HARRISBURG, Pa. — More than 1,000 children — and possibly many more — were molested by hundreds of Roman Catholic priests in six Pennsylvania dioceses, while senior church officials took steps to cover it up, according to a landmark grand jury report released Tuesday.

The grand jury said it believes the "real number" of abused children might be "in the thousands" since some records were lost and victims were afraid to come forward. The report said more than 300 clergy committed the abuse over a period of decades.

Pennsylvania Attorney General Josh Shapiro said the two-year probe found a systematic cover-up by senior church officials in Pennsylvania and at the Vatican.

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"The cover-up was sophisticated. And all the while, shockingly, church leadership kept records of the abuse and the cover-up. These documents, from the dioceses' own 'Secret Archives,' formed the backbone of this investigation," he said at a news conference in Harrisburg.

Significantly, the report faulted Cardinal Donald Wuerl, the former longtime bishop of Pittsburgh who now leads the Washington archdiocese, for what it said was his part in the concealment of clergy sexual abuse. Wuerl defended himself, releasing a statement Tuesday that said he had "acted with diligence, with concern for the victims and to prevent future acts of abuse."

The grand jury scrutinized abuse allegations in dioceses that minister to more than half the state's 3.2 million Catholics. Its report echoed the findings of many earlier church investigations around the country in its description of widespread sexual abuse by clergy and church officials' concealment of it.

As CBS Pittsburgh reports, the report begins with the following statement: "We, the members of this grand jury, need you to hear this. We know some of you have heard some of it before. There have been other reports about child sex abuse within the Catholic Church. But never on this scale. For many of us, those earlier stories happened someplace else, someplace away. Now we know the truth: it happened everywhere."

The report cites 99 priests in Pittsburgh's diocese alone, and of those 99 a group of four groomed and violently sexually assaulted young boys, Shapiro said.

"One boy was forced to stand on a bed in a rectory, strip naked and pose as Christ on the cross for the priests. They took photos of their victim, adding them to a collection of child pornography which they produced and shared on church grounds," Shapiro said.

Shapiro said the priests would mark their victims by giving them gifts.

"To make it easier to target their victims, the priests gave their favored boys' gifts — gold crosses to wear as necklaces. The crosses were markings of which boys had been groomed for abuse," Shapiro said.

Because of an ongoing legal battle, more than a dozen names and identifying information have been redacted. But the report shows a consistent pattern of bishops having prior knowledge of the actions of predatory priests, reassigning them and not alerting law enforcement.

Shapiro said his office is not satisfied with the release of the redacted report. He said each one of the redactions represents a story of abuse that deserves to be told. He went on to say that he will fight to reveal the names currently redacted in the report.

The document comes at a time of renewed scrutiny and fresh scandal at the highest levels of the U.S. Catholic Church. Pope Francis stripped 88-year-old Cardinal Theodore McCarrick of his title and ordered him to a lifetime of prayer and penance amid allegations that McCarrick had for years sexually abused boys and had sexual misconduct with adult seminarians.

Wuerl has come under harsh criticism over his response to the McCarrick scandal, with some commentators questioning his claims of surprise and ignorance over allegations that McCarrick molested and harassed young seminarians.

Wuerl replaced McCarrick as Washington's archbishop after McCarrick retired in 2006.

The Pennsylvania grand jury, convened by the state attorney general's office in 2016, heard from dozens of witnesses and reviewed more than a half-million pages of internal documents from the Allentown, Erie, Greensburg, Harrisburg, Pittsburgh and Scranton dioceses.

Some current and former clergy named in the report went to court to prevent its release, arguing it violated their constitutional rights to reputation and due process of law. The state Supreme Court said the public had a right to see it, but ruled the names of priests and others who objected to the findings would be blacked out pending a September hearing on their claims.

The identities of those clergy members remain under court seal.

A couple of dioceses decided to strip the accused of their anonymity ahead of the report and released the names of clergy members who were accused of sexual misconduct. On Friday, the bishop of Pittsburgh's diocese said a few priests named in the report are still in ministry because the diocese determined allegations against them were unsubstantiated.