One by one, the assistant district attorneys walked to a courtroom lectern Monday to tell, at times explicitly, different versions of what sounded like the same story: priests molesting children, and Archdiocese of Philadelphia leaders failing to act on claims or signs of abuse.

One cited testimony from altar boys who said the former Rev. Edward Avery got them drunk in the 1970s, then proposed to "sober them up" by rubbing ice on their genitals.

Another detailed more than a dozen abuse claims against Nicholas Cudemo, who was shuffled among parishes and high schools over decades before he was defrocked.

A third said church leaders left the Rev. Michael Murtha in ministry for years after allegedly finding a cache of child pornography and a sexually graphic "fantasy letter" he had written to a boy in his Northeast Philadelphia parish.

None of the allegations was new; prosecutors acknowledged that some were decades old and unproven.

But they offered them in a bid to convince Common Pleas Court Judge M. Teresa Sarmina that jurors in the looming sex-abuse and conspiracy trials of four current and former priests cannot properly weigh the crimes unless they also hear about decades of abuse and cover-up.

That is the only way, Assistant District Attorney Patrick Blessington told Sarmina, "for the jury to get the complete picture."

The clash over the old cases has become the central battle in the prosecution of Msgr. William J. Lynn, the former archdiocesan administrator who last year became the first church official in the nation arrested and charged with covering up or enabling child-sex assaults by priests.

Prosecutors charged Lynn, 61, with conspiracy and endangerment. They say that as secretary for clergy, he recommended parish assignments for Avery and another priest, the Rev. James J. Brennan, in the 1990s despite knowing or suspecting that they had abused children. Avery and Brennan later molested boys in their parishes, a grand jury concluded last year.

The defendants have pleaded not guilty and denied any wrongdoing. Jury selection is scheduled to begin Feb. 22, with opening statements a month later.

Lynn's attorneys, who are being paid by the archdiocese, repeatedly argued that he is unfairly being made a scapegoat for the church's wider failings on clergy sex abuse.

Attorney Thomas Bergstrom called the prosecution's attempt to introduce the case files of Murtha, Cudemo, and 25 other priests not charged in the case "nutty" and "dangerous."

Nearly all the cases involved claims of abuse that happened years before Lynn became secretary of clergy under Cardinal Anthony Bevilacqua in 1992 or came to light after he left the job in 2004, Bergstrom said.

"They want to put all this evidence in, even knowing - even conceding - that he didn't know about this," he told Sarmina, later adding, "What was he supposed to do, divine these things?"

Prosecutors want to introduce the evidence under trial rules that allow jurors to hear past evidence of a defendant's bad acts if that conduct can explain his motives, knowledge, intent, or a pattern.

They cited memos and testimony that they said showed Lynn and others repeatedly chose to ignore signals of child sex abuse and failed to alert parishioners and police when they suspected or identified abusive priests.

"It was a willful blindness, your honor," Assistant District Attorney Mark Cipolletti said. "He turned a blind eye to this."

Lynn sat silently, flanked by his relatives and a lawyer for much of the five-hour hearing, one row behind Brennan.

Avery did not attend, though the first part of the hearing focused solely on his conduct.

Cipolletti recounted accusations from seven former altar boys, including some who came forward after Avery was defrocked in 2006 and became the subject of a grand jury investigation.

Also missing from the hearing was the fourth defendant, the Rev. Charles Engelhardt, who is accused of molesting the same boy at St. Jerome Parish in Northeast Philadelphia who prosecutors say was abused by Avery.

Engelhardt's attorney, Michael McGovern, left the courtroom after a closed-door meeting with the judge, which a source close to the case said signaled Engelhardt might be tried separately.

McGovern had argued that Engelhardt should not be tried with the others because their case is about a broader archdiocese conspiracy and he belongs to an independent religious order, the Oblates of St. Francis.

McGovern could not be reached after the hearing and previously has refused to discuss the case, citing a gag order from the judge.

The hearing is scheduled to resume Tuesday morning.

Contact staff writer John P. Martin at 215-854-4774, jmartin@phillynews.com, or @JPMartinInky on Twitter.