TORONTO -- The federal government has hit another roadblock in its decades-long effort to strip Canadian citizenship from a now 92-year-old man who was once a member of a brutal Nazi death squad.

In its decision, the Federal Court of Appeal set aside a ruling against Helmut Oberlander and ordered the government to take another look at the case.

Oberlander, an ethnic German born in Ukraine, has argued he had no choice when German forces conscripted him at age 17 in 1941 to serve as an interpreter in Einsatzkommando 10a. The unit was part of a force responsible for killing more than two million people. Most were civilians, and most were Jewish.

"The appellant was entitled to a determination of the extent to which he made a significant and knowing contribution to the crime or criminal purpose of the Ek 10a," the Federal Court of Appeal said in its recent decision.

"Only then could a reasonable determination be made as to whether whatever harm he faced was more serious than the harm inflicted on others through his complicity."

In making its decision, the court noted the Supreme Court in 2013 ruled that individuals cannot be held liable for a group's crimes only because they associated with the group or passively acquiesced to its criminal purpose.

Oberlander, who immigrated to Canada with his wife in 1954 and raised two daughters, became a citizen in 1960 and ran a construction business in Kitchener, Ont. The government first began trying to strip him of his citizenship in 1995, prompting a hotly contested and protracted court battle.

In 2000, Federal Court concluded Oberlander had obtained his citizenship fraudulently -- either by lying on his application or by hiding his Second World War activities. Ottawa moved again to revoke his citizenship, leading to one appeal that ended in 2004 with the case being sent back to the government for a new decision.

In 2007, the government again revoked his citizenship, prompting a new round of appeals.

Two years later, the Federal Court of Appeal ruled the government had been reasonable in finding Oberlander's membership in Einsatzkommando 10a made him complicit in its war crimes he knew were happening.

However, the court also said Ottawa should have considered the issue of whether he had acted under duress and sent the matter back for further consideration.

Ottawa reviewed the issue and rejected the idea that Oberlander had acted under duress.

He had failed to show, the government argued, that he feared execution in order to justify his complicity in the actions of the killing squad. In 2012, it again revoked his citizenship on the grounds he had been a member of Ek 10a and, as a result, could be "suspected of being complicit in the activities of a limited brutal-purpose organization."

Oberlander appealed again to Federal Court, which rejected his arguments, and then to the Federal Court of Appeal, which has now sent the matter yet again back to the government.

Oberlander's lawyer Ron Poulton said Tuesday said his client has never been found to have committed or aided and abetted a war crime.

"His complicity was based solely on membership and on a now debunked principle of guilt by mere association," Poulton said.

"Mr. Oberlander was forced against his will to associate with Ek 10a. His contribution to their criminal purposes was insignificant."