The report is thought to be the most comprehensive to date into abuse in the USA church, but while prosecutors have filed charges against two priests, the vast majority of crimes happened too long ago to prosecute under current laws.
"The cover-up was sophisticated".
The report is made up of years' worth of testimony but also numerous church's own records, files known to priests as the "secret archives", where accusations of abuse were kept and hidden away until now.
"These documents, from the dioceses" own 'Secret Archives, ' formed the backbone of this investigation, ' he said at a news conference in Harrisburg.
A grand jury report examining six out of the eight Catholic dioceses in Pennsylvania details more than 1,000 instances of sexual abuse allegedly committed by hundreds of Catholic priests in the state.
The groundbreaking investigation into sexual abuse in the Catholic Church in Pennsylvania has raised questions about Cardinal Donald Wuerl, who spent 18 years as the bishop of Pittsburgh and now serves as the archbishop of Washington.
In a statement Tuesday, the Cardinal said he "acted with diligence, with concern for the victims and to prevent future acts of abuse".
Not all who are accused of sexual abuse or of covering it up in the report are priests.
Sources close to the cardinal also point out that the grand jury report does not distinguish between proven incidents of abuse and other allegations, saying that the report presumes that any priest accused of abuse should have been permanently removed from ministry, whether the allegation is proven or not.
Sexual abuse scandals have rocked the Roman Catholic Church for decades, not just in the USA but throughout the world.
The grand jury report says the diocese in Erie, Penn. and the diocese in Hawaii knew that Hannon had "admittedly abused at least 20 youths" who were between the ages of 12 and 19.
He said the grand jury identified about a thousand victims, but believed there may be many more.
Victim advocates call the report the largest and most exhaustive such review by any USA state.
Small parts of the voluminous report were made public in advance of the release via court documents.
This included downplaying accusations of rape and molestation with euphemisms like "horseplay" and "wrestling", transferring accused priests around the country or placing them on "health leave" while keeping them on the church payroll - at times to the tune of tens of thousands of dollars.
The grand jury recommended that criminal and civil statutes of limitations on sexual abuse in Pennsylvania be reformed to prosecute the detailed allegations of sexual abuse stemming from decades past.
Theodore McCarrick, who preceded Wuerl as archbishop of Washington from 2001 to 2006, stepped down last month from the College of Cardinals, becoming the first cardinal in history to resign because he was accused of sexual abuse.
The report of nearly 1,400 pages covers a period of 70 years into the past, including information from the early 2000s, a time when news of the clerical sex abuse scandal erupted in the US.
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.
Pennsylvania Attorney General Josh Shapiro held a press conference Monday to discuss the report.
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.
Clarify penalties for a continuing failure to report child abuse. Some, such as the Diocese of Harrisburg, made its list public August 1, updating it August 6, adding the name of an accused priest to it after receiving "additional information". Some redactions remain in the final report because the Pennsylvania Supreme Court is still reviewing the appeals by those named in the report.
A couple of dioceses made a decision to strip the accused of their anonymity ahead of the report and released the names of clergy members who were accused of sexual misconduct.
The grand jury said dioceses did not conduct genuine investigations with properly trained personnel, but assigned fellow clergy to ask questions and make credibility determinations "about the colleagues with whom they live and work".