You don't understand how it works.
An investigation is conducted by the grand jury.
The grand jury has broad investigative powers. Ariz. Rev. Stat. § 21-408. A. The county attorney or other prosecuting officer shall attend the grand jurors when requested by them, and may do so although not requested for the purpose of examining witnesses, in their presence, or of giving the grand jurors legal advice regarding any matter cognizable by them. He shall also, when requested by them, draft indictments and cause process to issue for the attendance of witnesses and other evidence. (emphasis added)
If you are going after the president of the united states then everything...
The issue is a private individual seeking ballot access. Identity documents publicly displayed by said individual appear to be fake. An investigation by a grand jury is called for.
"Arizona Revised Statutes - Title 21 Juries
Section 21-407 Duties of grand jurors
21-407. Duties of grand jurors
A. The grand jurors shall inquire into every offense which may be tried within the county which is presented to them by the county attorney or other prosecuting officer at the request of the county attorney, or by the attorney general as a special prosecutor appointed by the presiding judge of the superior court for the purpose of proceedings under section 21-408, subsection B, or section 38-344, and shall have access to all jails, public institutions, and public records."
No judge or DA is going to use Sheriff Joe's posse investigation as probable cause to go to a grand jury.
The Maricopa County County Attorney has his own investigators. I would imagine he could conduct his own investigation if he wanted to - I doubt he will.
There is no credible evidence that the documents are fake. The "investigation" was tainted - therefore the results are tainted too.