Marin County Superior Court Judge Faye D'Opal found the state's failed to consider a single-injection protocol as a replacement for the three-drug cocktail that a federal court had found unconstitutional, the Los Angeles Times reported.
California has not carried out an execution since that federal court ruling in February 2006.
The California Department of Corrections and Rehabilitation is likely to appeal D'Opal's ruling, the newspaper said.
Natasha Minsker -- a lawyer with the American Civil Liberties Union of Northern California lawyer who is also campaign manager for a drive to get the state's death penalty repealed -- told the Times the state should replace execution with sentences of life in prison with no possibility of parole.
"Any attempt to devise new lethal-injection rules will take an enormous amount of public employee time and cost hundreds of millions of dollars," Minsker said.
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