INVESTIGATORS PUZZLE OVER HOW VICTIMS WERE CHOSEN.

Byline: Neil MacFarquhar The New York Times

Their lives could hardly have been more distant or more different. One lived in a sprawling confection of a mansion perched on its own little hillock in a sedate New Jersey cul-de-sac. He had just been promoted to general manager of one of the country's biggest advertising and public relations firms. The other inhabited a tar paper shack in the wilds of Montana with no visible means of support.

The first man, Thomas J. Mosser, died in his kitchen, killed when an innocuous-looking parcel mailed from San Francisco turned out to contain a meticulously hand-crafted bomb. The second man, Theodore John Kaczynski, is now in jail, suspected of being the Unabomber, the serial killer who assembled a chain of lethal packages, killing three people and wounding 23 since 1978.

How did the bomber single out Mosser? How did he select any of his victims? It is a mystery that confounds the targets of the bombings or their survivors, and has long stumped federal agents.

Establishing any link between the victims and the heaps of material that the FBI took from Kaczynski's cabin last week is what law enforcement officials are now trying to do.

They have been scouring his cabin in Lincoln, Mont., especially the 10 loose-leaf notebooks filled with writings and sketches. They said they hoped to come across some notation or diagram that could be tied to a specific bombing. In the next few days they expect to compare materials from the cabin with bomb fragments and other pieces of evidence recovered from the explosions.

Finding evidence that either of the two latest bombs - the one in December 1994 that killed Mosser and the one in April 1995 that killed Gilbert P. Murray, president of a California lobbying association for the timber industry - was built by Kaczynski would allow federal prosecutors to pursue the death penalty.

Of all the bomber's victims, Mosser (pronounced MOE-ser) was the only target he chose to explain publicly. But even the few lines he included in a letter last year to The New York Times did not say precisely how he came up with the name and address of the suburban New Jersey resident.

In Montana, the FBI has been questioning workers at bookstores and libraries, including the Lewis and Clark County Library in Helena, the University of Montana Library in Missoula and the library at Montana State University at Bozeman, to determine what Kaczynski obtained either on his own or by requesting it through the local library in Lincoln. And on Sunday, investigators said they had hotel records placing Kaczynski in Sacramento about the time some of the bombs carrying that city's postmark were mailed to victims.

In the bomber's April 1995 letter to the Times, he said he had blown up Mosser because he was an executive for a giant New York-based public relations firm, Burson-Marsteller. Misspelling the name, he mistakenly said Burson-Marsteller had been hired by Exxon to repair its image after the disastrous 1989 Valdez oil spill.

He also wrote that the company specialized in ``manipulating people's attitudes.'' Federal agents believe that the two manual typewriters found in Kaczynski's cabin can be tied to his manifesto and correspondence.

It is plausible that he drew the idea from something he was reading.

``Anyone who will read the anarchist and radical environmentalist journals will see that opposition to the industrial-technological system is widespread and growing,'' he states in his letter.

The myriad publications and conferences of the environmental world made something of a bogeyman out of Burson-Marsteller, especially in the year leading to Mosser's death. While exactly what the bomber read has not been pinned down, his writing seems to parallel strident environmentalist periodicals like The Earth First Journal.

Earth First is a loosely knit group of environmentalists who engaged in highly confrontational tactics against lumber and other development companies. The Feb. 2, 1994, issue of the Earth First Journal, which had been published in Missoula before moving to Eugene, Ore., in 1993, carried an attack on Burson-Marsteller for promoting industrial clients.

The article states that Exxon hired Burson-Marsteller to counter the negative publicity from the Valdez oil spill. (Although Exxon was a client, Burson-Marsteller has said it did no work for the firm on the Valdez spill.)

``It is obvious if you read the Unabomber's manifesto that there is a heavy emphasis against technology and a lot of the other things that Earth First Journal focuses on in terms of the radical end of environmental politics,'' said Jake Kreilik, campaign coordinator for the Missoula office of an environmental group called the Native Forest Network.

A month before the bomb killed Mosser, 500 environmentalists from all over the world gathered in Missoula to coordinate opposition to multinational timber firms. The town is 60 miles west of Lincoln and was a frequent transit point for Kaczynski. Conference organizers do not remember anyone fitting his description, nor were his last targets the subject of specific seminars. But Burson-Marsteller would likely have been mentioned frequently.

``People were probably mentioning it because it is the tendency among a lot of activists to know which corporations are the buzzwords of the moment,'' said Tom Fullum, who helped organize the gathering.

No matter how the bomber ultimately narrowed his target down to one person, he was evidently using dated reference material to do it. Mosser, for example, had been promoted out of Burson-Marsteller to its parent firm of Young & Rubicam in March 1994, nine months before he was killed.