DENVER— Lawyers for Oklahoma City bombing conspirator Terry Nichols said Wednesday his conviction and life sentence should be overturned because the jury did not rule on whether he knew people would die.

Nichols, 45, was found guilty of conspiracy and eight counts of involuntary manslaughter in the 1995 federal building bombing, which killed 168 people.

His defense lawyer, John Richilano, asked U.S. District Judge Richard Match on Wednesday to vacate the conviction and sentence because jurors were not asked to determine whether Nichols knew what would happen in the bombing.

He said jurors needed to make that determination to convict.

Prosecutor Sean Connelly said jurors found that Nichols took part in a conspiracy that resulted in death, and that the deaths were a foreseeable result of the conspiracy. He said those findings justify a life sentence for Nichols.

Richilano also argued that Nichols deserved a new trial because Matsch refused to allow FBI scientist Frederick Whitehurst to testify about problems handling evidence at the agency's laboratory. Matsch said two other witnesses had already made the same argument.

The judge did not rule on the arguments Wednesday.

One of Nichols' defense attorneys, Barry Schwartz, said this could be Nichols' last round of challenges unless substantial new evidence is found.

Convicted bomber Timothy McVeigh is scheduled for execution May 16.