Thomas R. Duvall, one of the most violent sex offenders in state history, is one step closer to being released after spending more than 30 years locked up for a series of brutal rapes of teenage girls.

In a ruling issued Monday, a three-judge panel of the Minnesota Court of Appeals upheld a lower-court ruling in favor of Duvall’s petition for conditional discharge from the Minnesota Sex Offender Program (MSOP). The judges determined the state failed to prove “by clear and convincing evidence” that Duvall did not meet the standards for provisional release into the community.

Human Services Commissioner Emily Piper, whose agency oversees the sex offender program, has already vowed to appeal the ruling to the Minnesota Supreme Court, setting the stage for another round of legal arguments over Duvall’s future.

“I have grave concerns about this decision,” Piper said in a written statement. “Three experts have previously testified that Thomas Duvall is not ready for life in the community and that he presents far too great a risk to public safety. I share that view and will exhaust every possible avenue of appeal.”

The ruling upholding the release of Duvall, who has admitted to more than 60 victims, signals a shift in the way courts and the state are handling dangerous sex offenders.

Minnesota is one 20 states that operates a separate system for sex offenders known as civil commitment, in which hundreds of men who have committed violent sex crimes are confined indefinitely in prisonlike treatment centers after they have already completed their prison sentences. The system has been criticized in recent years for locking up too many offenders for too long, and state judicial panels have been approving a record number for conditional release. In June 2015, U.S. District Judge Donovan Frank ruled the program was unconstitutional, calling it a “punitive system” that violates offenders’ rights to due process and access to the courts.

In response to those concerns, specialists at the MSOP have been more willing to support offenders’ petitions for release, and judicial panels have been less likely to override their professional opinion. To date, just 20 offenders have been provisionally discharged from the MSOP in its more than 20-year history.

In an unusual decision in January, the state’s appeals court ruled that sex offender Kirk Fugelseth no longer required inpatient treatment for a sexual psychopathic disorder and approved him for unconditional release, meaning he would no longer be monitored by the state. The decision was upheld by the Minnesota Supreme Court. Fugelseth, who abused children in three states, was only the second person ever to be fully released from the MSOP in its 24-year history. “Without question, the courts are looking at these cases with a bit more of an open mind than they have in the past,” said Eric Janus, professor at Mitchell Hamline School of Law and author of a book on sex offender laws.

‘Still in shock’

Duvall’s extraordinarily violent crimes — and his repeated attempts to gain release from the MSOP over the past decade — have turned him into a lighting rod for those opposed to releasing offenders back into the community. After a state judicial panel initially approved his provisional release early this year, more than 1,000 Minnesotans — including some of his victims — signed an online petition calling on the state to keep him locked up at the MSOP.

Duvall, now 62, committed his first known sexual offense in 1975, when he and two other males raped a 17-year-old girl. Three years later, he again raped a 17-year-old girl whom he picked up at the Star Fair after promising to drive her home. Within months after being released from prison for that crime, he attempted to force another woman into his car and threatened her with a knife. In 1982, Duvall then raped two girls, ages 14 and 15, while threatening them with a shotgun. Then in 1987, just 12 days after his release from prison, Duvall talked his way into a Brooklyn Park apartment, bound a 17-year-old girl with an electric cord and then repeatedly raped her over a three-hour period while hitting her with a hammer.

Duvall was sentenced to 20 years in prison and was later committed indefinitely in 1991 as a psychopathic personality. He has been in the final stage of treatment at the sex offender program since 2010.

In an interview Monday, the sister of the survivor of the 1987 rape said she and her family remain terrified by the prospect of Duvall’s release. The woman said her sister remains so traumatized by the assault that she changes her telephone number every month and has been unable to work since he petitioned for release five years ago.

“Our entire family is on edge,” said the sister, who asked to remain anonymous to protect her safety. “We are still in shock that the courts would let him out after he’s repeatedly reoffended. There’s just no doubt in my mind that he’s going to reoffend.”

At a five-day trial early last year, attorneys for Duvall urged the court to look beyond Duvall’s violent past and focus on his success in treatment. According to court records, Duvall has gone on more than 100 community outings and had worked at a thrift store for eight years without any incidents of inappropriate behavior. He also complied with his treatment program, and eventually became a mentor to other offenders at the MSOP, according to testimony by MSOP staff. Duvall also attended regular Alcoholics Anonymous meetings and participated in a community support group through Project Pathfinder on sexual boundaries.

State opposes its staff

The case has put the Department of Human Services, which oversees the sex offender program, in the unusual position of opposing members of its own treatment team, who have overwhelmingly supported Duvall’s petition for discharge.

At last year’s trial, three expert evaluators not employed by the MSOP testified that Duvall is not ready for release, arguing that he remains fixated on deviant and violent sexual thoughts despite decades in treatment. One of these experts, Dr. James Alsdurf, a forensic psychologist, described Duvall as a sexual sadist who is “obsessed with sex — most of it violent,” after reviewing Duvall’s personal journals, in which he described violent sexual fantasies.

In the end, the state appeals court panel relied heavily on the testimony of MSOP staff and clinicians, who described him as a model detainee, in its ruling in favor of Duvall’s release. “The evidence in the record supports the [lower court] panel’s decision that Duvall no longer requires treatment in his current setting,” the state appeals court panel said in its ruling.

If the state Supreme Court upholds the ruling, Duvall could be released into the community by this fall. He has already been accepted at Zumbro House Inc. of Woodbury, which provides community housing to sex offenders and others with behavioral problems. Under terms of his provisional discharge plan, he would live under 24-hour surveillance and would be required to wear a global positioning device.

A final decision by the Supreme Court is expected by mid-October.