An aging Chicago (search) carpenter should be stripped of his U.S. citizenship because he was a member of a police unit that helped the Nazis (search) round up Ukrainian Jews for forced labor and death camps during World War II (search), federal attorneys argue.

"He acquiesced in conduct contrary to civilization and decency," government attorney Gregory Gordon told U.S. District Judge Samuel Der-Yeghiayan (search) as a civil trial against Osyp Firishchak (search) began Monday.

Firishchak, 86, came to the United States after World War II, settled in Chicago and obtained American citizenship. But the Justice Department's Nazi-hunting Office of Special Investigations (search) says he lied on his visa application and broke other rules.

The government says he joined the Ukrainian Auxiliary Police and helped in widespread roundups of Jews who were sent to forced labor camps and death camps after the Germans occupied Ukraine (search) in 1941.

If Der-Yeghiayan rules against him, Firishchak would be stripped of his citizenship. The government then likely would seek to deport him.

Defense attorney James Maher III told the judge that Firishchak was never a member of the Ukrainian Auxiliary Police and that there is no proof he did any of the things the government claims. Maher also said there is nothing to suggest Firishchak was dishonest on his visa application.

The government's first witness, Holocaust researcher Dieter Pohl (search), described what happened to the Jewish population in the city of Lviv at the hands of the Ukrainian Auxiliary Police.

"There was constant violence against the Jews," Pohl said.

Firishchak's name of surfaced after the fall of the Soviet Union when the newly independent Ukraine opened its archives to Holocaust researchers.

Government attorneys acknowledged they have only a smattering of direct evidence that specific acts allegedly were committed by Firishchak. But they say they can prove he was part of the auxiliary police throughout the war and that the unit was instrumental in carrying out the Holocaust (search) in Ukraine.