Prison officials are refusing say to how or where the state acquired 12 grams of sodium thiopental, with a 2014 expiration date.
In September, a judge put the execution of rapist-murderer Albert Brown on hold because California's stockpile of the drug had expired and the company that makes it ran out.
Human rights advocates contend the state must have gotten the drug from a foreign producer and have voiced concern over the safety of the product.
