A convicted serial rapist at the center of a highly charged sex offender case has destroyed sexually explicit journals that could have been key evidence for those who oppose his release from state custody.

At a court hearing Monday, an attorney for Thomas Duvall, 58, acknowledged that his client had destroyed so-called "fantasy logs" that he kept while undergoing therapy in the Minnesota Sex Offender Program (MSOP).

Minnesota Attorney General Lori Swanson and a court-appointed psychologist have sought copies of Duvall's logs, which reportedly contain his thoughts and fantasies of sexually violent encounters. Swanson, who intervened last year to oppose Duvall's release, filed a court motion in March accusing him of spoiling relevant evidence.

"In a case as important as this, we should see all the available data," said Dr. James Alsdurf, a forensic psychologist appointed by a state appeals panel to review Duvall's condition.

The destruction of Duvall's fantasy logs marks another strange twist in a case that has already made a mark on this year's campaign for governor.

Late last year, GOP lawmakers blasted Gov. Mark Dayton for failing to oppose the MSOP's plan for a supervised discharge for Duvall, who committed a string of assaults on teenage girls in the 1970s and 1980s. In one particularly horrific incident in 1987, Duvall tied up his victim with an electrical cord and then raped her repeatedly while hitting her with a hammer.

An evidentiary hearing on Duvall's proposed discharge, requested by Swanson and scheduled for this week, has been postponed to mid-September so that psychologists can review his treatment history. The delay could put officials from the Dayton administration in the awkward position of defending the discharge of a violent serial rapist just before the November election.

The debate over Duvall's future has already claimed one professional casualty. In February, a Hennepin County prosecutor, George Widseth, who supported Duvall's provisional discharge, was removed from the case and took a medical leave after he made incendiary comments directed at the state solicitor general, who opposes Duvall's release.

Since Widseth was removed, the Hennepin County attorney's office has changed its position on the case, now saying it will withhold judgment until the experts have completed their analysis.

"It's Kabuki theater," said William Lubov, a Twin Cities attorney who represents Duvall, referring to the Japanese theater genre with illusions and highly stylized characters. "Everyone is trying to get on a soapbox on this, and no one wants a quick resolution because that means fingers get pointed." Lubov declined to comment on the status of the fantasy logs, except to confirm they were destroyed.

The logs kept by Duvall were among more than 6,000 pages of documents, including Duvall's treatment records and psychological assessments, that experts had planned to review before making their final recommendations on his proposed discharge. According to court documents, the logs contain "offense-related sexual thoughts and fantasies related to juveniles and sexual violence."

The fantasy logs were considered so troubling that Dayton even mentioned them in an e-mail last September to Human Services Commissioner Lucinda Jesson, whose department oversees the MSOP. In the e-mail, Dayton asked Jesson, "How do you respond to the 2012 fantasy logs? Also to the # & severity of his crimes? Mark."

Swanson's office sought the logs because Dr. David Thornton, a psychologist appointed by DHS, reviewed them in supporting Duvall's petition for provisional discharge, according to court documents. In March, a panel of judges ordered Duvall to "produce any and all records in his possession," including the logs.

It is unclear if copies of the logs were ever created and could be submitted as evidence later.

The push to consider the fantasy logs as evidence, however, is considered controversial, in part because sex offenders are often required to maintain personal journals while undergoing therapy. If the journals can later be used as evidence against them, sex offenders might not be candid in treatment, advocates have argued.

"It's an absolute Catch-22," said Warren Maas, executive director of Project Pathfinder, which treats sex offenders and helps them make the transition into the community. "If you don't [keep a journal], then you don't get released. If you do do it, then the attorney general or someone else will bring it up at a hearing opposing your release."

Maas added, "Unfortunately, I don't think the legal system understands clinical thinking, so these fantasy logs are misinterpreted. Fantasies don't necessarily lead to violent behavior."

Chris Serres • 612-673-4308

Twitter: @chrisserres