A judge dealt a setback March 2 to Governor Napolitano’s administration, ruling that a special prosecutor can use a grand jury to investigate a 15-day prison standoff.

Subject to oversight by the courts, grand juries can go beyond their traditional role of producing criminal indictments, said Judge Eddward P. Ballinger Jr. of Maricopa County Superior Court.

However, Judge Ballinger also ruled that special prosecutor A. Melvin McDonald Jr. must seek further court permission to expand the grand jury’s inquiry into an “administrative investigation” and to release information to the public.

Judge Ballinger, the presiding criminal judge, also ordered that Mr. McDonald not appear before the grand jury until his appointment by County Attorney Rick Romley is approved by the County Board of Supervisors. The supervisors formalized the appointment in a meeting March 3, naming Mr. McDonald as a special deputy county attorney.

Grand juries meet behind closed doors and their proceedings are secret until criminal charges result. Judge Ballinger’s ruling came on a motion filed by the Attorney General’s Office on behalf of the Corrections Department.

The state’s motion sought to dismiss or limit the scope of a grand jury called for Mr. McDonald’s investigation into the circumstances surrounding the standoff and hostage situation at the Lewis state prison in Buckeye.

Attorney General’s Office spokeswoman Andrea Esquer said the office would confer with the Corrections Department before deciding whether to appeal Judge Ballinger’s ruling.

A state lawyer had argued in court March 1 that a grand jury can only be used for criminal matters, while Mr. McDonald argued that state law gives grand juries broad discretion.

The hostage-taking at the state prison in Buckeye led to the standoff that ended Feb. 1 when two inmates surrendered and released their final hostage, a female corrections officer.

Mr. Romley deputized Mr. McDonald, a former U.S. attorney and ex-judge, to conduct an investigation at the request of the Republican legislative leaders.

Mr. McDonald has said he wants the grand jury to issue a public report on the standoff. He also has said a grand jury is a valuable fact-finding tool because it can compel testimony and take it secretly.

Ms. Napolitano’s commission issued its own preliminary report on March 4. —

Associated Press writer Jacques Billeaud contributed to this report.