Hearsay evidence would be good enough for a grand jury to indict Obama before moving on with the investigation.
"The RULES OF EVIDENCE prohibit the introduction of most HEARSAY evidence in a criminal trial. (Hearsay is evidence given by a person concerning what someone else said outside of court.) However, when Frank Costello, alias Francisco Castaglia, a notorious ORGANIZED CRIME figure of the 1940s and 1950s, argued that his conviction for federal income TAX EVASION should be overturned because the grand jury that indicted him heard only hearsay evidence, the Supreme Court rejected his claim (Costello v. United States, 350 U.S. 359, 76 S. Ct. 406, 100 L. Ed. 397 [1956])."
http://law.jrank.org/pages/7196/Grand-Jury-Hearsay-Evidence-Admissible-before-Grand-Jury.html
IMO if the normal rules of law were being applied to this case—or to the discovery of public documents in Hawaii and elsewhere—then this case would already be proceeding in the courts.
But they aren’t and it isn’t. No court wants to touch this hot potato and judges and appeals courts are very good at avoiding what they don’t want to handle.