CLEVELAND (AP) — A recently deceased Ohio autoworker convicted of Nazi war crimes should have his U.S. citizenship restored because the American government withheld potentially helpful material, his attorneys said.

The defense team for John Demjanjuk, who died March 17 in Germany at age 91, asked the 6th U.S. Circuit Court of Appeals in Cincinnati to restore his citizenship or order a hearing on the case.

The filing late Thursday night said U.S. District Judge Dan Polster in Cleveland erred last year in refusing to reopen the citizenship case at Demjanjuk´s request.

Demjanjuk, who lived for decades in Seven Hills in suburban Cleveland, was convicted by a Munich court in May on 28,060 counts of being an accessory to murder at the Sobibor death camp in occupied Poland. The Ukrainian-born man maintained that he had been mistaken for someone else; he died while his conviction was under appeal.

A political leader in the Ukraine told The Associated Press that Demjanjuk´s body was returned to the U.S. for burial. Rostislav Novozhenets, deputy head of the nationalist Ukrainian Republican Party, said in a telephone interview that Demjanjuk was buried March 31 at an undisclosed location. Family members living nearby will care for the gravesite, Novozhenets said.

Dennis Terez, a public defender representing Demjanjuk, said Friday he couldn´t comment on where Demjanjuk was buried.

Prosecutors have until next month to file a response to the citizenship issue, Terez said. The defense will then get a chance to reply.

The government rejected the defense´s arguments.

"In a reasoned and meticulously supported decision, Judge Polster rejected these same contentions by Mr. Demjanjuk´s lawyers," spokesman Mike Tobin, of the U.S. attorney´s office in Cleveland, said in an email.

"While the department continues to litigate this matter in court, the latest filing contains no new information on this decades-long matter."

David Leopold, an immigration attorney in Cleveland, said he had never seen citizenship restored posthumously in a war crimes case. He said there is sufficient evidence against Demjanjuk for the appeals court to reject the latest bid.

According to the defense filing, Polster violated basic fairness by ruling against Demjanjuk´s citizenship appeal without holding a hearing on a newly discovered document.

The document, a 1985 secret FBI report uncovered by The Associated Press, indicates the FBI believed a Nazi ID card purportedly showing that Demjanjuk served as a death camp guard was a Soviet-made fake.

"Anything that would cast doubt onto the legitimacy of the government´s case against a naturalized citizen should be highly relevant and material," the defense filing said.

The government responded to the document with an Oct. 12 affidavit from retired FBI agent Thomas Martin, who said the 1985 report written by him was based on speculation, not any investigation.

He said he had based his speculation, in part, on his understanding that the Soviet secret police "had a longstanding program designed to target dissidents living overseas, for the purpose of intimidation, threat or actual assassination."

While concerned the Nazi ID card could be a Soviet fake, Martin said in the affidavit, "I reached no conclusions about its authenticity."

But such affidavits should not be allowed to go unchallenged, the defense said. The judge "did not even see all of the withheld materials," the filing said.

The filing said it would be unusual for an FBI agent to submit a report to Washington headquarters based only on conjecture, as portrayed by federal prosecutors.

The filing also said the citizenship case could bear on unresolved legal issues in Germany, including whether German courts had jurisdiction, and noted that Demjanjuk´s death came before his appeal was heard, raising a question of finality.

Demjanjuk was tried, convicted and sentenced to death in Israel as the notoriously brutal guard "Ivan the Terrible" at the Treblinka extermination camp. The Israeli Supreme Court unanimously overturned the conviction after Israel received evidence that another Ukrainian, not Demjanjuk, was that Nazi guard.

When they overturned his conviction in Israel, the supreme court judges there said they still believed Demjanjuk had served the Nazis, probably at the Trawniki SS training camp and Sobibor. But they declined to order a new trial, saying there was a risk of violating the law prohibiting trying someone twice on the same evidence. ___Associated Press stringer Svetlana Fedas in Lviv, Ukraine, contributed to this report. (© 2012 The Associated Press 04/13/12)