Unabomber's Sister-In-Law Suspected Him After Reading Manifesto

"Linda saved lives," David Kaczynski said of his wife. "And, ultimately, perhaps contributed to saving Ted's life too."
8:40 | 02/11/16

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Transcript for Unabomber's Sister-In-Law Suspected Him After Reading Manifesto
He was a feared and mysterious killer known simply as the unabomber. His bombing campaign killed three and injured more than 20 people. His calling card a manifesto railing against technology in the modern world. It would be those words that led to his capture. Tonight for the first time on television, we hear from the woman who turned him in. She sat down with me for "20/20 discovery id presents homicide. The computer went off this money at Yale's computer science center -- Reporter: The most wanted in America, the unabomber, a ghost targeting universities and airliners. Thus the name. The unabomber. There's been almost as much money spent on the unabomber investigation as all serial murderers put together. He's that important. Reporter: But in the end his capture would also come down to this woman. Speaking out tonight in her first television interview. The longest FBI investigation in the history of our country. But how was it that you, a college professor, was the first to suspect Ted Kaczynski could be the unabomber? The main reason is the FBI began to release information. Reporter: More on her in a moment. Nearly 30 yes, there is ago there wasn't much information for the FBI to go on. That is until 1987 when computer store owner Gary Wright became the victim of the unabomber's 12th bomb. As I drove into the rear parking lot I noticed there was a piece of wood. I went over to pick it up. I bent down. And I put my hand on the very end of it. And immediately something happened. There was a big blast of pressure. And I was knocked about 20 feet backwards into the parking lot. What happened? When it went off there was about 200 pieces of shrapnel that went through my body at various points. Reporter: Just before Wright arrived -- I found out my secretary had been looking out this window right here. And she saw somebody kneeling down, pulled something out of a bag, and set it on the ground. And they were looking face-to-face about four feet apart from one another. Reporter: Now investigators are able to derive the first police sketches of the elusive killer, a miscellaneoustached man. A white male with high school education, might appear to be a nice guy with no apparent predisposition to violence -- Reporter: Three bombs later it's the unabomber himself who gives the FBI more to work with by contacting the media and demands two newspapers print a long manuscript he's written or the killings will continue. As we know, in inn so many cases of serial killers, pride G goeth before the fall. Reporter: The New York types and "Washington post" published the manifesto. It is blackmail pure and simple to which the "Times" and "Post" acceded. Were they justified in doing so? Reporter: History might say yes. College professor Linda Patrick reads the information the FBI releases and thinks she recognizes familiar-sounding ideas from letters her husband David Kaczynski and his family received from his brother Ted. That must have been awful to have these suspicions that you were going to share with this man, who you love -- Yes. But it was really important to talk with Dave about it. When she said, 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. Reporter: Linda's suspicions kept growing. They had posted the first few pages of the manifesto on the screen. Computer. In the lobby of the library. So Dave went with me. And then as Dave read the first page, I was sitting at his side and his jaw dropped. I thought I was going to read the first page of this, turn to Linda and say, "I told you so." On an emotional level it just sounded like my brother's voice. Reporter: David's older brother Ted had once had a promising future. He'd gone to Harvard at 16, earned a ph.d. In math at university of Michigan. But it's when Ted Kaczynski as math proper soar at Uc Berkeley he gives up on pain stream society. He build himself a cabin in Montana and retreats from the world. He began to write very hostile, angry, resentful letters to our parents. I had a hard time understanding where the resentment came from. Reporter: David and the family had long suspected Ted suffered from some kind of mental illness. But until now, David says, they had been in denial. How long do you think he was challenged with mental illness? It's pretty clear that by the time he was a graduate student at the university of Michigan, he was suffering from some pretty serious delusions. Reporter: The family makes the wrenching decision to contact the FBI. Thought about the families that were bombed. There was one in which the package arrived to the man's home and his little 2-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. So I spent those days thinking about those people. Reporter: On April 3rd, 1996, a nine-man S.W.A.T. Team apprehended Ted Kaczynski at his cabin in Lincoln, Montana. They find containers with bomb materials, notebooks containing almost 40,000 pages of writings. The typewriter on which he typed his manifesto. The FBI has arrested a man in Lincoln, Montana -- Are you the unabomber? The three of us were sitting together, Linda and myself and my mother, watching the arrest of my brother on TV. I've never seen a street person that looked worse off than Ted looked at that moment. His clothes were tattered. Apparently he had not bathed in weeks or months. I still am haunted by the look on his face. Reporter: Kaczynski goes on trial in Sacramento, California. January 1998. It's clear the key issue in the trial would not be Ted Kaczynski's guilt but his sanity and whether he would be spared the death penalty. My major argument against the death penalty for my brother is the fact that he's diagnosed with a serious mental illness. Paranoid schedulizophrenia. I would like to say our reaction to today's plea agreement is one of deep relief. Most important, my mother and I wish to reiterate to the surviving victims our deep sorrow and regret. To express our wish to reach out to you in whatever way possible -- Reporter: One of those David reaches out to is victim number 12, Gary Wright. I picked up the phone and I dialed the number. And I hear a voice on the other end saying, you've reached the Wright house at the wrong time. I wasn't prepared for that. I was like -- I mumbled, I'm David Kaczynski, I think maybe you know who I am. I'd love to talk if you're open to it, I'll try calling back in a couple of days. First he just said, I want to call and apologize on behalf of my family. That was the first thing. I said, well, David, I have to tell you something. That everybody has people in their family they probably want to apologize for and it may not be at the same level. I know people want to apologize for me and you really don't need to carry this. That's not your responsibility. What a gift. Yeah. It was like a gift. Reporter: And in ensuing years David and the man his brother tried to murder are crisscrossing the country speaking out against the death penalty, advocating instead for reconciliation, mercy, grace. I think on some level, whether we recognize it or not in ourselves, there is this hunger for reconciliation. That violence not be the last word. I don't know if Linda understands how grateful I am to her. Linda saved lives. She saved our family's honor and self-respect. And ultimately perhaps contributed to saving Ted's life too. The series "20/20 homicide" on discovery id.

This transcript has been automatically generated and may not be 100% accurate.

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