Experts at the FBI spent Friday examining the lengthy manifesto written by the self-described anarchist who has engaged in a 17-year campaign of mail bombings.
The man, suspected of having mailed 16 bombs that killed three people and injured 23, disrupted airline flights and mail delivery in California this week by threatening to blow up an airplane.
He later said the threat was a prank intended to draw attention to his credo, expressed in a 62-page, single-spaced manuscript mailed to the New York Times and the Washington Post.
Despite the opportunity for new insight into the bomber's thinking, investigators made no new public disclosures Friday.
The bomber said in the letter that he wanted his long manifesto _ which would take up up seven full newspaper pages _ printed in its entirety this summer by the Times or the Post, or he would resume his attacks.
Many journalists urged rejection of the ultimatum.
"If the Unabomber succeeds in commanding seven pages of the New York Times with a dreary, turgid manuscript, that is a signal to like-minded people elsewhere that they might do the same thing," said Everette Dennis, executive director of the Freedom Forum Media Studies Center in New York.
Representatives of both papers withheld decisions until authorities were fully consulted.
"We're weighing the possibility of risking human life against a publishing decision that could well encourage other acts of this kind," said Gene Roberts, the Times' managing editor. "It seems to me that you don't rush into this thing."
The Post issued a similar statement.
The unknown subject of their search is strongly believed to be a white male in his late 30s or early 40s living in or near Sacramento, Calif.
His early attacks focused on universities and airlines _ which led investigators to give the case the code name Unabom _ but in recent years he has included scientists, lobbyists and corporations among his targets.
He is, by his own word, an anarchist disgusted with modern life and determined to focus public attention on high technology and its potential for harm.
The letter sent to the Times used the return address of Calgene Inc., a company best known for making genetically engineered tomatoes, a spokeswoman for the firm acknowledged.
The company has offices in Davis, Calif., a city 15 miles west of Sacramento that is home to a branch of the University of California.
The suspect mailed two bombs in 1993 in packages with the return address of Sacramento State University.
Two of the three men killed by his bombs were in Sacramento. The last was a timber industry lobbyist, Gilbert Murray, killed in his office by an exploding package on April 24.
After two months of silence, the bomber re-emerged three days ago with a threat to blow up a commercial airliner leaving Los Angeles International Airport. Then, on Wednesday, a letter to the New York Times said the threat was a hoax, intended to regain public attention.
"Since the public has a short memory we decided to play one last prank to remind them who we are," the letter said. "But no, we haven't tried to plant a bomb on an airline (recently)."
Jim Freeman, the special agent in charge of the FBI's San Francisco office, appeared to encourage further communication with the man.
"I'd much rather see communication than bombs," he said. "We're looking to any means that would mitigate harm to the public safety."
Bob Guccione, the publisher of Penthouse magazine, said a package containing the bomber's manuscript and a letter arrived Thursday at the magazine's New York offices.
He said the letter included a provision to pressure the Times or the Post to publish the manuscript by specifying that if they refuse, and Penthouse accepts, the man would mail one and only one bomb intended to kill after publication.
Guccione termed that proviso unacceptable and made a counteroffer:
"If he will agree to desist from all terrorist activities as he says he will do in the case of the Times and the Post, including the ad hoc destruction of public property, I will give him one page in the magazine for an indefinite period of time in which he can continue writing his philosophy."
Airlines and mail services remained on guard Friday in California. The U.S. Postal Service said it had instituted new weight restrictions on packages, delayed about 400,000 parcels and would maintain strict security procedures for mail from California until further notice.
Mail weighing 12 ounces or more was returned to senders, and window clerks refused express mail, priority mail, first-class mail, international air mail or military mail weighing more than 12 ounces, the service said.
_ Information from Knight-Ridder Newspapers was used in this report.