Around 300 Roman Catholic priests have molested more than 1,000 children - and possibly many more - in Pennsylvania since the 1940s, a US grand jury report has revealed.
The report also accused senior church officials of systematically covering up complaints in the state.
The "real number" of abused children and abusive priests might be higher since some secret church records were lost and some victims never came forward, the grand jury said.
US bishops adopted sweeping reforms in 2002 when abuse by clergymen became a national crisis for the church. These changes included stricter requirements for reporting accusations to law enforcement and a streamlined process for removing clerics who abuse children.
However, the grand jury said more changes are needed.
In its 900-page report, the grand jury wrote: "Despite some institutional reform, individual leaders of the church have largely escaped public accountability.
Top church officials have mostly been protected and many, including some named in the report, have been promoted, the grand jury said. The report concluded that "it is too early to close the book on the Catholic Church sex scandal".
In nearly every case, prosecutors found that the statute of limitations has run out, meaning that criminal charges cannot be filed.
More than 100 of the priests are dead. Many others are retired or have been dismissed from the priesthood or put on leave.
Authorities charged just two as a result of the grand jury investigation, including a priest who has since pleaded guilty, though some of those named had been charged years ago.
Attorney general Josh Shapiro said the investigation is ongoing.
The investigation of six of Pennsylvania's eight dioceses - Allentown, Erie, Greensburg, Harrisburg, Pittsburgh and Scranton - is the most extensive investigation of Catholic clergy abuse by any state, according to victims' advocates. The dioceses represent about 1.7 million Catholics.
Until now, there have been just nine investigations by a prosecutor or grand jury of a Catholic diocese or archdiocese in the United States, according to the Massachusetts-based research and advocacy organisation, BishopAccountability.org.
The Philadelphia archdiocese and the Johnstown-Altoona diocese were not included in the investigation because they have been the subject of three previous scathing grand jury investigations.
The grand jury heard from dozens of witnesses and reviewed more than half a million pages of internal diocesan documents, including reports by bishops to Vatican officials disclosing the details of abusive priests that they had not made public or reported to law enforcement.
The panel concluded that a succession of Catholic bishops and other diocesan leaders tried to shield the church from bad publicity and financial liability.
They failed to report accused clergy to police, used confidentiality agreements to silence victims and sent abusive priests to so-called "treatment facilities" which "laundered" the priests and "permitted hundreds of known offenders to return to ministry," the report said.
The conspiracy of silence extended beyond church grounds. Police or prosecutors sometimes did not investigate allegations out of deference to church officials or brushed off complaints as outside the statute of limitations, the grand jury said.
Diocese leaders expressed sorrow for the victims, stressed how they have changed and unveiled, for the first time, a list of priests accused of sexual misconduct.
James VanSickle of Pittsburgh, who testified he was sexually attacked in 1981 by a priest in the Erie Diocese, called the report's release "a major victory to get our voice out there, to get our stories told".
The report is still the subject of an ongoing legal battle, with redactions shielding the identities of some current and former clergy named in the report while the state supreme court weighs their arguments that its wrongful accusations against them violates their constitutional rights.
It is also expected to spark another fight by victims' advocates to bring about changes in state law that congress members have resisted.
Its findings echoed many earlier church investigations around the country, describing widespread sexual abuse and church officials' concealment of it.
US bishops have acknowledged that more than 17,000 people nationwide have reported being molested by priests and others in the church going back to 1950.