A federal judge in Minnesota has ruled that Congress exceeded its authority when it allowed federal officials to commit mentally disordered sex offenders to treatment centers at the time of their release from prison.

In a decision filed this week, U.S. District Judge Paul Magnuson dismissed a petition by Rachel Paulose, former U.S. attorney for Minnesota, to prolong the confinement of Roger Dean Tom, who was due to be released from the Federal Medical Center in Rochester.

Paulose blocked Tom's release by petitioning the court in October 2006 to have him declared a sexually dangerous person under the Adam Walsh Child Protection and Safety Act, passed just three months earlier.

While the U.S. Supreme Court has approved states' use of civil commitments for sex offenders -- 19 states, including Minnesota, have such laws -- Magnuson ruled that the Constitution prohibits the type of broad cross-jurisdictional authority that the law gave federal prosecutors for such commitments.

According to case documents, the ruling was the fifth nationally by district judges on the law -- three ruled it valid, and two found it unconstitutional. An appeals court has yet to decide the issue.

Tom pleaded guilty in Utah in 1997 to a count of aggravated sexual abuse and was sentenced to 10 years in prison and five on supervised release. He was finishing prison at the Rochester facility when prosecutors sought his commitment.

David Anderson, spokesman for the U.S. attorney's office in Minneapolis, said prosecutors declined to speak about the case or say whether they would appeal. Tom remains an inmate at the Rochester facility, an official there said. Tom's attorney, Caroline Durham, could not be reached.

Magnuson rejected arguments that the law was justified by the Commerce Clause, which permits laws necessary for interstate commerce, and the Necessary and Proper Clause, which permits laws needed for government to operate on a national scale.

In contrast to federal drug trafficking laws and others related to national commerce, Magnuson wrote, the commitment law "is unrelated to economics but rather aims to regulate and prevent noneconomic criminal conduct that traditionally has been the province of the states."

While the Necessary and Proper Clause clearly allows Congress to devise laws to confine people until prosecuted, Magnuson wrote, that authority doesn't extend to holding them beyond their sentences.

"The government has identified no clause in the Constitution that authorizes Congress to prevent future criminal conduct," he wrote.

Magnuson said the government's strongest argument -- that courts have found the Necessary and Proper Clause justified forcing inmates to give DNA for a national registry -- wouldn't fly in this case. Retaining a released inmate's DNA sample "is fundamentally different than retaining custody of the inmate," he wrote.

Larry Oakes • 1-218-727-7344