Cal. Penal Code § 939.1

The grand jury acting through its foreman and the attorney general or the district attorney may make a joint written request for public sessions of the grand jury. The request shall be filed with the superior court. If the court, or the judge thereof, finds that the subject matter of the investigation affects the general public welfare, involving the alleged corruption, misfeasance, or malfeasance in office or dereliction of duty of public officials or employees or of any person allegedly acting in conjunction or conspiracy with such officials or employees in such alleged acts, the court or judge may make an order directing the grand jury to conduct its investigation in a session or sessions open to the public. The order shall state the finding of the court. The grand jury shall comply with the order. The conduct of such investigation and the examination of witnesses shall be by the members of the grand jury and the district attorney. The deliberation of the grand jury and its voting upon such investigation shall be in private session. The grand jury may find indictments based wholly or partially upon the evidence introduced at such public session.