Meticulous in Building His Bombs, Fastidious in Remaining At Large

From the loving way he pieces together his explosives, his choice of targets and clues about which newspaper he might read, Federal investigators have gleaned some notion of his Luddite mind, but they have been unable to predict or prevent his attacks.

The investigators say they believe they know much about the parcel bomber who has left two people dead and 23 injured since 1978. Based on a glimpse years ago, they believe they know what he looks like. From the swath he has cut across the country and the clues he has left behind, they think they know where he is from and where he has gone. They might even know his motivation: a hatred of sophisticated technology, the one apparent link among his targets.

But after more than 16 frustrating years of meticulous sifting through the biographical details of his victims and the microscopic traces his deadly devices leave behind, Federal agents have been unable to identify him. Investigators from the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco and Firearms, some of whom have spent more than a decade on the case, call him one of the cleverest villains they have ever sought.

The bomber struck again on Saturday, when a mail bomb killed Thomas J. Mosser, an advertising executive, at his home in North Caldwell, N.J.

His treacherous packages, some mailed and some just left lying around, have been convincingly disguised as books, gift boxes, cassettes, even road debris. Each has been built from scratch, avoiding the use of even the most basic components that could be bought in a hardware store, and making him all the harder to trace. Investigators say the bomber dotes on his creations, polishing each wooden element, although it will be blown to splinters.

“This individual meticulously constructs his explosive devices and is a loner,” Barry Mawn, special agent in charge of the F.B.I. office in Newark, said yesterday. Mr. Mawn said the construction of the device that killed Mr. Mosser linked it conclusively to the other bombings, but he would not elaborate.

Investigators say that one of the bomber’s signatures, the letters “FC,” stand for an obscene phrase belittling computers, but they will not say how they reached that conclusion. The letters have appeared on the surviving pieces of some of his bombs, as well as a letter he sent to The New York Times last year.

From an instance when a shadowy figure was spotted in a Salt Lake City parking lot just before a bomb went off in 1987, investigators have compiled a description of the bomber as a man in his late 30’s or early 40’s, about six feet tall, thin, with reddish-blond hair and a ruddy complexion.

Investigators say they believe that the bomber is from the Chicago area, where the first four explosions occurred, and that he later moved to Utah, and then to California, possibly Sacramento.

As an executive of Young & Rubicam, the advertising and public relations firm, Mr. Mosser at first seems not to fit into a group of targets that includes scientists, university laboratories, a computer store and an airline executive. But in the two weeks before the bomb was sent, Young & Rubicam was hired by two of the nation’s computing giants, the Digital Equipment Corporation and the Xerox Corporation.

“That, unfortunately, seems to put him in the ballpark,” said a law-enforcement official who has been involved in the investigation of previous bombings, and who spoke on condition of anonymity.

And Mr. Mosser, like three other victims of the serial bomber, had been mentioned in The New York Times. The Times published the news of his promotion to general manager on Dec. 5, just as it had published articles on Young & Rubicam being retained by Digital and Xerox. Investigators theorize that the bomber reads either The Times or another newspaper that carries articles from The Times News Service.

In 1993, shortly before a pair of bombings two days apart maimed scientists on opposite sides of the continent, the bomber sent a letter to The Times, warning of “a newsworthy event.” One victim, a Yale computer scientist, had been featured prominently in a Times article on a technology called massively parallel computing. The other, a geneticist at the University of California at San Francisco, had been quoted in an article on genetic engineering.

Both technologies figured prominently in the film “Jurassic Park,” which opened two weeks before the bombings, and investigators say they do not believe the timing was a coincidence.

Another eerie signature, the bomber’s affinity for certain dates and times of year, would seem to point to his involvement in Mr. Mosser’s death. Four of his 15 explosives have gone off in early or mid-May, and two exploded on Nov. 15, one in 1979 and the other in 1985. Mr. Mosser was killed one day short of the nine-year anniversary of the blast the killed a Sacramento, Calif., store owner, Hugh Campbell Scrutton, the only person before Mr. Mosser to be killed by one of the bombs.