The trial of suspected Nazi mass murderer John Demjanjuk may have been based on fabricated evidence, the FBI has claimed.

Lawyers for the 90-year-old Ukrainian accused of being a guard at the SS death camp Sobibor during World War Two today asked for the trial to be suspended in the light of the report.

At issue is Exhibit A in the case, Demjanjuk's alleged SS identity card.

[W.Z. The original URL listed above shows an excellent image of the Demjanjuk photograph on the ID card -- with misaligned circular stamps on the lower-left and upper-right of the photograph. Expert witness for the prosecution, Larry Stewart, (both in Munich in 2010 and the United States in 2001) fraudulently claimed that the lower-left stamp could be brought into alignment by shifting and rotating the card slightly. However, he neglected to point out that such manipulation causes the misalignment in the upper-right stamp to increase drastically. This has been conclusively demonstrated by Lubomyr Prytulak on his website at http://www.xoxol.org/traw/stewart.html  .]

According to an FBI report from 25 years ago that has just surfaced, the agency deemed that it was 'quite likely fabricated' by KGB agents in the former Soviet Union.

Over three decades of U.S. hearings, an extradition, a death sentence followed by acquittal in Israel, deportation to Germany and now a trial in Munich due to end next month, the arguments have relied heavily on the photo ID.

It comes from the SS training camp of Trawniki, Poland, stating one Ivan Demjanjuk was sent to Sobibor, 40 miles away, and participated in the murders of more than 28,000 Dutch Jews deported there between March and September 1943.

Ivan, the Russian for John, changed his name in 1956 in America.

Claims that the card and other evidence against Demjanjuk are Soviet forgeries have repeatedly been made by his defence lawyers.

However, the FBI report provides the first-known confirmation that U.S. investigators had similar doubts.

'Justice is ill-served in the prosecution of an American citizen on evidence which is not only normally inadmissible in a court of law, but based on evidence and allegations quite likely fabricated by the KGB,' the FBI's Cleveland field office said in a 1985 report -- four years after the Soviets had shown U.S. investigators the card.

Demjanjuk, a Soviet citizen who fled to the U.S. in 1952, should - under international agreements - have been sent back to Ukraine.

He lied on his paperwork, claiming he had been out of Ukraine since before the war started and had spent it farming in Sobibor, Poland.

In 1975, after he and his wife Vera had become U.S. citizens, he wrote to his mother in Ukraine to say he was still alive.

She then cancelled her pension as the mother of a dead soldier.

Demjanjuk had served in the Red Army before being captured by the Nazis in 1942, and Soviet officials went snooping in the files and came up with the disputed ID card.

FBI agents argued that the Soviets had an interest in faking the documents as part of a campaign to smear anti-communist emigres.

The report was found by the U.S. news agency AP at the National Archives in College Park, Maryland.

But the card has since been authenticated by experts in Germany who declare it to be real.

Besides, duty rosters of guards at Trawniki were found in German archives bearing Demjanjuk's name - something, say German prosecutors, that could not possibly have been faked by the Soviets.

Demjanjuk always claimed he was captured by the Nazis, imprisoned and volunteered to fight in a anti-Communist German unit called the Vlasov Army.

Prosecutors say this version of events is false, claiming instead he went to work at Sobibor, one of 3,500 Ukrainians who manned the secret death camps.

Acquitted in Israel in 1993 of being Ivan the Terrible, a particularly brutal guard at the Treblinka extermination camp, he was freed.

But judges in the Israeli trial said 'all the evidence' pointed to Demjanjuk as having served at Sobibor.

Prosecutors in Germany, who got him extradited to Munich in 2009, have asked for him to be sentenced to six years jail when the verdict is handed down on May 12, 2011.