DENVER (CNN) -- A U.S. judge may be inclined Thursday to impose a life sentence on Terry Nichols, the convicted co-conspirator of the Oklahoma City bombing, unless Nichols decides to talk.

U.S. District Judge Richard Matsch has said he may impose a lesser sentence only if Nichols will disclose information about the April 19, 1995, bombing that killed 168 people and injured more than 500 others.

Defense attorneys say Nichols likely will disclose nothing Thursday because he still faces state murder charges.

Matsch has not specified the questions he wants answered, but Nichols' attorneys have implied that other conspirators are still at large.

Nichols has said nothing publicly since his arrest shortly after the bombing. He expressed remorse in a letter written to Matsch after the trial ended last year.

Nichols, his attorneys say, is in a tight spot because any information he reveals could be used against him by Oklahoma prosecutors, who plan to try Nichols and the bombing's convicted mastermind, Timothy McVeigh, on murder charges. The Oklahoma prosecutors have vowed to seek the death penalty.

Nichols was convicted in December of conspiracy and eight counts of involuntary manslaughter. The jury acquitted him of murder and weapons-related charges. The panel failed to agree on a sentence, which is why the task falls to Matsch.

Alfred P. Murrah Federal Building after April 19, 1995, bombing

Prosecutors have asked Matsch to abide by the guidelines, and sentence Nichols to life in prison. Under federal law, Matsch cannot impose the death penalty.

Nichols' attorneys have recommended a maximum term of seven years, insisting their client was building "a life, not a bomb."

On Tuesday, a psychiatrist hired by the defense submitted a letter to Matsch that said Nichols is not violent.

Dr. James Gordon of Georgetown University said he reached his conclusion by reading letters written by and about Nichols.

"Though it seems plausible that Terry Nichols participated in the conspiracy that Timothy McVeigh designed ... it is extremely difficult to believe that he intentionally took anyone's life or indeed took part in any activity which might conceivably take someone's life," Gordon wrote.

In response, Dr. Reid Meloy, a forensic psychiatrist and professor at the University of California-San Diego, submitted an evaluation of Nichols on behalf of the government.

Meloy said he agreed with Gordon's assessment that Nichols is a "loner ... reclusive, even suspicious" personality.

That is "quite consistent with what we would expect in a bomber," Meloy said.

"Mr. Nichols, 13 years older (than McVeigh), provided the ... stable anchor for the conspiracy to unfold," Meloy concluded.

Nichols' son Joshua will attend the sentencing

Nichols' father, his former wife Lana Padilla and son Joshua plan to attend Thursday's sentencing. Some of the jury members and victims of the Oklahoma City bombing plan to attend too.

Nichols' current wife, Marife, will not be there. She has returned to her home in the Philippines along with the couple's two young children.

Last year, a separate jury convicted McVeigh, Nichols' former U.S. Army buddy, of the bombing and sentenced him to death.

Another Army colleague, Michael Fortier, who gave crucial testimony in both trials, was given a 12-year prison sentence last week for failing to alert authorities before the bombing and other charges.

Correspondent Tony Clark, The Associated Press and Reuters contributed to this report.