Roman Catholic Church's William Lynn, who was the first US Church official to be convicted in a criminal court for covering up sex abuse claims, has had his child endangerment conviction reversed its decision by the Philadelphia Court of Appeals, BBC News reported.

Monsignor Lynn had be serving three to six years in prison. 

The "unanimous decision released Thursday by the state Superior Court also dismisses the criminal case against Monsignor William Lynn," Fox News reported.

Prosecutors argued Lynn reassigned predators to new parishes in Philadelphia when he was secretary for clergy from 1992 to 2004. He was in charge of supervising about 800 priests, accordiing to news reports. 

"Lynn's conviction stems from the case of one priest, Edward Avery, found to have abused a child after such a transfer," Fox News also reported.

The court said it had not been proven Lynn acted with "intent of promoting or facilitating the crime," according to records.

The appeals court rejected the prosecutors' argument that Monsignor Lynn had supervised the welfare of any particular child.

"He's been in prison 18 months for a crime he didn't commit and couldn't commit under the law,'' Lynn's lawyer said, according to the BBC.