Helmut Oberlander, 92, was in death squad estimated to have killed 23,000 civilians and has lived in Canada since 1954

A 92-year-old man who served with a Nazi death squad has won a fresh reprieve in his 20-year legal battle against deportation from Canada.

Helmut Oberlander was part of the Nazi Einsatzkommando 10a (Ek10a), which is estimated to have killed 23,000 civilians – mostly Jews – during the second world war.

The Ukrainian-born German, who joined the squad at the age of 17, has never been charged with any war crime but is included in the Simon Wiesenthal Centre’s annual list of the most wanted Nazi war criminals.

Oberlander has been fighting to retain his Canadian citizenship since 1995, when the legal case against him began. He argues he only cooperated with the German unit under duress and merely served as a translator who never participated in any killings.

Oberlander arrived in Canada in 1954 and became a citizen six years later without disclosing his wartime experiences.

In a statement on Monday, Shimon Koffler Fogel, the head of Canada’s Centre for Israel and Jewish Affairs, said Oberlander was “contriving to abuse the judicial system to avoid responsibility”.

He added that Oberlander “was a member of one of the most savage Nazi killing units ... That he clearly lied about his wartime past to fraudulently gain entry into this country is not in question – nor the legal consequences of falsification of immigration documents.

“He is here illegally and he ought to have his Canadian citizenship revoked.”

Oberlander’s lawyer, Ronald Poulton, told the National Post his client’s role in the death squad was “limited and forced”. His daughter, Irene Rooney, told reporters last year that recent months for her father had been “especially tough, since he lost his wife of 62 years to cancer, but he will carry on because he wants to see justice done and wants his good name restored”.

Oberlander was stripped of his citizenship by the federal cabinet in 2001 after a court found he had falsely represented or concealed his past when making an application for residency.

The court of appeal overturned that ruling in 2004 and sent the case back to cabinet for reconsideration. But the cabinet was unmoved and once again revoked Oberlander’s citizenship in 2007.

The court of appeal again overturned the decision in 2009 and ruled the cabinet must consider whether Oberlander was forced to join the death squad under duress. In 2012, the cabinet found the defence of duress had not been established and revoked his citizenship for the third time.

The decision was upheld in 2015 by the federal court judge James Russell, who said Oberlander never sought to be relieved of his duties nor expressed remorse for his membership of the death squad.

But in the latest ruling, the appeal court has once again sent the matter back to cabinet on the grounds that Russell failed to take into account a 2013 supreme court ruling that found the principle of “guilt by association” was unjust and wrong.

“To be complicit, ‘there must be serious reasons for considering’ that the person concerned ‘voluntarily made a significant and knowing contribution to the organization’s crime or criminal purpose’”, the new ruling states.

Poulton told the National Post: “It is hard to imagine how he could be held accountable now, given his limited and forced role with the unit.”

It is not clear whether Oberlander will be extradited to stand trial at the international criminal court in the Hague. Bernie Farber, the former chief executive of the Canadian Jewish Congress, said last year: “My guess is he’ll live the rest of his life in Canada. He never took a scintilla of responsibility for anything, and I think for the most part that has turned so many against him. He refused to recognise that he was a participant in an evil or illegal organisation.”

Karen Redman, a former Canadian MP, said in 2000 she had received numerous petitions from residents of Kitchener-Waterloo in Ontario, where Oberlander lives, stating that the finding of fault with the immigration process should not form the basis for citizenship revocation and deportation.

“Mr Oberlander has been a good citizen of Canada and a contributing member of the community for over 40 years, the petitioners call upon the federal government not to revoke the citizenship or deport Helmut Oberlander of Waterloo,” she added.