ST. PAUL — A three-judge panel has cleared a serial rapist, whose case once triggered a political firestorm, for conditional release from the Minnesota Sex Offender Program, but the state Department of Human Services said Tuesday that it would appeal.

Thomas R. Duvall, 62, has spent the past 30 years locked up for the violent rapes of teenage girls in the 1970s and 1980s. In 1987, Duvall bound a Brooklyn Park girl with an electrical cord and raped her repeatedly over several hours while hitting her with a hammer.

The judicial panel on Monday approved Duvall’s provisional discharge, saying his progress in treatment outweighs his “fearful diagnosis” as a sexual sadist, according to a press release.

At a hearing last April, therapists and others program staffers depicted Duvall as a reformed man who was contrite about his violent history and ready for a return to the community.

But Human Services Commissioner Emily Piper said she’ll try to block his release.

“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 statement. “I disagree with the court’s decision to the contrary and will appeal this decision.”

Duvall dropped a previous attempt at partial freedom four years ago. While MSOP staffers had recommended his release, Attorney General Lori Swanson objected. After Republican lawmakers also objected, Democratic Gov. Mark Dayton ordered his administration to oppose further releases until the program could be changed.

Under his proposed discharge plan, Duvall will live under intensive 24-hour supervision with GPS monitoring in a facility operated by Zumbro House, which provides community housing to sex offenders, and will not be allowed to leave unless accompanied by staff.

The U.S. Supreme Court last October declined to hear a major challenge to the constitutionality of Minnesota’s civil commitment program for sex offenders. While a federal judge declared the program unconstitutional because few people in it had ever won release, the 8th Circuit Court of Appeals overruled him.

The program currently holds 726 people in secure treatment facilities in Moose Lake and St. Peter. The department said nine clients are living in supervised community facilities, while 12 others who’ve been granted provisional discharges, including Duvall, are still awaiting placements.