The state Supreme Court upheld a law Thursday that allows a Death Row inmate from Contra Costa County, and others sentenced to death or life without parole, to seek post-trial evidence from prosecutors that might assist their appeals.

Prosecutors argued that a 2002 law on post-trial rights for some convicted murderers violated an initiative passed 12 years earlier that limited defendants' rights to obtain evidence. The court disagreed unanimously.

The case involves Michael Pearson of Richmond, who was sentenced to death for murdering his supervisor and her assistant in April 1995 after he was fired as a receptionist at the city Housing Authority.

Pearson, 52, is awaiting a state Supreme Court hearing on an appeal of his conviction and sentence, based on alleged errors at his trial. Thursday's ruling involved a separate proceeding, habeas corpus, in which a prisoner challenges the verdict based on issues outside the trial record, such as incompetent legal representation, juror misconduct or newly discovered evidence.

A prisoner usually must persuade a court that such claims have some factual support before demanding evidence from prosecution files. The 2002 law, which applied only to inmates sentenced to death or life without parole, allowed them to obtain prosecution evidence while preparing to file their habeas corpus claims, and to use that evidence to try to persuade a court to hear the claims.

Pearson's prosecutors argued that the law violated Proposition 115, a 1990 ballot measure that revised California's trial procedures to limit defendants' rights. It included rules for the pretrial exchange of evidence, known as discovery, and prohibited any other discovery orders in criminal cases unless authorized by a two-thirds legislative majority.

The state's high court said Thursday that habeas corpus, a post-trial proceeding, is not part of a criminal case and therefore is not subject to Prop. 115's restrictions. That means the 2002 law is valid even though it was passed by only a majority of the Legislature and not a two-thirds majority, said Justice Ming Chin.

Pearson's lawyer, David Lane, said the ruling would reduce delay in habeas corpus proceedings and increase their accuracy by making more evidence available. He declined to discuss the evidence he sought from Pearson's prosecutors. A prosecution lawyer was unavailable for comment.