For 17 years the 'Unabomber' reigned terror on America. His brother was his undoing.

Content warning: This post includes a mention of suicide that may be distressing to some readers.

These were the attacks that kept America on edge for 17 years.

Between 1978 and 1995, the 'Unabomber' killed three people and injured 23 more during a mass mail-bombing, terrorism spree. 

For the FBI, catching the Unabomber was one of their longest-running investigations, saying it took a team of 150 full-time investigators and analysts to find the man behind it – Theodore 'Ted' Kaczynski.

Detectives say it was a tip-off from Kaczynski's brother that was the Unabomber's ultimate undoing.

Watch the trailer for Unabomber: In his own words. Post continues below.

In 1978, the attacks began.

A passerby found a package – addressed and stamped – in a parking lot at the University of Illinois, Chicago Circle Campus. The package was returned to the person listed on the return address, Northwestern University Professor Buckley Crist, Jr. He did not recognise the package and called campus security. The package exploded upon opening and injured the security officer.

A year later, a graduate student at Northwestern University was injured when he opened a box that looked like a present. It had been left in a room used by graduate students.

Then the Unabomber extended his sights to airlines. 

In November 1979, American Airlines Flight 444 flying from Chicago to Washington, D.C., filled with smoke after a bomb detonated in the luggage compartment. Fortunately, the plane landed safely, since the bomb did not work as intended. Several passengers suffer from smoke inhalation.

The Unabomber then targeted the United Airlines President in 1980, sending him a package holding a bomb encased in a book.

There was a bomb discovered in the hallway of a building at the University of Utah in Salt Lake City in 1981.

In 1982, a bomb sent to the head of the computer science department at Vanderbilt University injured a secretary, after she opened it. And the attacks continued and continued — another in 1982, four in 1985 and one in 1987. In 1985, one of those bombing attacks killed a person.

Across 17 years, the FBI had a serious challenge on its hands. The culprit behind these attacks was building untraceable bombs and delivering them to mostly random targets that threw off authorities.

Of course, we now know who the man behind it was.

Ted Kaczynski was an American mathematician. He was Harvard educated and had been an acting assistant professor at the University of California, Berkeley, where he taught mathematics.

Then after resigning from Berkeley, Kaczynski moved to a remote cabin he had built in Montana, where he lived a simple life with little money, and no electricity or running water. 

He was strongly against advancing modern technology and industrialisation. He then took that hatred and turned it into a domestic terrorist vendetta. 

Ted Kaczynski during his time at Berkley in 1968. Image: Netflix.

Since childhood Kaczynski's brother David said he had always seen Kaczynski as having a different way of looking at things. David said his brother was incredibly "gifted" and "a genius". In terms of intelligence, Kaczynski had a very high IQ. But throughout his life, associates, family and friends have said he was a "smart but lonely individual". 

By 1993, Kaczynski had cut off all contact with his family. He was growing more and more isolated.

His brother David said that prior to the estrangement, Kaczynski had been writing "very hostile, angry, resentful letters" to their parents.

"I had a hard time understanding where the resentment came from or what justified it in his mind," David recalled.

Kaczynski's callous attacks continued. On June 22, 1993, a geneticist at the University of California was injured after opening a package that exploded in his kitchen.

Two days later, a prominent computer scientist from Yale University lost several fingers to a mailed bomb.

In December 1994, an advertising executive was killed by a package bomb sent to his New Jersey home. A second murder then occurred in April 1995, after a mailed bomb killed the president of the California Forestry Association in his Sacramento office.

In 1995, Kaczynski sent the FBI a 35,000-word essay claiming to explain his motives and views of the ills of modern society. After much debate about the wisdom of "giving in to terrorists," the FBI Director's approved the task force's recommendation to publish the essay in hopes that a reader could identify the author. The Washington Post and The New York Times reluctantly published the manifesto. 

Thousands of people suggested possible suspects. But there was one that stood out to authorities.

In 1995, David said his wife Linda Patrik read the manifesto published in the newspaper, along with the descriptions of the potential suspect from the FBI. Something immediately clicked for her.

"It was churning up in my head quite a bit. And I thought 'Gosh that sounds like Dave's brother'. For a while I was going to hold off, but then I did broach the topic," Linda recounted.

David remembers Linda coming to him saying she thought it could be Kaczynski. He wasn't immediately convinced. But when he read the first few lines of the manifesto himself, his "jaw dropped".

"I have to admit, some parts really did sound like him," David said in the Netflix docuseries Unabomber: In His Own Words. "It sounded like the way he argued, the way he talked, the way he expressed an idea."

For Linda, she felt certain it was Kaczynski. 

She recounted on ABC's 20/20: "I'd thought about the families that were bombed. There was one in which the package arrived at the man's home and his little two-year-old daughter was there. She was almost in the room when he opened the package. Luckily she left, and his wife left. And then he died. And there were others. And so I spent those days thinking about those people."

Soon afterwards, David and Linda reported Kaczynski to the FBI, saying it was done "with the heaviest of hearts".

David and Linda. Image: ABC's 20/20.

David also provided letters and documents written by his brother. The FBI's linguistic analysis determined that the author of those papers and the manifesto were almost certainly the same. 

This then gave the FBI enough evidence to gain a search warrant. There, investigators found a wealth of bomb components — 40,000 handwritten journal pages that included bomb-making experiments and descriptions of Unabomber crimes. They also found one live bomb, ready for mailing.

As for how Kaczynski got the infamous title the Unabomber, it came from the FBI's code for university and airline bombing 'UNABOMB'.

The moment David was told that his brother had been charged and was believed to be the Unabomber, he said "Thank God we did what we did [in reporting to the FBI]".

Soon after Kaczynski was arrested and charged, he asked his attorney how he had been found by investigators. The attorney told Kaczynski that it had been reported that David was the one who reported his suspicions.

"I heard this third hand," David noted, "But Ted said 'No that's not possible, David loves me. He would never do that." It was at this point Ted told his attorneys that, "he would have nothing to do with his family again."

Ahead of the trial, it was undetermined what exact mental state Kaczynski was in. Some psychiatrists determined he had paranoid schizophrenia, others said it was a misdiagnosis. He was however declared competent to stand trial.

To avoid the death penalty, Kaczynski pleaded guilty to all charges in 1998. For the rest of his life, he was in an isolated cell in a Supermax prison in Colorado. 

In December 2021, he was transferred to a federal medical centre in North Carolina, following a terminal cancer diagnosis. 

This week, prison staff discovered Kaczynski unresponsive in his cell. He was pronounced dead upon being transported to a nearby hospital. It is believed to have been suicide.

The impact of Kaczynski's crimes was wide-reaching.

Some victims lost multiple fingers, one sustained permanent hearing loss. Another bled nearly to the point of death.

Three people lost their lives.

For the general public, simply going through one's mail prompted severe anxiety for so many Americans, with the threat of explosives at the forefront of many minds.

As David said to 20/20, he's forever thankful that his wife brought up her suspicions with him about Kaczynski. 

"I don't know if Linda understands how grateful I am to her for what she did, for her courage," David said. "Linda saved lives. She saved our family's honour and self-respect and, ultimately, perhaps contributed to saving Ted's life, too."

If you think you may be experiencing depression or another mental health problem, please contact your general practitioner. If you're based in Australia, 24-hour support is available through Lifeline on 13 11 14 or beyondblue on 1300 22 4636.

Feature Image: Netflix.