ROME—By now nothing should surprise us about what goes on behind the protective walls of the not-so Holy See. But the latest book by Italian investigative journalist Gianluigi Nuzzi, titled Original Sin delves far beyond the sleazy rumors and alleges blatant criminal activity in Vatican City.

Two of Nuzzi’s last books, Merchants in the Temple published in 2015 and His Holiness published in 2012, landed the best-selling author in a Vatican courtroom for the so-called Vatileaks trials. This time, Nuzzi tells The Daily Beast he had his new book hand-delivered to the Vatican’s chief prosecutor. “There is proof of crimes committed by clerics against children,” he says. “Let’s see what they do with it.”

The book is filled with salacious scoops, backed up by copies of documents printed in an exhaustive index. He shines a light on the disappearance of 15-year-old Emanuela Orlandi, the daughter of a Vatican employee who went missing 30 years ago after a music lesson and whose body has never been found. Conspiracy theorists waffle between theories that she was kept as a sex slave for priests for years or that she was murdered by a local Roman gang of criminals as a threat to her father, who may have witnessed a crime.

Nuzzi provides interview transcripts, sealed court documents and secret video from when police opened a mobster’s tomb in Rome to search for her body to support the theory that she was murdered by an “international group” that Pope Francis has been made aware of. He asks if justice has or will ever be served in the case.

He also seeks to correct the theory that Pope John Paul I, who reigned just 33 days prior to the election of Pope John Paul II, was murdered. Instead he says he succumbed to the weight of the corruption and criminality he was charged to deal with.

Nuzzi also sullies the legend of Mother Teresa of Calcutta, made a saint by Francis in 2016. He has uncovered accounting slips from secret bank accounts, in dollars and Italian lire, that the austere nun kept in her charity’s name in the troubled Vatican bank during the time when American archbishop Paul Marcinkus led the institution.

Nuzzi said her accounts were so flush that if she had withdrawn the money or transferred to a more legitimate institution, the bank “risked default.” The nun, whose net worth is thought to be in the billions in the name of her charity, was such a valued client that she was ushered in through a secret door so no one suspected she was the bank’s wealthiest patron at a time when most women were prohibited from having accounts in their own names.

Nuzzi uses the example to prove the existence of a network of administrators who still control the purse strings and reign over the Vatican’s considerable wealth, who he says are so powerful they have blocked some of Francis’s reforms and who were instrumental in Pope Benedict XVI’s decision to retire, essentially pushing him out of office.

But the most troubling revelation in the book is one that Nuzzi himself admits he only scratched the surface of. He provides horrific proof of widespread sexual abuse inside San Pio X, the pre-seminary boarding school where middle school and high school age boys who express interest in joining the priesthood are still sent today.

The boys of the institute, housed in the same majestic building where former Vatican secretary of State has a controversial penthouse apartment which was recently renovated with funds from the Vatican’s children’s hospital, officially serve as altar boys at Vatican masses and choir boys for St. Peter’s basilica. But the author also alleges they are actually nothing short of play things for the Vatican priests who like sex with young boys.

Nuzzi interviewed a former seminarian thought to be a victim and published disturbing phone transcripts in which priests discuss playing with the boys, how ejaculate was referred to as “milk” and that oral sex was described as “a game” that should only be played once every two days.

He also amplifies the accusations of a Polish man named Kamil Tadeusz Jarzembowski, who was a student at the pre-seminary when he was 13 years old and who has sent a number of complaints about what he saw to the Vatican’s Congregation for the Doctrine of the Faith, which acts as gatekeeper for such accusations to determine their legitimacy. Despite saying he witnessed at least 140 sexual acts by an older priest who was “favored by various monsignors in the Church” on his underage roommate, he was eventually expelled from the seminary.

Specifically, he says the older priest who was “able to exert a form of power and intimidation” over the young boys, engaged in oral sex in his presence with the young boy and sometimes took him to his private chambers for other sexual activities. Jarzembowski also said that the priests who run the boys school “say mass in the morning and go to Mucca Assassina at night” referring to a well known gay disco in Rome. The Vatican did not respond to a request for comment about the allegations.

Nuzzi told The Daily Beast that of all the revelations in his book, the “choir boy accusations” are the most important. “Pay attention to that story,” he said. “It will surely grow. Or at least it should.”