Respondent was sentenced to 15 years to life for the 1980 murder of his wife and became eligible for parole in 1990. As required by California law, the Board of Prison Terms (Board) held a hearing in 1989, at which time it found respondent unsuitable for parole for numerous reasons, including the fact that he had committed his crime while on parole for an earlier murder. Respondent would have been entitled to subsequent suitability hearings annually under the law in place when he murdered his wife. The law was amended in 1981, however, to allow the Board to defer subsequent hearings for up to three years for a prisoner convicted of more than one offense involving the taking of a life, if the Board finds that it is not reasonable to expect that parole would be granted at a hearing during the intervening years and states the bases for the finding. Pursuant to this amendment, the Board scheduled respondents next hearing for 1992. He then filed a federal habeas corpus petition, asserting that as applied to him, the 1981 amendment constituted an ex post facto law barred by the United States Constitution. The District Court denied the petition, but the Court of Appeals reversed, holding that the retrospective law made a parole hearing less accessible to respondent and thus effectively increased his sentence in violation of the Ex Post Facto Clause.

Held:

The amendments application to prisoners who committed their crimes before it was enacted does not violate the Ex Post Facto Clause. Pp. 4-14.

(a) The amendment did not increase the "punishment" attached to respondents crime. It left untouched his indeterminate sentence and the substantive formula for securing any reductions to the Page II sentencing range. By introducing the possibility that the Board would not have to hold another parole hearing in the year or two after the initial hearing, the amendment simply alters the method to be followed in fixing a parole release date under identical substantive standards. Lindsey v. Washington, 301 U.S. 397, Miller v. Florida, 482 U.S. 423, and Weaver v. Graham, 450 U.S. 24, distinguished. Pp. 4-8.

(b) Under respondents expansive view, the Clause would forbid any legislative change that has any conceivable risk of affecting a prisoners punishment. In contrast, this Court has long held that the question of what legislative adjustments are of sufficient moment to transgress the constitutional prohibition must be a matter of degree, and has declined to articulate a single "formula" for making this determination. There is no need to do so here, either, since the amendment creates only the most speculative and attenuated possibility of increasing the measure of punishment for covered crimes, and such conjectural effects are insufficient under any threshold that might be established under the Clause. The amendment applies only to those who have taken more than one life, a class of prisoners for whom the likelihood of release on parole is quite remote. In addition, it affects the timing only of subsequent hearings, and does so only when the Board makes specific findings in the first hearing. Moreover, the Board has the authority to tailor the frequency of subsequent hearings. Respondent offers no support for his speculation that prisoners might experience an unanticipated change that is sufficiently monumental to alter their suitability for parole, or that such prisoners might be precluded from receiving a subsequent expedited hearing. Nor is there a reason to think that postponing an expedited hearing would extend any prisoners actual confinement period. Since a parole release date often comes at least several years after a suitability finding, the Board could consider when a prisoner became "suitable" for parole in setting the actual release date. Pp. 8-14.

THOMAS, J.,