German authorities are pressing for a 100-year-old former Nazi concentration camp guard to face trial almost 80 years after the end of the second world war.

The higher regional court in Frankfurt said on Tuesday it had overturned a decision by a lower court under which the suspect had been deemed unfit to stand trial.

The suspect, named as Gregor Formanek by German media, was charged last year with aiding and abetting murder in 3,322 cases while working at the Sachsenhausen concentration camp near Berlin between July 1943 and February 1945.

However, an expert determined in February that Formanek was not fit to stand trial due to his mental and physical condition and the court in Hanau decided not to open the proceedings against him.

The Frankfurt court on Tuesday found the expert’s decision had not been based on “sufficient facts”.

“The expert himself stated that it was not possible to interview the defendant and that the opportunity for extensive psychiatric testing was not available,” it said.

Germany has been scrambling to bring the last surviving former Nazi war criminals to justice since a 2011 landmark ruling paved the way for several trials.

One former Nazi camp guard, John Demjanjuk, was convicted in 2011 on the basis that he served as part of Hitler’s killing machine, even though there was no proof he had directly killed anyone.

Since then, several former concentration camp workers have been found guilty of being accessories to murder on the same basis.

However, with time running out, many cases have been abandoned in recent years after the accused died or were physically unable to stand trial.

More than 200,000 people, including Jews, Roma, regime opponents and gay people, were detained at the Sachsenhausen camp between 1936 and 1945.

Tens of thousands died there from forced labour, murder, medical experiments, hunger or disease before the camp was liberated by Soviet troops.