A former top aide to Cardinal Anthony J. Bevilacqua, Lynn last month became the first Catholic church official convicted for enabling clergy sex abuse.
In their 29-page brief, the prosecutors told the judge that only the stiffest term would send a message to Lynn and other culpable church leaders.
"A maximum sentence," they wrote, "may be the only way to impress upon the defendant that he committed a serious crime, that there are more important rules to follow than instructions from corrupt or misguided bishops and that the protection of children trumps the reputation of abusers and the institution that harbors them."
Lynn's lawyers say such a harsh term would be unfair and legally flawed.
In their own filing to the judge, they noted that the jury convicted Lynn of a single count, child endangerment, for not removing a former parish priest, Edward Avery, from active ministry after learning Avery had previously molested a teen.
In 1999, Avery sexually assaulted a 10-year-old altar boy at a Northeast Philadelphia church. That victim was one of nearly 20 to testify at Lynn's three-month landmark trial.
Lynn's lawyers say he had no reason to suspect Avery would abuse the boy and was following the recommendations of the hospital psychologists who evaluated him.
They also noted that two-thirds of the defendants convicted of a third-degree endangerment felony in Pennsylvania since 1996 have been spared state prison terms.
Under their calculations of state guidelines, Lynn, a priest for 36 years who has spent a decade under the spotlight, deserves probation or a county jail term of a year or less.
Prosecutors scoffed at the argument. They maintained Lynn has a well-documented criminal history - one that unfolded during weeks of often gut-wrenching trial testimony from witnesses who described being fondled, molested or raped by their parish priests.
As the archdiocesan secretary for clergy responsible for investigating the claims, Lynn saw the impact but did nothing, Blessington and Sorensen wrote.
"He observed first-hand, on a regular basis the destruction of lives as victims of priests whom he supervised poured out their stories of abuse, shame, despair, isolation, anger, loss of faith, addictions, failed marriage and lost lives," their motion states.
Lynn's actions, they said, also had a devastating affect on area Catholics, causing many to question their faith and leaders, and costing the church millions at a time when financial woes are forcing it to close parishes and schools.
"Given all that, the prosecutors argued, "his offense could not be graver. It easily merits the maximum sentence."
Contact John P. Martin at 215-854-4774, firstname.lastname@example.org or @JPMartinInky on Twitter.