The comment comes in a key pretrial hearing Monday before the March trial of a high-ranking church official, a priest and an ex-priest.
Monsignor William Lynn is charged with conspiring with priests and church officials to keep accused priests in ministry and parishioners in the dark.
To prove a conspiracy, prosecutors want to tell jurors about dozens of priests accused in a 2005 grand jury report. No charges were filed.
Defense lawyers say those allegations shouldn't be aired in the current case.
Donna Farrell, a spokeswoman for the archdiocese, says the church can't comment on the "co-conspirator" comment because of a gag order.
