Philadelphia (CNN) -- Opening arguments started Monday in the first case in which a Roman Catholic archdiocese official is accused of covering up evidence of suspected sexual abuse of children.
Monsignor William Lynn and the Rev. James Brennan appeared before Common Pleas Judge Teresa Sarmina inside a nearly filled Philadelphia courtroom. The attendees had to pass through a metal detector and surrender all electronic devices before entering the courtroom.
Commonwealth prosecutor Jacqueline Coelho told jurors in her nearly hour-long opening statement that Lynn's role was to protect priests, the church and privacy "at any cost."
Lynn, dressed in all black and wearing a priest collar, listened intently as Coelho argued that he knowingly covered up incidents of sexual abuse, including alleged acts by Brennan, and "ignored common sense and placed children at risk."
Lynn, 61, who served as the secretary for clergy under former Philadelphia Archbishop Anthony Bevilacqua, is charged with endangering the welfare of a child in connection with the alleged assaults.
From 1992 until 2004, Lynn was responsible for investigating reports that priests had sexually abused children.
Brennan, 48, is accused of assaulting a 14-year-old boy in 1996.
Both pleaded not guilty in April.
Their defense attorneys were slated to give their opening statements Monday afternoon.
Last year, a Philadelphia grand jury report accused the archdiocese of failing to investigate claims of sexual abuse of children by priests.
The grand jury report led to the Philadelphia district attorney's office criminally charging four Philadelphia priests and a parochial school teacher with raping and assaulting boys in their care, while Lynn was accused of allowing the abusive priests to have access to children.
Defrocked priest Edward Avery was slated to go on trial with Lynn and Brennan, but he pleaded guilty last week to involuntary deviate sexual intercourse and conspiracy to endanger welfare of child, according to court documents.
Avery was sentenced to two and a half to five years in prison. He is scheduled to report for his sentence on April 2.
The plea agreement does not require Avery to testify against Lynn. Judge Sarmina advised jurors to "keep an open mind" and "not speculate about" Avery's absence.
The Philadelphia scandal could open a historic chapter in the abuse crisis, church watchers say, by changing the way the American criminal justice system deals with church abuse.
The charges are unusual because they go beyond accusations against priests and included a church higher-up charged with covering up the abuse, which church experts say has never happened in the United States before.
Avery and Charles Engelhardt are charged with assaulting a 10-year-old boy at St. Jerome Parish in Philadelphia in 1998 and 1999. Avery was defrocked in 2006.
Bernard Shero, a teacher at the school, is charged with assaulting the same boy there in 2000.
Engelhardt and Shero, who pleaded not guilty to sexual abuse and conspiracy charges in April, are facing sex abuse charges and will be tried separately in September.
Cardinal Bevilacqua, who died on January 31, testified 10 times before grand juries in 2003 and 2004. A final grand jury report said it had no doubt that the cardinal knew about the danger posed by the accused priests and his actions endangered thousands of children in the archdiocese.
Bevilacqua served as archbishop of Philadelphia from February 11, 1988, to October 7, 2003, the archdiocese said in announcing his death. He was elevated to the College of Cardinals on June 28, 1991.
Lynn would face a maximum of 14 years in prison if convicted of all charges, according to the district attorney's office.
After the release of the January 2011 grand jury report, Cardinal Justin Rigali, who later resigned as Philadelphia's archbishop, placed Lynn on administrative leave.
A total of 23 priests in the Philadelphia area have been placed on administrative leave by the archdiocese, 21 on March 7, 2011. The two other priests, who were retired but were allowed to assist in priestly duties, were placed on leave 23 days later.
A gag order imposed by a Philadelphia judge remains in effect. It bars all parties involved in the criminal case from talking to the media.