his victims permanently maimed and changed the way Americans posted letters.

His crimes were uncovered after he forced the Washington Post and the New York Times to publish his 35,000-word manifesto, a rant againt modern life called Industrial Society and Its Future, in September 1995.

The former professor’s campaign left a number of his victims permanently maimed. Picture: AP

A 1959 photo shows Kaczynski as a Harvard University freshman. Picture: AP Photo/Harvard University

They agreed to print the manifesto on the recommendation of the FBI after Kaczynski said he would end his campaign if a national paper published his treatise.

After reading the papers, Kaczynski’s brother and sister-in-law recognised the tone and alerted the FBI, who had been searching for him for years in the nation’s longest manhunt.

The brother and mother of the Unabomber at the time of his capture.

A fictionalised account of the FBI’s lengthy search was portrayed in the 2017 series Manhunt: Unabomber, starring Aussie actor Sam Worthington.

In April 1996 authorities finally caught up with him in a 3-by-4-metre plywood and tarpaper cabin outside Lincoln, Montana.

Sam Worthington as Jim Fitzgerald in Manhunt: Unabomber. Picture: Supplied/Discovery Channel

The hut was filled with journals, a coded diary, explosives and two completed bombs.

Kaczynski’s first attacks targeted Northwestern University in Illinois in two bombings carried out almost a year apart on May 25, 1978 and May 9, 1979, injuring two people.

In November 1979, an altitude-triggered bomb he had mailed went off aboard an American Airlines flight. Twelve people suffered from smoke inhalation.

The early attacks earned him the title Unabomber from the FBI, as his targets seemed to be universities and airlines.

Over the following years he attacked a further 13 times, killing three people.

FBI agents chillingly described him as “a twisted genius who aspires to be the perfect, anonymous killer”.