Due to the uniqueness of the death penalty, the Supreme Court requires heightened reliability in the decisions made by the jury and judge during the course of a capital trial. See, e.g., Zant v. Stephens, 462 U.S. 862, 884 (1983). In Woodson v. North Carolina, 428 U.S. 280 (1976), the Court explained why the Constitution requires an individualized sentencing determination in a capital case even though there is no parallel requirement in non-capital cases.
This conclusion rests squarely on the predicate that the penalty of death is qualitatively different from a sentence of imprisonment, however long. Death, in its finality, differs more from life imprisonment than a 100-year prison term differs from one of only a year or two. Because of that qualitative difference, there is a corresponding difference in the need for reliability in the determination that death is the appropriate punishment in a specific case.
428 U.S. at 305. In short, death is different. Thompson v. Oklahoma, 487 U.S. 815, 856 (1988) ("Under the Eighth Amendment, the death penalty has been treated differently from all other punishments").
The heightened need for reliability in capital cases has been relied upon by the Court in a variety of contexts as an important rationale for its decisions.
Woodson v. North Carolina, 428 U.S. at 304-05 (invalidating mandatory capital sentencing statute);
Gardner v. Florida, 430 U.S. 349 (1977) (requiring disclosure to defendant of all information contained in confidential presentence investigation report in sufficient time to allow defendant a meaningful opportunity for response);
Lockett v. Ohio, 438 U.S. 586, 603-05 (1978) (requiring consideration of all relevant mitigating evidence to avoid "the risk that the death penalty will be imposed in spite of factors which may call for a less severe penalty");
Green v. Georgia, 442 U.S. 95 (1979) (forbidding the exclusion of relevant mitigating evidence due to the state's hearsay rule);
Beck v. Alabama, 447 U.S. 625 (1980) (requiring instruction on lesser included offenses supported by the evidence in the guilt phase of a capital trial);
Bullington v. Missouri, 451 U.S. 430 (1981) (holding that double jeopardy bars death sentence on retrial after defendant sentenced to life at first trial);
Estelle v. Smith, 451 U.S. 454 (1981) (recognizing that Fifth Amendment right against self-incrimination and Sixth Amendment right to counsel are applicable to penalty phase of capital trial);
Caldwell v. Mississippi, 472 U.S. 320 (1985) (forbidding prosecutorial argument which, by assuring the jury that any error it made could be corrected on appeal, had the effect of diminishing the jury's sense of responsibility for its sentencing decision);
Turner v. Murray, 476 U.S. 28 (1986) (requiring the states to permit voir dire about racial prejudice in interracial crimes);
Lankford v. Idaho, 500 U.S. 110 (1991) (recognizing that capital defendant is entitled to fair notice of issue to be resolved at trial);
1 But see Barefoot v. Estelle, 463 U.S. 880 (1983) (allowing the admission of psychiatric testimony regarding future dangerousness even though such testimony is inherently unreliable); Pulley v. Harris, 465 U.S. 37 (1984) (refusing to require proportionality review on appeal of death sentence); Strickland v. Washington, 466 U.S. 668 (1984) (refusing to require higher standards for counsel's performance in death cases); Spaziano v. Florida, 468 U.S. 447 (1984) (permitting judge override of jury sentencing determination); Baldwin v. Alabama, 472 U.S. 372 (1985) (refusing to condemn a sentencing scheme in which the jury was required to recommend death upon conviction of certain aggravated crimes but the judge thereafter sentenced on the basis of her own "independent" consideration of the evidence); Lockhart v. McCree, 476 U.S. 162 (1986) (approval of present practice of "death-qualification" of jurors despite substantial evidence that the resulting jury is biased in favor of the prosecution); Darden v. Wainwright, 477 U.S. 168 (1986) (approving conviction and sentence despite prosecutor's concededly improper closing argument, which reflected an emotional and personal reaction to the case and contained references to the defendant as an "animal" who should have been kept on a leash); Payne v. Tennessee, 501 U.S. 808 (1991) (State may admit victim-impact evidence at sentencing phase); Harris v. Alabama, 513 U.S. 504 (1995) (Eighth Amendment does not require sentencing judge to ascribe any particular weight to the verdict of an advisory jury).