On 20 February 1998, Judge Paul Matia of the U.S. District Court for the Northern District of Ohio vacated Demjanjuk's denaturalization "without prejudice," meaning that OSI could seek to strip Demjanjuk of citizenship a second time. OSI continued to investigate Demjanjuk, relying solely on documentary evidence rather than eye-witnesses. These documents were found in former Soviet archives in Moscow and in Lithuania, which placed Demjanjuk at Sobibor on 26 March 1943, at Flossenbürg on 1 October 1943, and at Majdanek from November 1942 through early March 1943; administrative documents from Flossenbürg referencing Demjanjuk's name and Trawniki card number were also uncovered. On 19 May 1999, the Justice Department filed a complaint against Demjanjuk to seek his denaturalization. The complaint alleged that Demjanjuk served as a guard at the Sobibór and Majdanek camps in Poland under German occupation and as a member of an SS death's head battalion at Flossenbürg. The complaint relied on evidence compiled by historians Charles W. Sydnor, Jr. and Todd Huebner, who compared Demjanjuk's Trawniki card to 40 other known cards and found that issues on the card that had fueled suspicions of fraud were in fact typical of Trawniki's poor record keeping.