No grand jury shall be summoned to attend at the superior court of any county except upon an order signed by a majority of the judges thereof. A grand jury shall be summoned by the court, where the public interest so demands, whenever in its opinion there is sufficient evidence of criminal activity or corruption within the county or whenever so requested by a public attorney, corporation counsel or city attorney upon showing of good cause.
[ 1971 ex.s. c 67 § 3.]