Fifteen years before the clergy sex abuse scandal came to light, Archbishop Roger M. Mahony and a top advisor plotted to conceal child molestation by priests from law enforcement, including keeping them out of California to avoid prosecution, according to internal Catholic church records released Monday.

The archdiocese’s failure to purge pedophile clergy and reluctance to cooperate with law enforcement has previously been known. But the memos written in 1986 and 1987 by Mahony and Msgr. Thomas J. Curry, then the archdiocese’s chief advisor on sex abuse cases, offer the strongest evidence yet of a concerted effort by officials in the nation’s largest Catholic diocese to shield abusers from police. The newly released records, which the archdiocese fought for years to keep secret, reveal in church leaders’ own words a desire to keep authorities from discovering that children were being molested.

In the confidential letters, filed this month as evidence in a civil court case, Curry proposed strategies to prevent police from investigating three priests who had admitted to church officials that they abused young boys. Curry suggested to Mahony that they prevent them from seeing therapists who might alert authorities and that they give the priests out-of-state assignments to avoid criminal investigators.