Thomas Duvall was convicted of a series of brutal rapes of teenage girls in the 1970s and has admitted to more than 60 victims. (Star Tribune/The Minnesota Star Tribune)

Thomas Ray Duvall, a serial rapist who has spent more than 30 years locked up for a series of violent rapes of teenage girls in the 1970s and 1980s, has been approved for conditional release from the Minnesota Sex Offender Program (MSOP).

In a one-sentence ruling Tuesday, the Minnesota Supreme Court rejected a request by the Minnesota Department of Human Services to review Duvall's petition for conditional discharge, which had been approved in July by an appeals court panel.

The decision brings to a formal close an acrimonious five-year legal battle over the future of Duvall, one of the most violent and high-profile sex offenders in state history.

His case was closely watched as a test of Minnesota's civil commitment system, which confines sex offenders indefinitely after their prison terms end, and whether courts are willing to defy public outrage in determining if a convicted offender poses a public threat.

In this case, the judges acknowledged that Duvall still has a risk of reoffending, given his extraordinarily violent history and pattern of deviant sexual thoughts. Yet those concerns were outweighed by Duvall's model behavior at the MSOP and the opinion of the state's own treatment team, which overwhelmingly supported his petition.

The ruling also signals a shift in the way judges and the state are handling sex offender cases. In June 2015, U.S. District Judge Donovan Frank ruled that Minnesota's sex offender program was unconstitutional, calling it a "punitive system" that violates offenders' rights to due process. Although Frank's ruling was later overturned by a higher court, specialists at the MSOP have been more willing to support offenders' petitions and state judges have been less likely to override them.

At the time of Frank's ruling, only three offenders had been discharged from the MSOP in its 20-year history — a number cited by attorneys and civil rights advocates as evidence that civil commitment was a "de facto life sentence." Now the number who have been granted provisional discharge (or approved for release with certain conditions) has reached 26. Another three offenders have been released without any conditions, which is unprecedented.

"This [ruling] is an example of the professionals and the courts essentially standing up for what the law has always promised — that civil commitment is not punishment … and lasts only so long as an individual poses a very serious danger," said Eric Janus, a professor at Mitchell Hamline School of Law and author of a book on sex offender laws. "It's based on the principle that people can change."

Still, that philosophy got a grave challenge in the case of Duvall, who is diagnosed as a sexual sadist and has admitted to more than 60 victims.

Starting in 2014, the state Attorney General's Office and the Department of Human Services, which oversees the MSOP, have consistently opposed Duvall's release, citing the number and horrific nature of his sexual assaults on teenage girls.

"Out of a deep concern for public safety, I have adamantly opposed and repeatedly challenged this decision at every turn," Human Services Commissioner Emily Piper said in a statement Wednesday. "Ultimately, this was the court's decision, not mine, and I respect that authority."

Once released, Duvall will live with other sex offenders in a secure Twin Cities building operated by Zumbro House, Inc., after neighbors are notified by local police. The exact location has yet to be determined, said Christopher Onken, president of Zumbro House.

Under the terms of his discharge plan, Duvall will receive 24-hour surveillance, wear a global positioning device, undergo random searches and face restrictions on leaving the residence without MSOP staff, among other restrictions. If he violates any of the more than two dozen conditions of his plan, officials said, the MSOP can revoke his discharge and place him back in confinement.

Nonetheless, Wednesday's ruling prompted anger and fear for relatives of one of Duvall's victims, a teenage girl whom he beat and raped repeatedly in 1987. The victim has been so traumatized that she has changed her phone number and address every few months since Duvall's petition for release became public in late 2013.

"We are terrified that he will be walking the streets," said her sister, who asked that her name not be used out of concern for her family's safety. "We feel let down by our elected officials, MSOP and the court system, and now fear for the community at large."

'Obsessed'

Duvall, now 63, committed his first known sexual offense in 1975, when he and two other males raped a 17-year-old girl. Three years later, he raped a 17-year-old girl whom he picked up at the State Fair after promising to drive her home. Within months after his release from prison for that crime, he attempted to force another woman into his car and threatened her with a knife. In 1982, Duvall raped two girls, ages 14 and 15, while threatening them with a shotgun. Then on the day after Christmas 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 for three hours while hitting her with a hammer.

Duvall was then 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 April of 2010.

At last year's trial, three outside evaluators testified that Duvall was not ready for release from the MSOP, arguing that he remains fixated on deviant and violent sexual thoughts despite decades in treatment. One of them, Dr. James Alsdurf, a forensic psychologist, described Duvall as "obsessed with sex — most of it violent," after reviewing hundreds of pages of journals in which Duvall described his sexual fantasies.

In the end, however, the appeals court panel relied heavily on the testimony of the MSOP's own staff, who described Duvall as a model detainee who was committed to his treatment program. Duvall had gone on hundreds of community outings during his years at MSOP, volunteered at a thrift store for eight years, and had completed every phase of treatment in the program — all without an incident of inappropriate behavior, the staff testified.

Members of the judicial panel noted that Duvall continued to experience "intrusive and deviant sexual thoughts," but concluded that he had learned how to manage those thoughts. Duvall testified that he took medication to reduce his sexual preoccupation, and managed his thoughts through therapy and support groups.

Chris Serres • 612-673-4308 Twitter: @chrisserres