John Paul Stevens

“ Respondent instead claims, as did the defendant in Mallett, that an unrelated error must bar the State from relying upon his concededly valid conviction, and predicates this claim solely on a restriction upon the State's access to appellate-or, more precisely in this case, postconviction-remedies. [4] Unlike the defendants in Thompson and Kring, Youngblood wishes to have a new trial according to the same procedures, regulated by the same laws, open to the same evidence, and capped by the same sentencing limitations that resulted in his conviction and his life sentence. ”

“ In the case before us the Constitution of Missouri so changes the rule of evidence, that what was conclusive evidence of innocence of the higher grade of murder when the crime was committed, namely, a judicial conviction for a lower grade of homicide, is not received as evidence at all, or, if received, is given no weight in behalf of the offender. ”

“ It also changes the punishment, for, whereas the law as it stood when the homicide was committed was that, when convicted of murder in the second degree, he could never be tried or punished by death for murder in the first degree, the new law enacts that he may be so punished, notwithstanding the former conviction. ”

“ Of course, a statute is not of that class unless it materially impairs the right of the accused to have the question of his guilt determined according to the law as it was when the offence was committed. ”