Justice Rehnquist would have affirmed because, in his view, Ake had not made a sufficient factual showing that his sanity at the time of the offenses was genuinely in dispute. A diagnosis of mental illness roughly six months later did not establish a reasonable doubt about whether Ake knew right from wrong during the crimes, especially because the examining psychiatrists would not offer that conclusion.
He faulted the majority for not explaining how Ake met its own threshold requirement. Under Oklahoma law, Ake bore the initial burden of producing evidence that raised a reasonable doubt as to sanity, and the State had introduced no evidence on the issue. Rehnquist concluded that Ake simply failed to meet that state-law burden rather than suffered a federal due-process violation.
Rehnquist also argued that due process does not generally require a State to finance an indigent defendant's preferred development of a state-created insanity defense. At most, he would recognize a right in capital cases where the State bears the burden on sanity or future dangerousness and makes significant use of psychiatric evidence.
He regarded the majority's sentencing discussion as unnecessary once it ordered a new guilt-phase trial. Moreover, he noted that the future-dangerousness testimony came from psychiatrists called by Ake, rather than from prosecution experts, so he saw no basis for requiring the State to provide further psychiatric assistance.
Even if some entitlement existed, Rehnquist would limit it to an independent psychiatric evaluation. He rejected a constitutional right to a defense-oriented psychiatric consultant who would assist in evaluation, preparation, and presentation, reasoning that the relevant need was for an independent competent opinion, not an expert advocate.