Twenty years after the Unabomber was arrested for sending a series of explosives through the mail, a handwritten letter has surfaced claiming he is ready to tell his story.

Ted Kaczynski, 74, sent a letter to Lawrence Wright, a writer for the New Yorker, from a supermax facility in Florence, Colorado, claiming he is 'NOT mentally ill' and wants to dispute his brother's statements.

Kaczynski's brother David notified investigators after he recognized the Unabomber's writing style in a lengthy manifesto published by national newspapers, which eventually led to his arrest in 1996.

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Ted Kaczynski sent a letter to New Yorker writer Lawrence Wright from a super-maximum security prison in Florence, Colorado, claiming he 'NOT mentally ill' and wants to dispute his brother's statements

Kaczynski killed three and injured 23 people over the course of an 18-year bombing campaign that often targeted universities and airlines. He is serving four life sentences at a supermax facility in Colorado

Kaczynski killed three and injured 23 people over the course of an 18-year bombing campaign that often targeted universities and airlines.

David helped investigators identify Ted, and recently wrote a book detailing stories about his brother as well as his personal struggle turning him in.

The Unabomber was arrested in April 1996 and avoided capital punishment after he was diagnosed with schizophrenia. He pleaded guilty to all charges and was sentenced to four life terms instead.

Kaczynski's handwritten letter, which is dated April 4, 2016, was posted on Wright's twitter on Sunday.

It read: 'I am ready to speak to someone from the media regarding my brother's recent comments and to discuss how they are being used to torment me.'

'I am only granting one interview to one person. In order to determine who will get the interview, I am asking you to write me back affirming that you understand that I am NOT mentally ill, as my brother Dave, would have you believe.'

He also urged Wright to introduce himself and explain why he should be trusted.

Wright posted a photograph of the letter with the caption: 'Thanks, Ted, you're not nuts at all.'

David Kaczynski (pictured) helped investigators identify Ted, and recently wrote a book detailing stories about his brother as well as his personal struggle turning him in

David Kaczynski (right, as a child) said his family had long-suspected that Ted (left) suffered from a mental illness, but they never addressed it openly

Ted's recent letter read: 'I am ready to speak to someone from the media regarding my brother's recent comments and to discuss how they are being used to torment me'

In an interview with ABC News in February, David's wife Linda Patrik said she was the one who first made the connection the Unabomber might be Ted after the Unabomber's manifesto was printed in the Washington Post and New York Times.

David Kaczynski said: 'When she said, "Well, I think maybe your brother's the Unabomber," I thought, "Well, this is not anything to worry about. Ted's never been violent. I've never seen him violent".

'I couldn't imagine that he would do what the Unabomber had done.'

They went to the library, where the manifesto was projected, and David said: 'I thought I was going to read the first page of this, turn to Linda and say, "See, I told you so."

'But on an emotional level, it just sounded like my brother's voice. You know, it sounded like the way he argued, the way he talked, the way he expressed an idea.'

In particular, he noticed the repeated use of the phrase 'cool-headed logicians', according to the Guardian.

The realization led to Ted's arrest in a primitive cabin 75 miles east of Missoula, Montana, where he had been living without electricity and subsisting on wild rabbits.

Ted (pictured) was known as a math prodigy and neo-Luddite who graduated from Harvard in 1962 and went on to earn a PhD before becoming an assistant professor at the University of California, Berkeley at age 26

Ted was in arrested in a primitive cabin 75 miles east of Missoula, Montana, (pictured) where he had been living without electricity and subsisting on wild rabbits

The Unabomber’s trail of destruction had baffled the FBI from its barbaric outset in 1978, when he sent his first bomb to the University of Illinois at Chicago which exploded and injured a security guard.

The bomber set off another device in the cargo hold of an American Airlines flight in 1979, injuring 12 and forcing it to make an emergency landing.

He killed computer store owner Hugh Scrutton near his shop in Sacramento in 1985 and murdered advertising executive Thomas Mosser with a bomb sent to his home in North Caldwell, New Jersey in 1994.

The bomber also killed California Forestry Association president Gilbert Murray in 1995 with a package bomb sent to his Sacramento office.

In August of that year, Mrs Patrik put the pieces together and decided to ask her husband if Ted could be responsible.