Brennan, 48, is one of two Philadelphia clerics on trial in Common Pleas Court. He is accused of trying to rape a 14-year-old boy in 1996.
Brennan has denied the allegation, but prosecutors have said they believed the transcript of his canonical trial would undermine that denial.
On Tuesday, Assistant District Attorney Patrick Blessington told Common Pleas Court Judge M. Teresa Sarmina he believed Brennan had admitted the truth of at least some allegations in the church trial.
"Although it wasn't an outright admission of the facts that were alleged, there were statements that were made that were inculpatory in nature," Blessington said.
Although prosecutors have a transcript of the canonical trial, court rules bar them from using it in the criminal case unless Quirk authenticates the document and his words.
Quirk objected to testifying. According to Judge Wilson's four-page order, at a hearing on April 12, Quirk - now judicial vicar and assistant to Bishop Michael Bransfield in the Diocese of Wheeling-Charleston - argued that "he should not be required to return for the trial in Pennsylvania because he is not a material witness for the state and that he is protected by privilege."
Wilson, however, ruled that Quirk was a material witness and that his testimony in Philadelphia was "essential in ascertaining the truth. Also it is, in the court's opinion, probable that Msgr. Quirk's absence could cause the defendants' constitutional rights to confrontation and meaningful cross-examination to be lost."
Wilson ordered Quirk to appear in Philadelphia when requested between April 29 and May 1 and ordered the District Attorney's Office to reimburse him for "all reasonable and necessary expenses."
He also noted that Sarmina had agreed Quirk would be "protected from arrest or civil and criminal process [by Pennsylvania authorities] while traveling and attending the trial."
The legal struggle to bring Quirk to testify took on a higher profile after Philadelphia prosecutors presented testimony that Quirk's boss - Bransfield - was also the subject of allegations of sexual abuse when he was a Philadelphia priest in the 1970s.
Bransfield, 68, a Philadelphia native ordained by the late Cardinal John Krol, has never been charged with sexual abuse and has categorically denied the allegations. But Quirk's resistance to testifying led SNAP - the Survivors Network of those Abused by Priests - to accuse Bransfield of trying to cover up evidence of sexual abuse by priests.
SNAP officials lauded Wilson's ruling but added, "we're still disappointed that it's taking a judge's order to get Catholic officials to do their simple, civic duty - honor a subpoena. The church hierarchy claims it cooperates with law enforcement. But as this case shows, often they only cooperate when a judge insists that they do so."
Bryan Minor, a spokesman for Bransfield and the West Virginia diocese, said it was a matter of following the law: "We needed to have a valid legal process, which we do now have. Accordingly, Msgr. Quirk will appear."
Quirk's testimony could be crucial to prosecutors and damaging to Brennan's defense.
On trial with Brennan is Msgr. William J. Lynn, 61, who, as secretary for clergy of the Philadelphia Archdiocese from 1992 to 2004, was responsible for investigating allegations of sexual abuse of minors by priests. Lynn is the first church official criminally charged with enabling abusive priests or covering up the abuse.
Lynn has denied the allegations.
Contact Joseph A. Slobodzian at 215-854-2985, firstname.lastname@example.org, or follow @joeslobo on Twitter.