By Richard Allen Greene, CNN

(CNN) - As a young man studying for the priesthood, Patrick Wall imagined life as a professor and football coach at a Catholic university.

It didn't work out that way. Two decades later, Wall has not only left the Catholic Church, he has become one of its most tireless opponents.

He's an ex-priest, driven from ministry by the feeling that his superiors used him to help cover up sex abuse by other clergymen.

And he's using the training he gained as a priest to work with victims of abuse who want to take the church to court.

Since 1991, Wall says he has consulted on more than 1,000 abuse cases, helping lawyers pick apart defenses mounted by dioceses from Alaska to Australia.

Now a senior consultant at the law firm of Manly and Stewart in Southern California, Wall spoke to CNN on the sidelines of a recent conference for legal and religion scholars at Cardiff Law School in Wales.

In Philadelphia, where four priests and a Catholic school teacher were indicted on sex abuse charges earlier this year, Wall says he is helping the district attorney build an unprecedented criminal case not only against the clergy, but against an archdiocesan official who supervised them. The priests – one of whom is the church official – and the teacher have denied the allegations.

The case is potentially historic. Wall doesn't know of another case where a U.S. prosecutor has gone after an official at the top of the church hierarchy as well as the suspected abusers themselves.

Prosecutors are trying to convict a vicar – the man who supervised the priests in the archdiocese – with child endangerment because they say he allowed suspected abusers to have contact with young people.

The case raises the possibility that a high-ranking church official will end up behind bars.

Wall hopes the threat of prison time will change the way American bishops respond to abuse allegations in a way that civil lawsuits have not.

"In the civil cases, we have taken over $3 billion, but you're not getting a lot of change in the system," he says.

There has been more than a decade of intense focus on abuse by priests across the United States and Western Europe, plus lawsuits, investigations, and Vatican statements, including instructions to bishops around the world just last month to come up with an abuse policy.

And even so, Wall says, priests are still abusing children.

"I'm working on stuff that happened in the summer of 2010," he says. "It's the same old sodomy."

A life-changing assignment

Wall was studying to be a priest at Saint John's Abbey in Collegeville, Minnesota, when there was a life-changing knock on his door one morning after breakfast.

At his door that day in 1990 was the head of the abbey, Abbot Jerome Theisen, with an assignment, Wall says.

Wall, then 25, was to move into one of the freshman dormitories at the university associated with the abbey. The abbot wanted him to become a faculty resident, a staff position that involved keeping an eye on first-year university students in college housing. He was to make the move immediately, that very morning.

Wall knew why.

"Starting in 1989, we started getting hit with lawsuit after lawsuit" from people alleging that priests had abused them, Wall says. He says the abbot told him that credible abuse accusations had been made against the man Wall was to replace.

Brother Paul Richards, a spokesman for Saint John's Abbey, said that the monastery and university had no record of why Wall was asked to work in the dorm. Abbot Theisen has died, Richards added.

Saint John's Abbey adopted a policy on sexual abuse and exploitation in 1989, it says on its website, saying that made it “among the first institutions to adopt” such a policy.

Wall, for his part, says the abbot's request put him on the road to becoming what the church unofficially calls a "fixer," a person who parachutes in to replace clergy who have to disappear quickly and quietly.

One of Theisen's successors, Abbot John Klassen, issued an open letter of apology in 2002, saying that "some members" of the monastic community had engaged in "abusive sexual behavior with people in our schools and parishes."

A lawsuit was filed earlier this month against Saint John's by a man who says he was abused in the 1960s by a priest who later served as abbot between Theisen and Klassen. The abbey says it was “shocked” by the charges against the late Abbot Timothy Kelly, who died of cancer last year.

It says it is investigating the claims against Kelly, calling them “the first allegations that Abbot Kelly violated his vows or was an abuser.”

Wall plans to testify in that case, he told CNN.

"In the fall of '92 we had another 13 [abuse] cases come through," Wall says. "They pushed up my ordination" by a few months, Wall says, so he could step into the shoes of another priest who had to vanish.

Understanding the damage

It was after his ordination, Wall says, that he began to understand the trauma that abusive priests were inflicting, not only on their victims but on victims' families and communities.

As a new priest, Wall started hearing confessions of victims' relatives who blamed themselves for the abuse, telling Wall "I should have known, I should have seen the signs."

A heavy-set man who laughs easily, Wall still looks like the linebacker he was in high school and college. He peppers his speech with words like "dude" and casually refers to people who he thinks have done something stupid as "morons."

But relating the confessions of victims' relatives, Wall's cheerful demeanor hardens.

"I'm telling them, 'You haven't committed a sin,'" he says.

Wall says that child abuse isn't like other injury cases, such as car crashes, in which a victim might be 10% at fault. Instead, he says, "100% of the blame is on the perpetrator."

Over the next four years, Wall says that the Archdiocese of Saint Paul and Minneapolis sent him to four more places in Minnesota where priests needed to move out fast.

He learned a lot. Wall says he saw that there was a budget for handling cases of priestly sexual abuse as far back as 1994, eight years before the scandal blew up nationally with revelations about abuse in Boston, Massachusetts. The archdiocese could not immediately confirm that, but spokesman Dennis McGrath said he would not be surprised if it was true, saying the archdiocese had been a leader in helping victims of abuse.

Wall did what the church told him to do for as long as he could, he says, but his doubts continued to grow.

"I followed the party line," he says. "But it's pretty hard to follow the party line when you don't think the party line is moral any more."

The breaking point came in 1997. Wall was in Rome, studying for a master's of divinity degree. His abbot called from Minnesota to tell him he was being posted to the Bahamas.

It was not the dream job it might sound like.

Wall says that the Bahamas was where Saint John's was sending priests it had to keep away from people because of abuse allegations. Richards, the abbey's spokesman, flatly denies the charge.

"I basically was going to be a prison warden," Wall says.

"Without much planning, I said, 'Basta cosi,'" he says, lapsing into Minnesota-accented Italian meaning, "Enough of this." Wall had decided to leave the priesthood.

The abbot did not take that well, Wall says, warning that he would never make it in "the real world," that he would not be released from his priestly vows and that the order would bill him for the master's degree it had sponsored for him. The tab for the degree was about $48,000, he says.

Richards denies those allegations. "It has never been the abbey's practice to require payback for education from members of our community who have left," he says, "and it was not the case with Pat Wall."

Wall says the abbot's threats did not change his mind.

"All it did is piss me off even more," he says. "I left without a plan in December 1997."

Insider knowledge

Wall says he went home to Lake City, Minnesota to live with his parents, then bounced from job to job for nearly five years. He got married and had a daughter. He made good money as a salesman in Southern California but says he found the work as intellectually stimulating as "shovelling dirt."

And then, in 2002, the California state legislature did something that would change Wall's life. The state opened a one-year window to allow victims of clergy abuse to sue the church, even if the if the statute of limitations on the case had already expired.

Wall's eyes light up as he discusses the moment.

The law did not specifically target the Catholic Church, Wall says, noting that some rabbis were sued as well. But Catholic organizations were by far the largest group of defendants.

Still, suing a Catholic diocese was no easy task. "The litigation demanded a level of expertise that had never been needed before," Wall says.

Because of his religious training in canon law, as the Catholic Church's rules are known, Wall had that expertise. He knew how and where the church kept records. He knew where money came from and where it went. He spoke Italian and Latin.

In his first case, he testified against the Roman Catholic Diocese of Orange, California, challenging its claim that it did not know the Franciscan friar at the center of abuse allegations.

Wall insisted that the archdiocese and any priest in it would have easy access to church records saying who the Franciscan was and who had jurisdiction over him.

The case settled out of court, Wall says.

The Diocese of Orange declined to comment for this article, as did the Archdiocese of Los Angeles, which is the defendant in several cases currently involving Wall’s firm, Manly and Stewart.

Jeffrey Lena, a lawyer who represents the Vatican in the United States, also declined to comment.

But Jeff Anderson, a Minnesota-based lawyer who specializes in suing the Catholic Church on behalf of abuse victims and filed the suit against Saint John's Abbey, is full of praise for Wall.

Anderson calls Wall “an extraordinary researcher, academic and hands-on voice of experience from the inside.”

He praises the former priest's “courage,” and says he is a “powerful, insightful source of information based on his own personal experience and his study of the phenomenon” of abuse.

An old problem

Wall argues that the problem of abuse by priests is far older than anyone in the church admits publicly.

The earliest church records concerning sexual misconduct by priests come from the Council of Elvira, he says. That synod took place in what is now Spain in the year 309.

There was a treatment center for abusive priests in Hartford, Connecticut, as far back as 1822, Wall says, and the Vatican issued instructions to American bishops on how to judge and punish accusations of criminal acts by priests as far back as 1883.

Wall provided his translation of the 1883 instructions to CNN. They do not refer to any specific crimes, but refer to “abuses” and “evils.” They set out how to investigate, judge and punish crimes by priests, laying out rules such as the examination of witnesses in private, and the opportunity for the accused to know the charges and to respond and appeal.

The Philadelphia district attorney's office declined to comment on assistance it is receiving from Wall, saying it was prevented by court order from discussing the case with the media.

But Wall says that years of seeing how the Catholic Church handles abuse cases have convinced him that the church will not solve the problem itself.

He says he's not impressed by new instructions from Rome last month giving bishops around the world a year to come up with procedures for handling allegations of abuse.

"It's a Circular Letter," he says, using the official church term for the document. "That means it's for the circular file. Bishops are going to throw it away."

Last week, the U.S. Conference of Catholic Bishops revised its 2002 charter around dealing with sex abuse allegations to reflect the Vatican's new standards.

Wall believes the Catholic Church will survive this scandal.

"It's going to fix itself," he says.

"The institution is going to become radically smaller" as people abandon the church, he predicts. "The loss of membership, the problems in the criminal courts, the statements from the pope - these are all good."

Perpetrators need "access, power and money" in order to commit crimes and get away with them, Wall argues. A smaller, weaker Catholic Church won't be able to provide those things, making it less of a haven for abusers, he says, which will lead to a cleansed institution.

In the meantime, Wall says, the church should give up trying to handle abusers internally and let the law step in.

He recommends that the church "completely get out" of child protection, hand over all its files to civil law enforcement, and make bishops sign a legal oath every year that there are no perpetrators in the ministry - which would open them to criminal prosecution if they are found to have lied.

"Otherwise," he says, "I'll be prosecuting priest sex abuse cases for the rest of my life."