Lawyers for former JonBenet Ramsey slaying suspect John Mark Karr renewed efforts to get child pornography charges against him dismissed, despite a judge's ruling last week that the case could proceed.

Defense lawyers, who argue that five misdemeanor charges against John Mark Karr should be dropped because prosecutors lost the computer that allegedly held the pornographic images, also seek to block newly discovered computer evidence from being admitted at trial.

Click Here to Crack the Case in FOXNews.com's Crime Content Center

Click here to visit FOXNews.com's Law Center

Prosecutors "don't know how the images got there," Karr's lawyer, Robert Amparan, said of the new evidence. "They don't know whether Mr. Karr knew they were there. They don't know when, if ever, they were viewed."

Karr's trial was scheduled to start Monday, but was postponed for further hearings Tuesday on the defense motions.

Sonoma County authorities said they've found more than 1,000 other child pornography images on diskettes, CDs and a removable disk drive that were seized from Karr's home in 2001 with the computer. They said during a hearing Monday that the investigation continued, even as his trial approached.

Deputy County Counsel Anne Keck told Sonoma County Superior Court Judge Cerena Wong that the FBI was reviewing other pornographic images and comparing them against a national database to determine whether underage children appear in the photos.

Prosecutors have said the evidence should remain under seal because of the ongoing investigation of Karr, who recently was returned from Colorado to face the five-year-old porn charges.

But FBI spokesman Joe Schadler later said the bureau's role in the Karr investigation had ended, and was limited to providing expert testimony and forensic analysis of the five pictures that led to the initial charges.

"We're not doing any further forensic work," he said.

Keck did not return phone messages from The Associated Press seeking comment. Defense lawyers did not comment on the FBI's involvement in the investigation.

Wong refused to unseal the documents sought by The Press Democrat newspaper of Santa Rosa. She sealed affidavits and other police documents after prosecutors said it could harm the investigation and prejudice potential jurors.

Karr, 41, appeared in court briefly, looking tired and worn after spending more than a month in jail. Speaking in a soft voice, he waived his right to appear at the hearing and was led away by sheriff's deputies.

Karr has rejected a plea deal that would have put him on probation. Prosecutors, who have conceded he probably won't serve more time if convicted because he already spent several months in jail awaiting trial five years ago, said they want him to register as a sex offender.

Karr, who fled after being released in 2001, remains jailed on $200,000 bail.

The former teacher was arrested in Thailand after suggesting he killed JonBenet, a 6-year-old beauty queen, in her Boulder, Colo., home in 1996. The Ramsey case quickly collapsed after DNA failed to connect him to the crime.