Several hundred Roman Catholic priests in Pennsylvania were accused of sexually abusing more than a thousand children, a grand jury report on Tuesday said, in an alleged “cover-up” described as “sophisticated” by the state’s attorney general.

Over the course of a two year investigation, launched by Pennsylvania Attorney General Josh Shapiro’s office, a grand jury heard several witness statements and pored over documents from six dioceses in the state.

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Those dioceses included Allentown, Erie, Greensburg, Harrisburg, Pittsburgh and Scranton. Upwards of 300 "predator priests" stand accused of the decades-long abuse, the report said.

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

It’s possible that the “real number” of abused children could be “in the thousands” due to missing records or other victims who feared speaking about the allegations, according to the grand jury’s report.

In order to prevent the Catholic Church from suffering bad publicity or financial liability, the panel claimed that a series of bishops and other diocesan leaders attempted to hide the alleged abuse.

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The report faulted Cardinal Donald Wuerl, the former longtime bishop of Pittsburgh who currently 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 Associated Press contributed to this report.