Sentence:  Rumors of the offer Tom Horn had made at the Stockgrowers' Association meeting had leaked out by then , and as a <WSD>grand</WSD> jury investigation of the murder got underway , the prosecuting attorney , a Colonel Baird , ordered that the tall stock detective be summoned for questioning . 
Meaning of the word marked with <WSD> tags:  a jury to inquire into accusations of crime and to evaluate the grounds for indictments