Erich Priebke, who turns 100 on Monday, was sentenced to life in prison in 1998 for his role in the 1944 Ardeatine caves massacre, in which 335 people, including 75 Jews, were executed by the Nazis as a reprisal for a deadly partisan attack on German soldiers.
The partisans killed 33 soldiers and Adolf Hitler is reported to have given the order for 10 Italians to be shot for every dead German, or 330 in all.
In the end 335 people were killed and Priebke was accused not only of taking part in the executions, but also for giving the order to kill the five extra people who were rounded up.
After the war, Priebke fled to Argentina where he lived until Italy requested his extradition in 1995. He was put on trial, convicted and handed a life sentence in 1998.
The following year, he pleaded poor health and old age and was given permission to serve the rest of his sentence under house arrest.
The fact that he has never apologized for the massacre and the relatively lax conditions of his house arrest - he can leave the house under escort - have for years been condemned by relatives of his victims.
A party held in the countryside to celebrate Priebke's 90th birthday sparked particular anger.
"I really hope nothing similar will take place this time: it would be an offense not only to his victims but to all Holocaust victims," leftist deputy Sergio Boccadutri said.
There have been recurring complaints over his freedom of movement; photographs published by the Italian weekly Oggi in April 2011 showed Priebke dining at a restaurant with friends, riding a scooter and shopping in a local supermarket.
Lawyer Sebastiano Di Lascio, who represents a families' association, said Priebke should finally apologize.
"I just hope that at least for his 100th birthday he realises what he has done and finds the courage to ask forgiveness," he said.
A close friend Mario Merlino, nicknamed 'professor black' for his neo-fascist past, told the Corriere della Sera daily that the former SS officer "has got a lot closer to Christianity, perhaps because he feels his end is near. He reads sacred texts, he meditates. He is deaf and has almost entirely lost his memory."
"We will make him remember," said Angelo Sermoneta, 65, who runs Rome's historical Jewish community association, Ragazzi del 48.
"We're likely to do something to mark the day. Our younger generations are always ready to rally, but Priebke unfortunately has never repented and he will never repent," he said.
"The Italian authorities treat him too well. He is escorted on walks, to the park, to restaurants. He who has denied so many people an old age is living such a serene one himself," he added.
Priebke's centenary comes on the heels of the Nazi-hunting Simon Wisenthal Centre launching a campaign seeking information on the last perpetrators of the Holocaust still at large, hanging posters on the streets of major German cities with the words "Late but not too late."
"In my 33 years of hunting Nazis I never once had a case of a Nazi who ever said he was sorry," said Efrain Zuroff, the campaign's initiator.
"Don't look at these people and see a frail old man or woman, think of someone who at the height of his physical strength devoted his energy to murdering innocent women and men. These are the last people on Earth deserving any sympathy because they had absolutely no sympathy for their victims."