Alarmed by the proposed release of a violent serial rapist, a growing chorus of public officials are calling for harsher prison terms and the abolition of Minnesota’s controversial system of treating sex offenders outside the correctional system.

An unlikely assortment of legislators and law-enforcement officials — on both sides of the political aisle — has expressed concern over the proposed provisional discharge of Thomas Duvall, 58, from the Minnesota Sex Offender Program (MSOP). Duvall was convicted on three separate occasions of sexually assaulting teenage girls — each time shortly after he was released from prison — in cases with gruesome and violent details.

The highly charged recommendation to release Duvall, which still must be reviewed by a panel of state judges, has reopened long-standing questions about how long violent sex offenders should be kept behind bars — and about whether public safety would be better served by treating them inside prison, rather than committing them indefinitely to the MSOP centers in St. Peter and Moose Lake.

“We’ve got to scrap this system and start over,” said Rep. Tony Cornish, R-Vernon Center. “A guy who’s done something as horrific as Duvall should be sentenced to prison and treated in prison. No more civil commitments.”

Hennepin County Attorney Mike Freeman echoed the view, saying therapy for dangerous sex offenders would be more effective and less expensive if conducted in prison.

“If you have to prove that you’re OK to get out [of prison], then these cowboys will line up for treatment like nobody’s business,” Freeman said.

On Friday, a panel of three state judges will hear arguments on whether to hold an in-depth hearing, similar to a trial, on Duvall’s provisional release from the sex offender treatment program. Lawyers for Minnesota Attorney General Lori Swanson will argue against his discharge, saying “fantasy logs” kept by Duvall show that he is still preoccupied with sexually violent encounters.

A number of public officials say the Legislature should mandate tougher sentences for repeat, violent sex offenders like Duvall, and scrap Minnesota’s 18-year-old system of civilly committing the most dangerous sex offenders to indefinite confinement in the MSOP.

Cornish, Freeman and state Public Defender John Stuart all recommend that the state implement indeterminate sentences for serious offenders — with release conditioned on proven completion of intense treatment in prison.

Human Services Commissioner Lucinda Jesson, whose agency oversees the MSOP, said the Legislature should examine the issue, taking into consideration both the prison system and the MSOP. “We need to be looking at this as a whole to make sure we’re doing a better job,” Jesson said.

The number and horrific nature of Duvall’s assaults on teenage girls has some questioning how such a violent offender could be considered for release. In 1978, Duvall was convicted of raping a 17-year-old girl to whom he gave a ride home from the State Fair. He pleaded guilty to third-degree criminal sexual conduct. Five months after he was paroled, in 1981, he attempted to force a woman into his car at knifepoint. Three days after his release for that crime, Duvall assaulted a 15-year-old girl on her way to school; later that day, he sexually assaulted two other girls ages 14 and 15, threatening one of them with a shotgun while he repeatedly raped her. Then, in 1987, just 12 days after his release from prison, Duvall sexually assaulted a 17-year-old girl, hitting her with a hammer while raping her.

An internal panel at the state Department of Human Services has recommended provisional discharge for Duvall — meaning supervised living at a secure community residence — saying he has completed all required treatment. Human Services Commissioner Jesson agreed with the recommendation but has also agreed to have an independent expert examine Duvall again before his final discharge hearing.

Sentences got tougher

Duvall’s crimes occurred just before a string of high-profile parking ramp murders of women in Minneapolis in 1988, which prompted lawmakers to lengthen the sentences for violent sexual offenses. Then the 2003 kidnapping and murder of college student Dru Sjodin by a convicted sex offender provoked a further toughening of sentences, including a rarely used life sentence option for repeat violent offenders. The average prison sentence of convicted sex offenders in Minnesota has more than doubled since 1988, to nearly 11 years.

Retired Judge Franklin Knoll, who heard Duvall’s 1987 case and sentenced him to just 20 months, said he was confined by the more lax sentencing guidelines of the time. Knoll called Duvall’s crime “heinous” and added: “If I had total freedom to impose a sentence, I probably would have put him away for a longer time. … I would be concerned about Duvall, about whether the security is sufficient,” Knoll said.

The state’s prison system would not have to reinvent the wheel to provide therapy: The Department of Corrections estimates that it already provides treatment to many of the 3,000 sex offenders housed in Minnesota prisons.

In addition, the annual cost of housing an inmate in a Minnesota prison is less than one-third of the $120,000-a-year cost of treating an offender in the MSOP, according to a March 2011 report by the Office of the Legislative Auditor.

Surprisingly, even some convicted sex offenders said they would prefer treatment in prison over commitment to Moose Lake or St. Peter, which has become a de facto life sentence because almost no one is ever released. Duvall would become only the second person in nearly two decades discharged from the MSOP.

Currently, convicted sex offenders can spend years in prison and then discover near the end of their term that they are committed indefinitely to the sex offender program. To many offenders and their advocates, a civil commitment essentially amounts to “double jeopardy” — having to serve separate terms behind bars for the same offense.

Michael Rygh, 27, a convicted sex offender, spent three years at the state prison in Moose Lake after pleading guilty to criminal sexual conduct.

Rygh said he was less than 72 hours from being released under supervised conditions when a prison caseworker informed him that he was being committed to the MSOP. Rygh said he would have participated in therapy while in prison but was told that his case was not “high priority” enough.

“I was devastated,” said Rygh, who said he had already lined up a job upon release. “I had my whole future ahead of me and then it was taken away.

“If it’s possible, the person should be treated in prison,” he said. “That’s the time for the harm and the pain you’ve caused. … To say you have to stay longer, that’s frustrating because I wasn’t sentenced to that.”