In papers found in his Montana cabin, Theodore Kaczynski admitted committing "non-bombing acts of violence," prosecutors said in documents filed Wednesday.
The government did not say what the acts of violence were. Justice Department spokeswoman Leesa Brown said she could not release any information. But a federal law enforcement official said the acts were serious and have never been made public.
Defense attorney Quin Denvir said the prosecution was referring to acts of vandalism that Kaczynski committed when he was much younger "which we don't feel have any place in this trial."
The government contends Kaczynski is the anti-technology terrorist known as the Unabomber who is responsible for 16 bombings over 17 years that killed three and injured 23.
Kaczynski, 55, faces trial Nov. 12 on a 10-count indictment charging him with using bombs to kill two Sacramento men and injure two others. He faces the death penalty if convicted. He also has been charged separately in New Jersey with the bombing death of an advertising executive. He has pleaded innocent to all charges.
The government filed the documents Wednesday in an attempt to use Kaczynski's writings as evidence that he was responsible for bombings he has not been charged with and that he intended to hurt people.
Such evidence could help counter a possible insanity defense. Kaczynski's lawyers have indicated they may argue that he suffered from paranoid schizophrenia.
"The defendant's decision to put his mental condition at issue makes highly relevant his admissions to committing the non-bombing acts of violence," said the brief by prosecutors Robert Cleary and Douglas Wilson.
The papers found in his cabin when he was arrested in April 1996 "contain express statements of the defendant's intent to kill and the reasons why he sought to kill," prosecutors say.
The brief said the admissions "show that his intent grew out of defendant's hatred and antisocial preoccupations."