In the End, a Simple Tip Breaks Unabomber Case : Massive FBI effort ends when family blows the whistle

The FBI is confident that with its arrest of Theodore J. Kaczynski it has ended the career of the elusive Unabomber, nearly 18 years after a guard was injured at Northwestern University in the first of 16 package-bomb explosions attributed to the terrorist. If the bureau is right, its most costly and challenging manhunt has finally reached fruition. The Unabomber is accused of killing three people and maiming 23 others in nine states. The victims--among them professors, an airline executive and a California Forestry Assn. official--seem to have been chosen largely at random.

The FBI’s confidence has been boosted by evidence it uncovered in the isolated cabin Kaczynski occupied in Lincoln, Mont. A partial inventory lists batteries, wires, pipes and chemicals that can be used in bomb making and diagrams relating to bomb construction. X-rays taken at the scene also show one partially assembled pipe bomb. X-ray examination is a precaution against possible booby traps.

Hundreds of thousands of hours of work have produced a wealth of physical evidence that could be used to convict the suspect. It includes fingerprints recovered from bomb residues and DNA from saliva used to affix stamps to the package bombs. But in the end, as so often happens, the big break came from a tip.

Last year the New York Times and the Washington Post reluctantly acceded to a demand from the Unabomber to publish his 35,000-word manifesto attacking the evils of industrial society, and it was distributed in copies of the Post. Several months later, family members of the suspect connected the writing style in that screed to earlier writings by Kaczynski. The family notified federal authorities, who began the surveillance that led to this week’s arrest.

The Unabomber’s manifesto records his obsessions. What awaits explanation is why he targeted specific victims and why he chose the method he did to vent his rage. A trial may clarify his motivations. Or it could reveal only the incoherent reasoning processes of a tortured mind.