By Bob Egelko

A federal appeals court upheld a voter-approved state law Thursday that allows sex offenders who have completed their prison sentences to be locked up for life if a jury determines they are mentally disturbed and dangerous.

A Sacramento County man who has been held in state hospitals since the scheduled end of his prison term in 1997 challenged the ballot measure as discriminatory, noting that other offenders whose confinement is prolonged because of mental disorders are entitled to a jury trial every year to determine whether they should be released.

But the Ninth U.S. Circuit Court of Appeals said the state is entitled to treat sex offenders more harshly, even after they have served their sentences.

"A state rationally may decide that sexually violent crime is qualitatively more dangerous than other kinds of violent crime," said Judge Susan Graber in the 3-0 decision.

The ruling came a day after a federal judge struck down a law in Minnesota that extends the confinement of sex offenders after their prison sentences. The judge said the program virtually guarantees a lifelong hospital stay, even for those who have been treated successfully. The conflict in lower-court rulings could bring the issue to the U.S. Supreme Court.

California's "sexually violent predator" law allows the state to extend the confinement of a violent sex criminal if a jury finds, at the end of the inmate's sentence, that he or she suffers from a mental disorder and is likely to commit another violent sex crime if released.

The law originally entitled inmates to a new jury trial on the issue every two years. But Proposition 83 in 2006, also known as Jessica's Law, said an inmate could be confined indefinitely, potentially for life. The inmate can still ask for another jury trial at any time, but would then have to convince jurors that he or she is no longer dangerous.

The court case involved Timothy Seeboth, who was convicted of nine sex crimes against children over a period of more than 30 years and was scheduled to be released from prison in 1997. State mental health officials then classified him as a sexually violent predator, and juries confirmed that diagnosis every two years until after voters approved Prop. 83. Another jury then approved his indefinite confinement.

Seeboth's lawyer, Michael Bigelow, said after Thursday's decision that he would ask the full appeals court for a rehearing. He said Prop. 83 was sold to the voters based on a purported study showing sex offenders were more likely than other convicts to commit crimes after release.

That study "doesn't exist," Bigelow said. "There's no medical or scientific evidence that establishes sexual offenders have a higher (recidivism) rate than non-sexual offenders."

(c)2015 the San Francisco Chronicle