在美国，成立不成立grand juries是检察官决定。grand juries 只听检察官一方的辩论。

“Grand juries are built to be a tool of prosecutors. They don’t hear from both sides in a case, like a trial jury would. They hear only from the prosecutor, who decides what evidence and testimony is presented.”

https://www.washingtonpost.com/posteverything/wp/2015/12/29/in-tamir-rices-case-the-grand-jury-process-was-turned-upside-down/