Anyone involved in a capital litigation must have a firm grasp of the Lockett doctrine. In Lockett v. Ohio, 438 U.S. 586 (1978), the Court established the bedrock Eighth Amendment principle emanates from the "the fundamental respect for humanity underlying the Eighth Amendment, [which mandates the ]. . consideration of the character and record of the individual offender and the circumstances of the particular offense as a constitutionally indispensable part of the process of inflicting the penalty of death." Id. at 304; see also Roberts (Harry) v. Louisiana, 431 U.S. 633 (1977); Roberts (Stanislaus) v. Louisiana, 428 U.S. 325 (1976).1 Only through a process which requires the sentencer to "consider in fixing the ultimate punishment of death the possibility of compassionate or mitigating factors stemming from the diverse frailties of humankind," Woodson v. North Carolina, 428 U.S. 280, 304 (1976), can capital defendants be treated "as uniquely individual human beings." Id. The Lockett principle "is the product of a considerable history reflecting, the law's effort to develop a system of capital punishment at once consistent and principled but also humane and sensible to the uniqueness of the individual. California v. Brown, 479 U.S. 537, 562 (1987) (Blackman, J. dissenting). Or, in Justice O'Connor's terms, "[u]nderlying Lockett and Eddings is the principle that punishment should be directly related to the personal culpability of the criminal defendant." Penry v. Lynaugh, 492 U.S. 302, 319 (1989), overruled in part on other grounds by Atkins v. Virginia, 536 U.S. 304 (2002).
Because of the need for individualized treatment, the states have been required to permit the sentencer to consider, and in appropriate cases base a decision to impose a life sentence upon any relevant mitigating factor, not simply the mitigating factors specified in a statute. Hitchcock v. Dugger, 481 U.S. 393 (1987). As explained in Eddings v. Oklahoma, 455 U.S.104 (1982),
Lockett followed from the earlier decisions of the Court and from the Court's insistence that capital punishment be imposed fairly, and with reasonable consistency, or not at all. . . . By holding that the sentencer in capital cases must be permitted to consider any relevant mitigating factor, the rule in Lockett recognizes that a consistency produced by ignoring individual differences is a false consistency.
455 U.S. at 112.
It is important to note that the definition of "mitigating" is extremely broad. In Lockett, the Court defined a mitigating circumstance as "any aspect of a defendant's character or record and any of the circumstances of the offense that the defendant proffers as a basis for a sentence less than death." 438 U.S. at 604. While this explanation seems to allow the defendant the freedom to define what is "mitigating," the Court has since given a more objective cast to this explanation. In Skipper v. South Carolina, 476 U.S. 1 (1986), the Court held that evidence of the defendant's good behavior during his pretrial incarceration was "'mitigating' in the sense that [it] might serve 'as a basis for a sentence less than death.'" 476 U.S. at 7 (quoting Lockett v. Ohio, 438 U.S. at 604).2 Thus, any evidence which "might" serve to reduce the urge to punish harshly must be deemed mitigating. See also McKoy v. North Carolina, 494 U.S. 433, 440 (1990) (quoting State v. McKoy, 323 N. C. 1, 55-56, 372 S. E. 2d, 12, 45 (1988) (opinion of Exum, C. J.) ("`Relevant mitigating evidence is evidence which tends logically to prove or disprove some fact or circumstance which a fact-finder could reasonably deem to have mitigating value.'"); Tennard v. Dretke, 542 U.S. 274 (2004) (a defendant need not show a “uniquely severe permanent handicap” and that the capital offense was attributable to such handicap to establish relevant mitigation); but see Oregon v. Guzek, 546 U.S. 517 (2006) (at penalty phase retrial, Eighth Amendment does not provide defendant with the right to present new but previously available evidence showing he was not present at the scene of the crime).
A corollary Lockett principle is that sentencer must be permitted to give "independent mitigating weight," Lockett v. Ohio, 438 U.S. at 605, to all evidence proffered in mitigation. See also Abdul-Kabir v. Quarterman, 550 U.S. 233, 246 (2007) (“[O]ur cases had firmly established that sentencing juries must be able to give meaningful consideration and effect to all mitigating evidence that might provide a basis for refusing to impose the death penalty on a particular individual, notwithstanding the severity of his crime or his potential to commit similar offenses in the future.”) Thus there cannot be any distinction between statutory and nonstatutory mitigating circumstances. See Hitchcock v. Dugger, 481 U.S. 393 (1987).3 Additionally, the jury instructions must be sufficient to provide the jury "with a vehicle for expressing its reasoned moral response to that evidence in rendering its sentencing decision." Penry v. Lynaugh, 492 U.S. 302, 318 (1989). Furthermore, an individual juror must be free to consider a mitigating factor, regardless of whether other members of the jury agree as to its existence. Mills v. Maryland, 486 U.S. 367 (1988); McKoy v. North Carolina, 494 U.S. 433, 442-43 (1990) ("each juror [must] be permitted to consider and give effect to mitigating evidence"). In other words, it is not enough "simply to allow the defendant to present mitigating evidence to the sentencer," rather there must not be any impediment -- through evidentiary rules,4 jury instructions5 or prosecutorial argument6 -- to the sentencer's full consideration and ability to give effect to mitigating evidence. Penry, 492 U.S. at 327-28.7
1 As Justice O'Connor noted in her concurring opinion in California v. Brown, 479 U.S. 538 (1987), evidence about the defendant's background and character is relevant because of the belief, held by this society, that defendants who commit criminal acts that are attributable to a disadvantaged background, or to emotional and mental problems, may be less culpable that defendants who have no such excuse. Id. at 545.
2 The Court stated:
Although it is true that any [favorable] inferences [drawn from the defendant's good behavior in jail] would not relate specifically to petitioner's culpability for the crime he committed, . . . there is no question but that such inferences would be 'mitigating' in the sense that they might serve 'as a basis for a sentence less than death.'
476 U.S. at 7.
3 In Delo v. Lashley, 507 U.S. 272 (1993) (per curiam), the Court implicitly acknowledged that it would violate the Eighth Amendment for a state trial court to refuse to submit to the jury a statutory mitigating circumstance which was supported by record evidence.
4 Green v. Georgia, 442 U.S. 95 (1979) (State cannot inflexibly apply its hearsay rule to exclude from penalty phase reliable hearsay evidence relevant to capital defendant's relative culpability).
5 Hitchcock, supra.
6 Penry, 492 U.S. at 326.
7 However, in Walton v. Arizona, 497 U.S. 639 (1990), the Court held that it did not violate the Eighth Amendment for a state to assign the burden of establishing the existence of a mitigating circumstance to the defendant.