“ The right to a competent psychiatrist necessarily includes the right to have the State provide the psychiatrist with the tools he requires to conduct an adequate examination and evaluation of the defendant. To hold otherwise is analogous to requiring the State to provide an indigent defendant with an attorney, but not requiring it to pay for the attorney's legal research expenses.
This is not to say that an indigent defendant is entitled to every scientific procedure that has only a remote possibility of bolstering his defense. ”

“ Masland's opinion that testing would be superfluous-an opinion not shared by any of the other doctors-does not justify its denial of access to testing. Ake requires the appointment of a psychiatrist who will assist in the preparation of the defense, not one who will merely give an independent assessment to the judge or jury. 470 U.S., at 83, 105 S.Ct., at 1096. Although a judge or jury may choose to believe the State's experts rather than the defendant's at trial, a court may not permit the State's experts to determine what resources the defendant's experts may use. ”

“ But when a defendant demonstrates that his sanity will be a significant issue at trial, and his psychiatrist makes a plausible showing that certain testing is necessary for him to perform his Ake function, that testing must be considered one of "the raw materials integral to the building of an effective defense" that the State must provide. 470 U.S., at 77, 105 S.Ct., at 1093.
Petitioner undoubtedly satisfied the threshold requirements. First, his sanity was a significant factor in his defense. ”