The standard developed over case law IMO. It only requires a vote of more than half of the grand jurors voting once a quorum is reached. Reasonable cause is another term used in this process...it is merely a statement, or true bill, there is reason to bring the matter to trial. In essence the prosecutor shows a violation has occurred and he puts the proposed defendant present during its occurance.
With no defense testimony taken or defense counsel present, it is kind of a rubber stamp most times.
Lastly the grand jury is used rather than a preliminary hearing to limit the disclosure of evidence a prosecutor has amassed. Recent case law has developed that there is NO requirement to report exculpatory evidence making the grand jury more of a rubber stamp IMO.
I don’t know either, but my question would be, why wouldn’t indictment by a GJ not be considered a “seizure” under the 4th Amendment requiring “reasonableness” (probable cause)?