Thomas R. Duvall, a serial rapist who has spent the past 30 years locked up for a series of violent sexual assaults in the 1970s and 1980s, has been approved for conditional release from the Minnesota Sex Offender Program (MSOP).

In a decision Monday, a panel of state judges approved Duvall's petition for provisional discharge, ruling that his progress in treatment outweighs his "fearful diagnosis" as a sexual sadist.

"[Duvall] cannot change his past offense history, but he is committed to change in the present and future," according to the 42-page ruling by the state Supreme Court appeals panel.

On Tuesday, however, Human Services Commissioner Emily Piper, who oversees the MSOP, quickly vowed to appeal the panel's decision.

"I, along with three testifying experts in this case, believe that Thomas Duvall poses an exceptional risk to public safety and should not be released into the community at this time," Piper said in a written statement.

Duvall, 62, sparked a political firestorm four years ago when staff from the MSOP recommended him for a conditional discharge after years in detention. Minnesota Attorney General Lori Swanson and others raised alarms about the number and brutal nature of Duvall's sexual assaults, and the controversy prompted Gov. Mark Dayton to temporarily suspend all releases from the program.

In early 2016, Duvall petitioned for release again, winning a hearing before the appeals panel last spring, and therapists and other staff at the MSOP depicted him as a reformed man who was ready to return to the community.

Under a provisional discharge plan, Duvall would live under close surveillance in a halfway house for sex offenders. He would have 24-hour supervision and GPS monitoring, and would not be allowed to leave the residence without an escort.

Serial rapes

The commissioner's challenge comes as the state faces legal pressure to show that it provides genuine therapy and a pathway for release from a treatment program that has long been criticized for detaining too many offenders for too long.

It also sets the stage for another round of arguments over Duvall's future.

His extraordinarily violent crimes, and his repeated efforts to win release, have made him one of Minnesota's most notorious sex offenders. In 1978, Duvall was convicted of raping a 17-year-old girl while giving her a ride home from the State Fair. Five months after he was paroled, in 1981, he attempted to force a woman into his car at knife point. 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. Then in 1987, just 12 days after his release from prison, Duvall bound a 17-year-old girl with an electric cord and repeatedly raped her while hitting her with a hammer.

In an interview Tuesday, the sister of the survivor of the 1987 rape said she and her family were "terrified" by the prospect of Duvall's release.

"This opens a very deep wound," said the sister, who asked that her name not be used. "I am scared for my sister, and I am scared for all the teenage girls out there, that this man will do this to someone else."

A spokesman for Swanson said she was "very troubled" by the panel's decision and supports the commissioner's appeal. "[Duvall] is a sexual sadist with an extraordinary number of victims and a decades-long history of manipulation and deception," said Ben Wogsland, the spokesman.

Fantasy logs

Duvall's case, heard by the appeals panel last April, revealed a man still struggling to control his deviant sexual thoughts. These were detailed in hundreds of pages of "fantasy logs," maintained as part of his treatment at the MSOP, where Duvall described violent fantasies involving past victims and female body parts. Dr. James Alsdurf, a forensic psychologist appointed by the state Supreme Court appeals panel, testified that the logs showed that Duvall was still "hypersexual" and "obsessed with sex," and was not ready for release.

In addition, Duvall failed to pass most in a series of lie detector tests. The judges' panel, however, appeared to be persuaded by members of Duvall's treatment team at the MSOP, who testified that he had shown significant progress in treatment. Duvall had gone on more than 100 supervised outings, volunteered at a thrift shop three times a week, and regularly attended a men's support group in Minneapolis — all without incident, they said.

At the same time, the judges acknowledged that Duvall "may never be free from deviant sexual thoughts" and the "management of these thoughts" should be the focus of his treatment.

Warren Maas, an attorney who represented Duvall when he was committed in 1991, said the panel's recommendation is an opportunity for the state to prove it can provide effective treatment in the community. "The MSOP should be cheering this decision," he said. "[Duvall] has done everything this program has asked him to do, and now he has the opportunity to demonstrate that he has really changed his behavior."

Under legal pressure in the last two years, the MSOP and the state appeals panel have begun moving an unprecedented number of offenders toward release. To date, 23 offenders have been conditionally discharged from the program, most of them in the last few years. Of those, nine are now living in community facilities under strict surveillance. In addition, 89 are living in Community Preparation Services, a transitional unit outside the secure perimeter of the St. Peter campus, while another 26 were waiting for beds to open there.

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