Steve Lewis: April 3, 1996. Two FBI agents and a U.S. Forest Service police officer knock on the door of a 10-by-12-foot cabin secluded in the Montana mountains.

They’re at the home of Theodore Kaczynski—the man who had become known to the world as the Unabomber.

That knock was nearly 20 years in the making: The investigation into Kaczynski had started back in 1978, after he’d left the first of his homemade explosive devices in a parking lot near the University of Illinois in Chicago.

To catch the brilliant recluse who had been disciplined about leaving few clues, the FBI had to rethink its investigative strategies, lean on the media in a new way, and turn to the public for help.

It’s been 25 years since the arrest of the man who mailed and placed 16 bombs—three of them deadly. To mark this anniversary, our host, Kristen Fletcher, revisited the case with the FBI leader who helped get those agents to that cabin door and the special agent who got inside the mind of a deadly terrorist.

I’m Steve Lewis, and this is Inside the FBI.

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Kristen Fletcher: By 1993, some people thought the Unabomber was dead.

He had placed his last bomb in February 1987 in the parking lot of a Salt Lake City computer store.

That day, an employee watched a man leave an item near some of the parked cars. The bomber noticed the woman watching him from the window, but he calmly walked away.

Minutes later, the store owner’s son pulled into the lot and picked up the item, which looked like boards with nails protruding from the top. It exploded on contact—sending him to the hospital with life-threatening injuries.

That bomb was similar to one left in the parking lot of computer store in Sacramento, California, 15 months earlier. That bomb had killed the store’s owner.

After the Salt Lake City bomb, though, six years went by—and nothing. Perhaps the Unabomber had died or simply decided to stop.

But then, on June 22, 1993, a geneticist at the University of California opened a package in his kitchen—and a bomb exploded. Two days later, a prominent computer scientist from Yale lost several fingers to another mailed bomb.

Not only was the Unabomber alive, but his campaign of violence was growing more intense.

Several months later, in the early spring of 1994, Special Agent Terry Turchie was happily sitting at a desk in the FBI’s Palo Alto office. He had a view of Stanford’s campus and a portfolio of national security investigations.

Then came an offer from FBI Headquarters that Turchie could not, in fact, refuse: Take over the UNABOM task force.

Here’s Turchie recounting that conversation:

Terry Turchie: He said, “When do you think you can be here? How quickly can you get up to San Francisco from Palo Alto?”—which was in the South Bay. So I said, “Well, Ed, I have a number of things to wrap up, of course, so how about a couple weeks?”

And he said, “How about this afternoon at about 2 or 3 o’clock?”

And that was pretty much the end of my time in Palo Alto and the beginning of my time on UNABOM. And that 45-minute drive to San Francisco that afternoon was a really long drive.

Fletcher: Turchie said some good work had already been done on the case. The Bureau had formed the UNABOM task force in 1993 to bring together all of the investigating agencies—including ATF and the Postal Inspection Service—but progress had stalled. And after nearly a year of examining the bombings—some of which were 10 or 15 years prior—many of the investigators and analysts were looking to move along.

Turchie: So, the challenge was time, and the challenge was figuring out how to keep people focused on this case when their morale was kind of starting to drop pretty considerably.

Fletcher: Turchie knew he was going to need a new approach.

But let’s start with what they did know in 1994.

First, the Unabomber was called the Unabomber because universities—that’s the U-N—and airlines—the A—were the early targets of his bombs.

Turchie recounts what he saw in the investigation, so far spanning 16 years and 14 bombs.

He begins with the first known UNABOM device.

Turchie: The May 1978 bomb was interesting because it was found at the University of Chicago Circle Campus and it had $10 in uncanceled stamps, but it was not mailed. It was just left by a car. That kind of stood out.

The third bomb was interesting because it had been placed on an airplane. Most people don’t realize that almost immediately in the Unabomber’s career, he could have brought down an airplane and killed many people. But that third bomb, which was on that plane in 1979 flying from Chicago to Washington, D.C., simply malfunctioned and didn’t work right. So that became important to us as well.

The fourth bombing was also in the Chicago area. It was mailed to the president of United Airlines at the time, Percy Wood. It was mailed to his house, and it was preceded by a letter.

By 1985, there were four bombs, and they included a mail bomb from Salt Lake to a professor James McConnell at the University of Michigan. He was a psychologist.

And like the Percy Wood bomb, this bomb was built into a hollowed-out three-ring notebook. And there was a letter, though, with the bomb—this time with the package—and it was a request of Professor McConnell to review a student’s so-called master’s thesis in a topic called the history of science.

This would become so important to us that—I didn't know it, of course, then, but as I was reading all this—that a few months later, it would become one of the discoveries that would start us off on a number of investigative projects that had to do with writing.

The fourth and final bomb, of course, in 1985, was the bomb that killed Hugh Scrutton, the owner of Rentech Computer Store in Sacramento, in December of 1985.

By 1987, he shows up again at another kind of strip mall computer store called CAAMS, only this time it’s in Salt Lake City. And once again, kind of a major UNABOM event.

The subject is seen by a witness inside the CAAMS store. And this is where the artist rendition comes from—the composite drawing showing the man in the gray hooded sweatshirt and the aviator sunglasses.

After being seen and leaving that bomb also next to a wheel of a car, the bomber dropped out of sight for six years and just kind of disappeared.

We heard nothing from him until 1993.

Fletcher: That’s when the case came alive again, with those two mailed bombs.

Turchie made some changes to the task force in consultation with the head of the FBI’s San Francisco Field Office. They were going to engage in a deep reinvestigation of each bombing—a process he knew would be long and would feel fruitless and frustrating at times.

So he asked everyone to choose another member of the task force to partner with. His thinking was that they could bounce ideas off each other and keep one another’s spirits up.

They hired an outside computer consultant to clean up and compile all the data they had into a single database. That would allow them to better review suspects referred through the tip line.

They created a document called UNABOM Known Facts, Fiction, and Theory. And during a regular cycle of meetings, they assessed and reassessed this document—adding and deleting from it as theories were developed, dismissed, and re-evaluated.

And they grew the team, often relying on new agents and other personnel who they trained on their own. Each member was included in every detail of the investigation—regardless of their role.

Turchie: Every FBI employee—not just FBI agents—every FBI employee working on this case needs to be at these meetings, and everybody’s opinion counts.

So, in other words, we were asking everyone to be highly involved in every aspect of this investigation as far as being in a position to render an opinion or give their ideas and thoughts.

Fletcher: Central to the re-investigation in Turchie’s mind was to take a fresh look at the bomber himself.

Turchie wanted an updated profile, and he felt Special Agent Kathleen Puckett—who’d been on his counterintelligence squad and was now working toward a Ph.D. in clinical psychology—was the person to do it.

Here's Kathleen Puckett on the difficulty of creating an extensive portrait of the suspect she described as the most careful serial bomber anyone had ever seen.

Kathleen Puckett: This guy left practically no way to trace back any evidence that was left at the scene—parts of the bombs, components, anything else. He was a real cipher.

The profiling unit usually has a lot of evidence at a scene to review to come up with a profile of an unknown offender. In this case, they had no latent fingerprints, no hair and fibers that led anywhere, not even—even, in some of these devices along the way, the batteries were even stripped. You couldn’t even trace the batteries back to where they were purchased or acquired. And a lot of the wood and different things looked just like junk that was picked up by the side of the road.

Fletcher: With the reinvestigation of each crime, however, the task force began to piece together more of the bomber’s background. The first device tied to the Unabomer, which had been found in that parking lot in 1978, had clearly been meant for the mail. It was addressed and stamped, and there was a mailbox not far away.

So why was it left on the ground?

It was during one of those task force meetings that Turchie threw out the idea that maybe the bomb just wouldn’t fit in the mailbox.

To test the theory, they recreated the dimensions of the device and consulted postal records on the size of the mailbox that was at the site in 1978.

Sure enough, it would not have fit.

Puckett and Turchie said that small detail—and a closer look at the other early bombings—helped the task force determine that the bomber knew the Chicago area well. They figured he may have lived there and used it as his base early in his bombing campaign.

The team also reexamined the few cover letters that had preceded or been attached to some of the bombing devices. Given the Unabomber’s caution about leaving physical evidence, those letters were a rare source of needed clues.

One mentioned a book called Ice Brothers that the team went back and read—trying to suss out what messages may have been in the text of the book. He also mentioned a somewhat obscure field of study, called the history of science, in the letter attached to another bomb. It turned out only a few universities offered the history of science as a course of study; Harvard and Princeton were among the few.

Puckett said they got another rare glimpse into the mind of the bomber when he started communicating more directly—in 1993, he sent a letter to The New York Times.

Puckett: The letter said, essentially: We are an anarchist group; we are the anarchist group FC. And, you know, by the time you receive this, something significant will have occurred.

And then what fascinated me was the statement, “If nothing goes wrong.” And I thought, “Okay, this is the caution. This is the very careful preparation. He’s older. He’s more speculative. He’s more, he's less—he's more controlled than we initially might have thought he was.”

Fletcher: Despite what he’d written, they knew the bomber was not part of a group. No group could stay that tight, that undetectable, for so many years.

As 1994 drew to a close, Turchie said the task force was making progress and was feeling more positive as the pieces came together. But then the investigation hit its low point.

In December 1994, a powerful bomb killed an advertising executive in his New Jersey home. His wife and toddler had just left the house when the bomb detonated. In April 1995, another strong device killed the president of the California Forestry Association.

Kathleen Puckett said so much of the focus of the past investigative work had been on trying to find clues by looking at the victims. Were they linked to the bomber? Were they linked to each other?

Puckett saw something else.

Puckett: None of the victims knew each other. None of them had anything in common. None of them had been to school together or had a fraternity membership or, you know, worked in business or anything like that. Very, very disparate. And we thought, you know, he’s picking these people up out things he’s reading. He's not—he doesn’t know any of these people.

Fletcher: His focus, she believed, was on the deadliness of his bombs—they had grown more sophisticated and dangerous over time.

And on his secrecy. After he was seen in 1987, he disappeared for a number of years and never placed another bomb. The rest were all sent in the mail.

He would do anything to avoid being caught.

In the summer of 1995, the Unabomber reached out to the media again, this time with an offer: Publish his writings, and he won’t bomb again.

He sent several publications a dense, long essay called Industrial Society and Its Future. His manifesto.

The question now in front of the UNABOM Task Force: Do we publish this?

The first conclusion was no—we don’t give in to terrorists. There would be no exchange of publication for a thin hope that the violence would stop.

But eventually, the UNABOM Task Force changed its mind. After consulting with FBI leadership and the attorney general’s office, they decided to ask the newspapers to publish it.

The reasons were twofold. First, Kathleen Puckett was all but certain that the promise to stop bombing was hollow. She did not believe the Unabomber would stop—or could.

Second, the manifesto, with its unique ideas and very particular phrasing, spelling, and word choices, was going to look familiar to someone. And the writing would help flesh out the other things the task force had learned and begun to push out to the public through media announcements.

Here’s Turchie again on how they focused the public’s attention after a long string of bombings.

Turchie: By now we're telling people it’s not, like, as random as it looks. The Unabomber had familiarity and a nexus. Chicago, '78 to '80. Salt Lake City, '81 to '82, maybe as late as '85. San Francisco Bay area, from '85 on. Cory Hall, UC Berkley. That’s a big factor in this. Think of all that, and now look at this composite. Look at this man in 1987 with the gray hooded sweatshirt and the aviator sunglasses.

By the time the manifesto came, the public was actually focused and compartmentalized on this message. So we had now a huge piece to add to this.

Somebody would recognize this. Because, first of all, the writings were very passionate, and it was obvious—and Kathy made a big appeal on this in one of our meetings—that there’s no question this man really believes in what he’s writing here. So, he probably held these beliefs his entire life. And so that became the basis to now put that into the mix.

Fletcher: The team hoped it was enough. That someone would put it all together.

Terry Turchie laughs as he recounts a briefing on the case he did for Attorney General Janet Reno.

She asked him, “How will you know the Unabomber when you see him from the thousands of other people you get calls on?”

To which Turchie somewhat sheepishly responded, “I think we’ll know it when we see it.”

And then he held his breath until the attorney general looked back at him and said, “I believe that, too.”

The manifesto was published as a special section within the September 19, 1995, edition of The Washington Post. Between publication date and February 1996, well over 50,000 people called the UNABOM tip line.

Only one call ended up being significant.

A lawyer representing the family of David Kaczynski called the FBI’s Washington Field Office to say his client recognized some of the writing in the manifesto. He sent an essay his client’s brother, Ted, had written. There were enough similarities in the writing to get the immediate attention of agents.

Ted Kaczynski was UNABOM suspect number 2,416.

Born in Chicago, he was a brilliant mathematician who started at Harvard at 16. He went onto get his Ph.D. and taught briefly at the University of California, Berkeley. In 1971, he bought a small piece of land in Lincoln, Montana, where he moved and began living largely off the land.

As the UNABOM task force members learned more about Kaczynski—from his family and from reviewing more of his papers and files and records—they became more and more certain they had the right guy.

But on April 3, 1996, they knocked on the door of his Montana cabin with only a search warrant. They would need more evidence to arrest him.

And there was a real fear that he was so careful, so smart, so determined to cover his tracks, that they would find no physical evidence to tie him to the crimes.

But Turchie said a quick glance into the cabin that day made it clear that the tiny space was a literal bomb-making factory.

Turchie: What was really interesting is on the shelf across the back of the cabin—and this is what struck us when we looked in there—there were these containers, and they were labeled. And one was labeled with the chemical compound for potassium chlorate. And there was sodium chloride—that had its chemical compound labeled number.

There was sugar and zinc and aluminum and lead and silver oxide—all these compounds had shown up in various UNABOM devices. All of them, according to Pat and Don, our explosives guys, could be used to make explosive mixtures.

And that wasn’t all. There were other items on the shelves that were literally bomb components. And they were in, like, Quaker oatmeal cans and things like that. But they consisted of things like pieces of metal and plastic pipe and C-cell batteries and electrical wire.

Fletcher: They arrested Kaczynski for possessing explosive materials and continued the search over the next several days.

Turchie: By the time we were finished the first 24 hours, we had to stop the search because there was a live bomb under his bed, wrapped and essentially ready to mail, except it did not have any address or indicator of where the victim might be or who the victim could be.

Fletcher: Kathleen Puckett had been right—the Unabomber did not plan to stop.

The cabin also held extensive writings that included diary entries on all of his crimes.

Turchie: There was a small manila envelope. And in that envelope there were admissions and confessions to all 16 UNABOM crimes in detail.

In some selected notes, he said: I finally was ready to begin my bombing campaign in May of 1978. I had everything ready. I did a great job. I get on the bus. I go to Illinois. I cover myself. Nobody knows I’m there. I get out there and my bomb doesn’t fit in the mailbox.

Fletcher: Theodore Kaczynski eventually agreed to plead guilty to all charges. As of this recording, he is 78 years old, serving life in prison with no possibility of parole.

It was a long road, but the work Turchie and his task force did paid off—and with the help of an aware and informed public, they stopped a killer.

Turchie: And that is the lesson, really, that came out of UNABOM. The way that we organized, and the fact that we never gave up.

Fletcher: To learn more about the case, visit fbi.gov/unabomber. We have a video of a reconstruction of the Unabomber’s cabin and more details on the case.

Also, be sure to listen to part two of this series as we dig into how the UNABOM case has affected the FBI’s counterterrorism work, what the terrorism threat looks like today, and how the FBI is working to prevent future attacks.

Special thanks to Terry Turchie—the former deputy assistant director of the FBI Counterterrorism Division—and Kathleen Puckett, who was a founding member of the FBI National Security Division’s Behavioral Analysis Program. Both are now retired from the FBI.

This has been a production of Inside the FBI. I’m Kristen Fletcher with the Office of Public Affairs. Thanks for listening.