The Unabomber's 35,000-word manifesto and letters to newspapers "were all typed on the same machine," the official said. "We believe he did that intentionally as a way for us to know the communications were authentic."

Experts can trace a document to a specific typewriter by studying minute variations in the positioning and shapes of letters, which change over time as typewriters wear.

Kaczynski is being held under constant surveillance in Helena, Mont. Yesterday, Kaczynski decided he did not want a preliminary hearing or a bail hearing.

California Gov. Pete Wilson, in whose state five of the bombs killed two people, said he wants any Unabomber trial in California.

On Thursday, Kaczynski was charged with possessing bomb components. The charges made no mention of the 18-year Unabom spree, which left three dead and 23 maimed.

Federal agents have found a bomb workshop in the cabin, including a partially assembled pipe bomb, chemicals and 10 three-ring notebooks filled with meticulous notes and sketches of explosives and electrical circuitry.

In addition to continuing searches of the cabin, which they fear may be booby-trapped, federal agents are also tracking Kaczynski's travels.

"Now that we've entered the overt phase where there is no longer any concern about tipping him off, we can go to all the locations of the bombings, the sites of the mailings and the places he lived and ask about him by name," the senior federal official said. "That means motels, hotels, airlines, buses, gas stations anything where his name or a known alias might have been used."

For example, the FBI requested dates that Kaczynski stayed at the Park Hotel in downtown Helena between 1982 and 1995, owner Jack McCabe said. Kaczynski stayed at the hotel 25 times during that period, McCabe said--and four of those stays were within three weeks before or after five of the nine bombings during the period.

Kaczynski Remembered

After receiving his degree from Harvard in 1962, Kaczynski earned a Ph.D. from University of Michigan and taught briefly at the University of California at Berkeley before retreating to Montana.

The few classmates who remember Kaczynski from their Harvard days describe him as a loner.

John V. Federico '62, now a physician, says his contact with Kaczynski was "just a passing acquaintance."

Federico says he sat with Kaczynski in the Eliot House Dining Hall on occasion. "He certainly seemed to be a quiet, introspective sort of person," says Federico.

Wayne B. Persons '62, who lived in the same Eliot House seven-man suite as Kaczynski recalls that "[Kaczynski] didn't interact socially with the rest of us in that suite at all."