It was May 1996, and David Kaczynski, a counselor for troubled youth in upstate New York, sat down to write a letter to his brother Ted. A month earlier, his brother had been shockingly unmasked as the shadowy Unabomber, responsible for a 17-year campaign of bombings that had killed and maimed people across the country.

Ted Kaczynski, a brilliant but mentally troubled mathematician who had retreated years earlier to a remote hovel in Montana, had been arrested based on information from a tipster to the FBI, ending one of the longest and most expensive searches in American history. He was now in custody and facing what would almost certainly be a lifetime behind bars, if not a death sentence.

The tipster was David.

“I could only imagine how much Ted resented me,” he recalled in an interview. Would Ted consider allowing him to visit, he wrote, and try to explain? “I wanted to tell him in person that we morally felt an obligation to stop the violence,” he said.

Ted declined to put David on his visitors list, and when he wrote back, it was to turn the fury of his resentment on his brother.

“You will go to hell because, for you, seeing yourself as you really are will truly be hell,” he wrote.

David remembers being stung but not surprised.

“Ted’s letter confirmed my fear and expectation,” he said. “It felt like the hand of fate falling.”

He tried again, yearning for a different response. David would spend nearly three decades writing to his brother, years marked by nostalgia, regret and intense self-reflection.

In a series of recent interviews with The New York Times, David spoke in detail for the first time about his long correspondence in an attempt to pry back open a line of communication that his decision to approach the FBI had closed.

“I was hoping that I might have an opportunity to meet with Ted and explain to him in person what I’d done and why,” David, 75, said. “I wasn’t necessarily hoping that Ted would understand my point of view well enough to forgive me. But I thought we both deserved a chance to look into each other’s eyes and share the truth of our principles and feelings.”

The Kaczynski brothers grew up in Evergreen Park, Illinois, a working-class suburb of Chicago. Their parents put a premium on intellectual curiosity, academic achievement and leading an ethically principled life.

The boys developed a love of nature. But David, seven years younger than Ted, was struck by how socially awkward his brother was and that he had no friends other than him.

Academically and professionally, the two men’s lives took off on different trajectories. Ted, a mathematics prodigy, enrolled at Harvard University at the age of 16 and then earned a master’s degree and a doctorate at the University of Michigan. From there, he became an assistant professor of mathematics at the University of California, Berkeley, but struggled with mental health issues and left after a few years. David, who aspired to be a writer, graduated from Columbia University in 1970 with a Bachelor of Arts degree in English.

The two shared a desire to escape society and seek refuge in nature. In 1971, the brothers purchased a 1.4-acre parcel of land outside Lincoln, Montana, where Ted built his new home: a shack with no running water or electricity. David was living roughly 90 miles away in Great Falls and working at a zinc smelter.

But David’s stint in Montana would soon come to an end. After losing his job at the zinc smelter in a round of layoffs, he took a position as an English teacher at a high school in the small town of Lisbon, Iowa.

David taught there for two years before taking time off to work on a novel. Describing himself as “anti-careerist,” he turned his sights on the West Texas desert, which had enchanted him since he first visited on a vacation several years earlier. David moved to the desert in 1982 and embraced an isolated and largely primitive life for extended periods over nearly eight years. In a way, he was now living in a parallel universe to Ted’s.

The bombings started May 25, 1978, when a campus security officer at Northwestern University was injured while investigating a package reported by a professor as suspicious. Over the course of Ted’s lengthy bombing campaign, three people would be killed and 23 injured by his homemade missives, all directed at what he would later say was the need to call attention to the destructive forces of industrial society.

David and the rest of the Kaczynski family had no idea that Ted’s increasing paranoia and isolation were turning violent. By around 1985, Ted had all but cut off contact with his parents, after angrily accusing them of pushing him too hard to excel academically and blaming them for making him a social misfit. He made a few exceptions: He called his mother from a pay phone in 1990 to express his condolences when his father, who had been given a terminal cancer diagnosis, committed suicide.

David had left the desert for New York the previous year to move in with Linda Patrik, an associate professor of philosophy with a personal interest in Buddhism whom he had known since junior high school. When he informed Ted of his marriage plans, Ted, who had never met Patrik, fumed and warned him that he was making the biggest mistake of his life. Ted then severed virtually all communication with him.

The Unabomber’s attacks continued, and authorities had few leads. But then, in 1995, the elusive perpetrator provided an essential clue: a 35,000-word manifesto, published in The Washington Post in collaboration with The New York Times, asserting that the world needed to understand that “the Industrial Revolution and its consequences have been a disaster for the human race.” People were living in a society that made them unhappy and then being prescribed drugs to take away their unhappiness.

David’s wife urged him to come with her to the library at the college where she taught, and he was able to read half a dozen pages of the manifesto online.

Linda told him about something that had been bothering her: Didn’t some of those phrases and ideas sound just like Ted?

Although he had scarcely admitted it even to himself, David was slowly starting to think the same thing.

For three months, David worked with a private investigator and a former FBI behavioral science expert to explore whether Ted could be the Unabomber. Finally, he reached out to a lawyer, who helped him contact the FBI.

Ted’s arrest, in April 1996, came about six weeks later, David recalled. Eventually, a plea deal averted the death penalty, resulting instead in a life sentence without the possibility of parole.

David wrote to his brother not long after the arrest and received a blistering three-page reply.

1996

You know me well enough to realize that, above all, I need physical freedom, silence and solitude and that, to me, permanent imprisonment will be a fate far worse than death. …

The real reason why you informed on me is that you hate me. …

And what you hate me for is your own gnawing sense of inferiority. Your suspicion that I was the Unabomber at last gave you your opportunity to get a crushing revenge on big brother for being smarter and more capable than you are.

David — who became a Buddhist after his brother’s arrest, finding solace in the tradition’s notion that everything is interconnected — was undeterred. Seven months after Ted’s arrest, David was still struggling with his own feelings of responsibility and apologized to him.

October 1996

I have had to glimpse my own cruelty and it is, as you say, a kind of hell. I do love you. I’m so, so sorry for what I’ve done and for how it hurts you.

Facing a brick wall when he tried to communicate with his brother, David found himself turning to an unlikely source for friendship.

Gary Wright, one of the Unabomber’s victims, was badly injured in 1987 when he picked up an odd-looking object left in the parking lot of a computer store he owned in Utah. It exploded, and his body was pierced by more than 200 pieces of shrapnel, and the nerves were severed in his left arm. He underwent a dozen operations and treatment for post-traumatic stress.

In the months after Ted’s arrest, David and his wife wrote to surviving victims and families of those who had been killed by Ted’s bombs, apologizing and asking what they could do to help them cope. The response was sparse, but later, a private investigator who had seen a TV interview with Wright, for whom David had had no address, advised David to make an effort to call him. Wright seemed approachable, the detective said, and not that angry.

David phoned Wright, and they spoke for about 20 minutes. The two men still remember their first conversation. “David, you have nothing to apologize for,” Gary told him. “You did the right thing.”

For David, it was a turning point. “It was like a bridge across this abyss between myself and all the families that had been harmed,” he said.

The two men went on to meet often through the years, making public appearances to talk about ending the death penalty and the power of friendship and forgiveness.

In 2021, David found a letter posted on Reddit that Ted had apparently written to someone whose name was scratched out, in which Ted disclosed that he was dying from terminal cancer.

2022

I can’t expect to live more than two years at the outside, and I may well be dead in less than a year.

David stepped u=p the pace of his letters to Ted.

“I needed to tell him that I loved him, and to recount the ways in which he’d had a positive influence on my life,” he said.

On a June morning in 2023, David and his wife had just finished a hike when David skimmed his cellphone. There was an email from his former lawyer, notifying him of reports that Ted had died. “I am very sorry,” it said.

Ted had been found dead in his solitary cell, having killed himself. Unbidden, David’s thoughts turned to his father’s suicide years earlier.

Even more profoundly, he felt an emptiness. All those years of letters — even without an answer, they had kept a door wedged open. Now it was closed forever.

“A totally one-sided relationship is still a relationship of sorts,” David said. “But now, if I am able to find words to describe my feelings and memories that I want to share with Ted, I can only speak those words to myself.”

David tried desperately to find out from prison officials whether he could have a role in the handling of his brother’s remains, but for weeks, he could not get an answer. He was finally told that Ted’s remains had been handled according to his written wishes and that David would have to file a federal Freedom of Information Act request to learn anything more.

It turned out that Ted had left a handwritten will.

December 2014

No person known to be related to me by blood or by marriage shall possess, or have any control over, all or any part of my estate.

David still does not know what became of Ted’s body.