MINNEAPOLIS — Four experts appointed to evaluate a Minnesota program that confines some sex offenders to high-security facilities even after they have served prison sentences said they need more time to complete their work.

The request, made last week, came just two days after U.S. District Judge Donovan Frank said he wanted to expedite the case, which alleges the Minnesota Sex Offender Program is unconstitutional, and schedule it for trial in 2014. The experts, who include psychologists and officials from other states with similar programs, wrote in their Aug. 13 letter that they were too optimistic when they told the court they could have a comprehensive report completed by the end of August. They asked for an extension until mid- or late-November.

“We are aware that the stakes are high and that the Court and parties wish to expedite the process; however, the complexity of the issues at hand and our respective responsibilities and schedules … interfere with our ability to complete a detailed report before the end of August in the professional manner required,” the experts wrote.

Frank wrote that the court “will be discussing this and its implications” at a status conference this Thursday.

The experts are reviewing the Minnesota Sex Offender Program as part of a class-action lawsuit filed in 2011 by its residents, who allege it is unconstitutional because it keeps them locked up indefinitely without providing adequate treatment. Nearly 700 people deemed sexually dangerous or sexual psychopaths have been committed to high-security facilities in Moose Lake or St. Peter after their prison terms were completed. Only one resident has been successfully released, with provisions, since 1994.

In their letter to Frank, the experts said they have reviewed the vast majority of residents in three specialized programs, as well as most residents with severe and persistent mental illness. The experts have also met with program leaders and interviewed staff and residents at both facilities. They still plan to review a random sample of conventional program residents.

They said they would like to complete their review followed by issuing a report that will address the extent to which the program’s treatment meets professional standards, and whether its policies satisfy a balance between safety and therapy. If necessary, they plan to recommend changes.

The experts were also asked to examine how other commitment programs have reintegrated sex offenders into the community and how other states are treating and managing lower-functioning committed sex offenders in community settings, their letter said.

They said they need more time to examine the issues in enough detail, so their findings will be meaningful to the court.