Okla. Stat. tit. 22, § 22-335: Evidence for the accused - Procuring additional evidence

The grand jurors, upon request of the accused, shall, and on

their own motion may, hear the evidence for the accused. It is

their duty to weigh all the evidence submitted to them and when they

have reason to believe that there is other evidence, they may order

such evidence to be produced, and for that purpose the State's

Attorney shall cause process to issue for the witnesses.