THE younger brother of Theodore “Ted” Kaczynski, 53, the suspected Unabomber, wrote to him last autumn, asking to visit him at his remote shack in Montana. Documents have now been found at the shack bearing the names of some of the Unabomber’s victims.

David Kaczynski, whose struggle with his conscience is perhaps the most intriguing aspect of the arrest of the prime suspect, wanted discreetly to check his fears that his eccentric brother was the multiple bomber.

A charity worker from New York Stale, he felt the first stirrings of suspicion last summer after noticing that his elder brother’s occasional sorties from Montana bore a similar pattern to the Unabomber’s attacks. The two brothers had not met for six years, but Ted sent postcards and letters home.

David Kaczynski’s disquiet was accentuated in October, when he noticed marked similarities between Ted’s writings and the Unabomber’s 35.000-word manifesto, which had been published in national newspaper. At this point, he asked a private investigator to look into the matter. When his request to visit the Montana shack met with a refusal, his suspicions were increased.

Much as Mr Kaczynski may curse the difficulty of the decision he had to make to put the lives of others before family ties and take his suspicions to the FBI. he won praise from Jack Levin, a leading criminologist. “We learn from an early age that you don’t turtle.” Mr Levin said. “You especially don’t tattle on family members. This brother deserves tremendous credit.”

The discovery at Mr Kaczynski ’s shack of documents hearing the names of Unabomber victims has hardened the belief of FBI agents that they have arrested the man who over 18 years conducted a bombing campaign across America” that killed three people, but so far he has been charged only with making an explosive device.