A 90-year-old former Nazi soldier has been handed a life sentence for his role in a wartime massacre on the Greek island of Cephalonia, the setting for the bestselling novel Captain Corelli's Mandolin.

Alfred Stork, a German ex-corporal, was sentenced in absentia by a military court in Rome which found him guilty of taking part in the execution of at least 117 Italian officers who had surrendered to the Nazis.

The massacre on 24 September 1943 was just one bit of a far bigger and bloodier German massacre of Italian troops, whom they regarded as traitors for having switched sides after Italy signed an armistice with the Allies.

Around 5,000 Italian soldiers from the Acqui division on Cephalonia were rounded up and killed by the Nazis after surrendering following a bloodthirsty, week-long battle.

The atrocity – one of the worst examples of Nazi brutality – was described in Louis de Bernières's novel, Captain Corelli's Mandolin, which was subsequently turned into a film starring Penelope Cruz and Nicolas Cage.

The hero, Captain Antonio Corelli, is a gregarious officer in the Acqui division. He narrowly escapes being killed in the massacre.

Stork's defence had argued that he should be cleared of the charges due to a lack of proof and the fact that, in any case, as a corporal he would have had to have followed orders.

But the military prosecutor said witness testimony had proved beyond reasonable doubt that Stork had taken part in the incident.

In 2005 the ageing German allegedly admitted he had formed part of an execution squad that killed some of the officers, but the evidence was not admissible in the Italian court.

The prosecutor Marco de Paulis told the court Stork "did not have the courage" to stick to his admission, instead "staying comfortably" in his house in Germany.