The Munich daily newspaper Sueddeutsche Zeitung said on Monday that Scheungraber's prosecution in Germany "is possibly... the last major trial for crimes committed under the Nazis".
A handful of protesters gathered outside the courtroom holding a placard reading: "Mass murderer here! Give the murdered a name."
The defendant, dressed in a traditional Bavarian suit, appeared to be in good health and alert as he walked with a cane to his seat in the courtroom.
Scheungraber faces 14 counts of murder and one of attempted murder. He followed the proceedings with headphones due to his poor hearing.
The accused "completely and thoroughly denies the accusations in the charge sheet," said a statement read in court by Christian Stuenkel, one of his two lawyers.
At the start of proceedings, the prosecution's opening arguments described an account of the day of June 26, 1944.
The German troops are alleged to have first shot dead a 74-year-old woman and three men in the street before placing 11 others into the ground floor of a farmhouse which they then blew up.
Gino Massetti, a 15-year-old boy, survived seriously injured, and testified during the Italian trial.
Massetti, now 79, has told the German press he has no desire to exact vengeance.
"I just want to forget those horrible moments," he said.
Scheungraber has lived for decades as a free man in Ottobrunn outside Munich, where he has served on the town council and run a furniture shop.
He regularly attended marches with fellow wartime veterans and recently received an award for municipal service.
A lawyer for Italian relatives of the victims, who are co-plaintiffs in the trial, said her clients wanted Scheungraber to finally take responsibility for the killings.
"They have waited 64 years for someone to atone for their loved ones' deaths," she told the court.
The defendant said in his statement that he had not given an order for the killings and was not at the scene of the crime.
His defence team said prosecutors had no witness who could testify to Scheungraber's involvement.
Scheungraber was not jailed pending his trial as prosecutors said there was little risk he would flee the country.
Due to his age, he will only be asked to sit in court for a few hours at a time.
The military tribunal at La Spezia has tried several former Nazis for crimes committed in Italy during World War II but none of the defendants have been brought to justice.
Scheungraber's trial will resume September 29.