Long and Twisting Trail Led To Unabom Suspect's Arrest

The tip came the way the F.B.I. had long expected, from a family member with misgivings. But the search for the man investigators believe is the Unabomber still had months to go before the suspect was arrested on Wednesday, as his deeply torn family struggled with its loyalties and then as an elite team of agents stood vigil for weeks in the Montana snows.

And even now the case is far from finished, postal inspectors and other law-enforcement officials said today. With the arrest of Theodore J. Kaczynski in Montana, hundreds of agents, held back in recent weeks for fear of somehow tipping their hand to a fugitive who had eluded them for nearly 18 years, are now fanning out to airports, bus stations, homeless shelters and universities nationwide. They are trying to fill the many blanks in the life of Mr. Kaczynski, a Harvard-educated recluse.

The tip that led to the arrest arrived in a similarly mysterious fashion, investigators said today. When Mr. Kaczynski's brother, David, of Schenectady, N.Y., first approached the Federal Bureau of Investigation early this year, his initial contact was through an intermediary.

As described by Federal officials supervising the investigation, David Kaczynski, who had also attended Harvard and who in 1971 helped his brother buy the Montana property, grew suspicious late last year that his brother might be the author of the Unabomber's published 35,000-word manifesto.

David Kaczynski combed old family papers, finding what he feared might exist, copies of some letters dating to the 1970's that were written by his brother to newspapers protesting the abuses of technology. The sentiments were disturbingly reminiscent of what he thought he had read in the Unabomber manuscript.

But it was not until January that a lawyer for the family telephoned the F.B.I. in Washington.

"The lawyer was nervous," one official recalled. The lawyer described the situation without revealing either brother's name or the basis of the suspicions. "The brother was nervous," the official added, "wanting to protect and not to smear his brother's name if he wasn't guilty and not to hurt him if he was."

What followed was a delicate dance of persuasion. It took several more weeks to set up a meeting at an F.B.I. office with the lawyer and David Kaczynski, and just before they met, additional writings were turned over that seemed to solidify the connection.

Still, the official said, the lawyer balked at identifying the letter writer or giving his whereabouts. But agents, having established David Kaczynski's identity and schooling during the meeting, then began checking the family's background.

"We had kind of figured it out before he told us who his brother was, and that they both went to Harvard," the official said. Officials said that they had no reason to believe that David Kaczynski was in any way involved in any wrongdoing or that he was driven to come forward by the $1 million reward -- although, they added, he might be eligible to collect it.

Finally, not only did the agents discover Theodore Kaczynski's mountain cabin, but also were able to persuade his mother, Wanda, to authorize a further search of the family's house in Lombard, Ill., in mid-March as family members prepared to move out.

Quickly then, postal investigators, F.B.I. agents and explosive specialists, disguised as lumberjacks and other outdoorsmen, began slipping into Helena, and the rural hamlet of Lincoln, 50 miles northwest and not far from the cabin.

The agents began striking up conversations with local residents, hoping to learn more about the hermit in the cabin without tipping their hand. At the same time, a pair of F.B.I. snipers crept close to the cabin and staked it out for weeks, communicating with their commanders by encrypted radios.

They watched as Mr. Kaczynski sometimes emerged to tend his garden and retrieve provisions from his root cellar. But he never left his property. On Wednesday, 40 agents ended the surveillance, converging on his cabin with a search warrant. With them was an Army ordnance team, assigned to search for any booby traps, but none were found.

The officials said that Mr. Kaczysnki tried to withdraw inside the cabin, but was restrained. After his capture, Mr. Kaczynski gave no further resistance, but instead, one official said, became "quite personable, and well spoken," but asked for a lawyer. Although a psychological profile suggested he might be eager to cooperate, he declined to answer questions but engaged in pleasant small talk with the agents.

The search for the answers he declined to give is proceeding primarily on two separate tracks by agents from the F.B.I., the Bureau of Alcohol, Tobacco and Firearms and the Postal Inspection Service.

One will be a detailed examination of physical evidence investigators can uncover from Mr. Kaczynski's cabin, seeking links to the mountainous pile of bomb fragments, writings and package scraps collected over the nearly 18-year investigation into the bombing campaign.

Agents have carefully preserved and catalogued evidence from each of the bomb crime scenes, as well as the bomber's written communications to victims and news organizations, carefully analyzing the mailing labels and stamps.

The other path of inquiry will focus on building what agents call an investigative profile that could provide links in time and place between Mr. Kaczynski and the bomber known until recently only through postmarks. Agents said they had no reason, so far, to suspect anyone other than Mr. Kaczynski.

Investigators said they were examining whether Mr. Kaczynski traveled by bus in the days preceding the dates when package bombs were mailed from cities far from Montana, like Sacramento, Calif. They are also investigating whether he stayed at homeless shelters or inexpensive motels along the route.

Other agents are combing through air travel records to determine whether Mr. Kaczynski might have flown from Helena, Mont., to the cities from which the bombs were mailed. Investigators are also interviewing associates and classmates at the universities where Mr. Kaczynski studied and worked.

"We always believed there would come a day when all these many bits of information would begin to come together and that day was the day we executed the search warrant," one law-enforcement official said today.