How long should culpability last?

The peculiarity of the episode - a Roman Catholic bishop indicted on child-rape charges, and a prosecutor dismissing those charges hours later - is typical of the hurdles and complexity of trying sexual-abuse cases.

The events in Springfield, Mass., where retired Bishop Thomas Dupre is accused of molesting two boys in the 1970s, were a blow to victims' advocates, who had looked forward to the first prosecution of a Roman Catholic prelate as a landmark step in the sexual-abuse scandal that erupted in 2002.

The circumstances also highlight a larger debate over sexual abuse and justice. The charges against Bishop Dupre, like so many recent allegations against clergy, date back decades, and because of statutes of limitations, are beyond legal reach. The case has renewed attempts in Massachusetts to end those time limits in an effort, say advocates, to protect future victims and those who have yet to come forward.

But some argue that such statutes provide vital protection against verdicts based on insufficient evidence: As the years go by, ever fewer witnesses are alive or available to testify, and the clarity of events may fade. What's more, many suspect that the worst wave of cases has already passed - that abuse in churches, schools, and other organizations peaked in the 1970s and was more a sign of the era than a sign of things to come.

"Advocacy groups say that [the peak in the 1970s] is due to that fact that it takes a long time for people to come forward," says Thomas Plante, a professor of psychology at Santa Clara University. "We disagree with that. There was a confluence of events in the 1970s.... There is remarkable evidence [to suggest that] there was something particular about the era."

The indictment charging the former leader of the Springfield diocese was unsealed Monday. That afternoon, Hampden District Attorney William Bennett announced he was prohibited from pursuing charges because the statute of limitations had run out long before. (Currently, it can be up to 15 years in Massachusetts; it was six in this case, due to when the alleged abuse occurred.)

The plaintiffs' lawyer, Jeffrey Newman, says Dupre may face charges in other states, since he allegedly traveled outside Massachusetts with the boys. Under certain state provisions, if a suspect leaves a state in which he or she committed a crime, the clock on the statute of limitations stops until he or she returns to that state. Mr. Bennett said he is handing information to authorities in New Hampshire, New York, and Canada.

Still, many local advocates were disappointed and dismayed. "The way events unfolded, it gave us a sense of sudden hope that some prosecutor somewhere was going to follow through and pull it off," says Peter Pollard, the western Massachusetts coordinator of the Survivors Network of Those Abused by Priests. "[The case] really symbolized that this is an issue that permeated the entire structure of the church."

His group was among those lobbying outside the Boston Statehouse Wednesday, calling for an abolition of the state's statute of limitations. Statutes vary by state and crime. Murder has no limitations, and some states have no limits for rape cases involving children, says Patrick Noaker, a lawyer in Minnesota who represents abuse victims.

"Most states are lengthening their statutes of limitations for childhood sexual-abuse cases," he says. Missouri, Illinois, Connecticut, and California have recently extended theirs, though others, including Minnesota and Florida, have not - in part, say experts, because a strong church lobby often wishes to protect church leaders from trials.

Abolishing statutes would raise constitutional questions, says Dr. Plante. He says he understands advocates' frustration. "But in many of these cases, so many years go by [that] there are fewer witnesses, less data, there is psychiatric illness among some of the parties involved. What do you do with that?"

Carmen Durso, a Boston lawyer who represented many plaintiffs in the Boston archdiocese case, says those fighting for the abolition of statutes are not seeking retroactive justice, but are looking toward the future. "Survivors just want to make [sexual abuse] stop," he says.

According to a report by the John Jay College of Criminal Justice, most of the incidents of abuse by clergy reported so far occurred in the 1970s. But Karen Terry, who helped research the report for the United States Conference of Catholic Bishops, says only 10 percent of victims report abuse in the year it occurred. Still, she expects fewer reports of abuse during the 1990s.

In the meantime, many theories have surfaced: Some cite a groundswell of seminarians and priests in the era during the 1970s, an overall mistrust of authority, which may have led to less accountability, or the sexual revolution sweeping the country.

"The changing culture in the 1960s and 1970s had some role to play in this kind of thing," suggests David Finkelhor, director of the Crimes against Children Research Center at the University of New Hampshire. The sexual revolution may have steered some homosexuals to the ministry as a way to control temptations that had been, up to that point, suppressed by societal mores. He also says that many who'd taken vows in a previous era could have been affected by the general change in culture.

Plante says other contributing factors include an absence of checks and balances as a disdain for authority emerged: "In society in general, there was a flatter organizational chart." Indeed, he says, research has shown that the 1970s was a peak time for sexual abuse in many professions, including psychotherapy and schools. Noaker - and many abuse victims - refute such theories; he says predators will prey on the vulnerable regardless of changes in the culture at large.

Things have changed in another way since the 1970s, and partly in response to cases like these. Many experts anticipate far fewer allegations of abuse in the late 1990s, as parents grew more attuned to inappropriate behavior and warned their children of it, and, more recently, as public scrutiny of the Church has grown.

The earlier eras were permeated with "a really trusting Catholic subculture," says John McGreevy, a history professor at the University of Notre Dame. "Priests were worshiped as heroic figures; parents were incredibly trusting with their young boys. Now that trust is gone."