Avery, 70, is serving a 21/2- to five-year prison term after pleading guilty to sexually assaulting the same 10-year-old altar boy in 1999 when Avery, then chaplain at Nazareth Hospital, lived in the rectory of St. Jerome's parish in Northeast Philadelphia.
But of more significance to Engelhardt and Shero is the prosecution's allegation that Engelhardt, the parochial vicar at St. Jerome's, first molested the child in 1998 and "passed him along" to Avery and then Shero.
Avery pleaded guilty March 22 - a week before he was to be tried with Msgr. William J. Lynn and the Rev. James J. Brennan in the first trial from the 2011 county grand jury report on the sexual abuse of children by Catholic priests in the Philadelphia archdiocese.
Lynn, 61, who as secretary for clergy from 1992 to 2004 investigated allegations against priests, was convicted June 22 of child endangerment involving Avery's offenses, the first church supervisor in the nation held criminally responsible for another priest's sexual abuse. Lynn is serving a three- to six-year prison term.
The same jury could not decide the case against Brennan, 49, who will be retried March 6 for the attempted rape of a boy, 14, in 1996.
Hints that Avery might become a trial witness first arose last week when he was suddenly transferred from the state prison at Laurel Highlands in Western Pennsylvania to the maximum-security Graterford Prison in Montgomery County.
At Friday's hearing before Judge M. Teresa Sarmina, Avery's lawyer, John P. Donahue, urged prosecutors to decide quickly whether Avery would testify.
"There are some fairly difficult circumstances for living today in Graterford," Donahue said. "You can imagine a 70-year-old person sitting there in Graterford."
Assistant District Attorney Patrick Blessington said he would move Avery soon.
Avery's guilty plea does not require him to cooperate with prosecutors or testify. But he could not invoke the Fifth Amendment protection against self-incrimination because he has already pleaded guilty.
Testifying could benefit Avery when authorities decide whether he should be paroled after serving his minimum prison term.
But Avery's testimony - arguably the first by a defrocked priest and admitted pedophile - could cut both ways.
As damaging as it could be to Engelhardt and Shero, Avery's behavior on the witness stand could also undermine his credibility and hurt the prosecution's case.
Some court observers say the jury's inability to reach a verdict against Brennan may have been linked to his alleged victim's attitude while testifying.
Friday's hearing was necessary because Tuesday's scheduled start of Engelhardt's and Shero's trial was delayed by deaths in a defense lawyer's family.
Sarmina said the delay made it impossible to remain as the judge in the case because she has a series of back-to-back homicide trials through May.
The Oct. 22 trial was transferred to Ceisler. Ceisler, elected in 2007, is the former internal integrity officer for the Philadelphia Police Department.
Sarmina severed the cases of Engelhardt and Shero from those of Lynn, Avery, and Brennan after their lawyers argued that their clients deserved a separate trial because neither had been supervised by Lynn.
Engelhardt, 65, remains a priest but was removed from ministry in 2009. He now lives in a house under the supervision of his independent religious order, the Oblates of St. Francis de Sales.
Contact Joseph A. Slobodzian at 215-854-2985, firstname.lastname@example.org, or follow @joeslobo on Twitter.