"Hundreds of pupils were beaten," Thomas Pfister told a news conference on Friday, March 5. "There were very extreme cases of mistreatment which normally would have been punished with long prison sentences."
Instead, Pfister said, "a cloak of silence was thrown over the charges."
The statute of limitations has lapsed on most of the cases, meaning individuals can no longer be prosecuted, but the Catholic Church appointed Pfister to investigate what happened at the Benedictine school in Ettal in response to an ever-widening abuse scandal involving several Catholic schools across Germany.
Pfister said 100 boys may have been victims in Ettal alone.
One priest's admission
Ettal Monastery treasurer Johannes Bauer also admitted to brutally beating pupils while he was a teacher there between 1985 and 1987.
"To my shame, I have to say openly that I also brutally abused children physically and humiliated them," he said. "I am very sorry and ask forgiveness from the bottom of my heart."
The Vatican has been consulted by the monastery about how best it can take a "new spiritual direction."
Four priests are suspected to have been involved in the abuse, one of whom is dead. In connection with the accusations, three monks at the Wechselburg monastery in Saxony have now been suspended.
The investigator added, however, that the offences were relatively limited, with 10 priests accused in total.
"To imagine the abbey as a community of sadistic raping monks would not be accurate," said Pfister.
Police in Munich are also investigating one teacher who is a currently a priest at the school. He allegedly posted pictures on websites showing his bare-chested pupils during hikes in the Alps.
More allegations across Germany
Ettal is one of three church schools in Bavaria which have been rocked by allegations of clerical abuse.
The Regensburger Domspatzen choir school, which was once headed by Georg Ratzinger, the brother of Pope Benedict XVI, is at the centre of allegations from three former pupils that sexual abuse took place there in the early 1960s. Two former senior teachers at the school were jailed, in 1958 and 1971, for pedophile sex, according to the Regensburg diocese.
Meanwhile, the Capuchin order said that a former director of its Burghausen school sexually molested pupils between 1984 and 1985.
Nationwide, more than 150 other people have contacted church-appointed lawyers, describing incidents of abuse at various church schools.
The Catholic Church has come under heavy attack in Germany after details of abuse at the elite Jesuit Canisius College in Berlin were made public earlier this year.
A spokesman for the Vatican on Friday said it was "taking very seriously all aspects of the pedophile scandal in Germany."
Editor: Andreas Illmer