Hundreds of children were sexually abused over the course of at least 40 years by priests assigned with the Roman Catholic Diocese of Altoona-Johnstown, a Pennsylvania grand jury determined.

Superiors, including at least two bishops, worked to conceal the abuse in an effort to protect the church's image, according to the 147-page grand jury report released Tuesday.

The abuse involved at least 50 priests or religious leaders.

"These predators desecrated a sacred trust and preyed upon their victims in the very places where they should have felt most safe," Pennsylvania Attorney General Kathleen G. Kane said in a statement. "Just as troubling is the cover-up perpetrated by clergy leaders that allowed this abuse to continue for decades."

However, no criminal charges are being filed in the case because some abusers have died, the statute of limitations has expired and, in some cases, victims are too traumatized to testify.

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The report is critical of Bishops James Hogan and Joseph Adamec. Hogan headed the diocese from 1966 to 1986 and died in 2005. Adamec, who succeeded him, retired in 2011.

The Altoona-Johnstown report said Hogan covered up abuse allegations by transferring offending priests, including sending one accused clergyman to a school for boys.

The report said Ademac created a "pay-out chart" to help guide how much victims would receive. Victims fondled over their clothes were to be paid $10,000 to $25,000; those fondled under their clothes or subjected to masturbation, $15,000 to $40,000; those subjected to forced oral sex, $25,000 to $75,000; and those subjected to forced sodomy or intercourse, $50,000 to $175,000.

The U.S. Conference of Catholic Bishops estimates that American dioceses have paid nearly $4 billion since 1950 to settle claims with victims.

Mark Bartchak, the current bishop is not accused of any wrongdoing. He recently suspended a handful of priests named as abusers in the report.

The investigation started a few years ago when the office was asked to review the handling of abuse allegations against an athletic trainer at Bishop McCort Catholic High School. Investigators found a "secret archive" that included more than 100,000 documents regarding the abuse incidents.

"This is by no means the end of our investigation. We will continue to look at this matter and consider charges where appropriate, which is why it is so important for those with information to come forward," Kane said in a release. "At the very least, we must continue to shine a light on this long period of abuse and despicable conduct."