Billy, now 24, alleges he was serially raped by Engelhardt, Shero, and one other priest during the 1997-99 school years, when he was in fifth and sixth grades.
In testimony last week, Billy said the assaults in the church sacristy and Shero's car destroyed his childhood.
Billy and several relatives testified that he changed from a happy, outgoing student to a sullen, withdrawn loner when he graduated from eighth grade.
Billy testified that he went on to be expelled from several secondary schools, began heavy drug use that continued through 2011, and attempted suicide several times.
But McGovern's witnesses, who said they taught Billy from second through eighth grades, recalled no downward-spiraling personality.
Janet McKeever, who taught Billy in eighth grade, recalled him as "outgoing and very enthusiastic about everything."
McKeever said he participated in school activities up until graduation.
Shero's attorney, Burton A. Rose, called Shero's mother and sister to testify in his defense.
Bonita Shero told how her son was born with congenital cataracts and underwent 23 surgeries in his first seven months. Shero said her son is blind in one eye and has limited vision in the other.
Shero said her son excelled in school but endured nonstop bullying by other children because of his thick glasses and poor vision.
Rose has argued that Shero's disability made him an outcast as a child and adult - and the perfect target for rumors that he was a child molester.
In questioning Bonita Shero, Assistant District Attorney Mark Cipolletti elicited a response that Bernard Shero has no hearing problems that might force him to get close to hear someone speak.
Earlier Tuesday, one of the final prosecution witnesses was Susan Gallagher, principal of St. Michael the Archangel parish school in Levittown. Gallagher became principal near the end of Shero's tenure there as a resource room teacher from 2002 through 2008.
On Friday, witnesses testified that Shero was considered "odd" and got close to students and touched them when he spoke to them.
Gallagher said Shero was a good teacher and was consistently rehired at the school.
But Gallagher also testified that she eventually was forced to order Shero to have no physical contact with any student, and barred him from taking candid schoolyard photos of children and from inviting any children into his home.
Contact Joseph A. Slobodzian at 215-854-2985, email@example.com, or @joeslobo on Twitter.