A specially-empaneled statewide grand jury convened pursuant to this chapter shall sit for a period not to exceed 18 months. The superior court justice presiding over the statewide grand jury may extend that period if, in accordance with section 41 of chapter 234A and section 1A of chapter 277, public necessity requires further time by the statewide grand jury to complete an ongoing investigation.
Mass. Gen. Laws ch. 277B, § 5