The Catholic Archdiocese of Baltimore covered up decades of child sexual abuse by priests and other church leaders dating as far back as the 1940s, the Maryland Attorney General’s Office has claimed in a damning report following a four-year investigation.

More than 600 children were sexually abused at the hands of over 150 clergy, nuns, seminarians and deacons, according to the report, which was released on Wednesday. The investigation alleged an “incontrovertible history” of “pervasive, pernicious and persistent abuse,” which was allowed to continue as diocese officials chose to safeguard the institution rather than protect the children in their congregations and schools.

“This report illustrates the depraved, systemic failure of the archdiocese to protect the most vulnerable – the children it was charged to keep safe,” Attorney General Anthony Brown said in a statement. The report noted that the “sheer number of abusers and victims, the depravity of the abusers’ conduct and the frequency with which known abusers were given the opportunity to continue preying upon children are astonishing.”

In fact, the abuse was allegedly so pervasive that some churches and schools had more than one offender on staff at the same time. A parish in Catonsville, Maryland, had 11 separate abusers between 1964 and 2004.

The archdiocese, the oldest Roman Catholic diocese in the US, didn’t protect victims when allegations of abuse surfaced, according to the state report. For example, when learning in 1987 that a clergyman had sexually abused a 14-year-old girl and admitted to being “aroused by some young girls,” the diocese told the victim that he would be given therapy and reassigned away from children. The diocese took no other action until additional victims came forward in 1994. By then, the report said, nine other girls had been abused, and there were indications of other victims who chose not to report their cases.

The probe focused on abuse prior to 2002, when a bombshell media report on the coverup of sexual abuse allegations by the Archdiocese of Boston led to reforms by the church, including lifetime bans of offenders. However, the attorney general’s office claimed that the Archdiocese of Maryland failed to fully implement needed reforms. For instance, it failed to publicly list all of the abusers it knew about and allowed some to retire with pensions, rather than be ousted.

The report recommended eliminating Maryland’s statute of limitations for claims of childhood sexual abuse, allowing victims to file civil lawsuits for their damages. State lawmakers passed such legislation on Wednesday, approving a bill that would end the current restriction barring alleged victims from suing after they reach age 38.