As JUSTICE SOUTER carefully explains, it is unclear whether the Alaska Legislature conceived of the State's Sex Offender Registration Act as a regulatory measure or as a penal law. See ante, at 107-109 (opinion concurring in judgment). Accordingly, in resolving whether the Act ranks as penal for ex post facto purposes, I would not demand "the clearest proof" that the statute is in effect criminal rather than civil. Instead, guided by Kennedy v. Mendoza-Martinez, 372 U. S. 144 (1963), I would neutrally evaluate the Act's purpose and effects. See id., at 168-169 (listing seven factors courts should consider "[a]bsent conclusive evidence of [legislative] intent as to the penal nature of a statute"); cf. Hudson v. United States, 522 U. S. 93, 115 (1997) (BREYER, J., concurring in judgment) ("[I]n fact if not in theory, the Court has simply applied factors of the Kennedy variety to the matter at hand.").[1]
Measured by the Mendoza-Martinez factors, I would hold Alaska's Act punitive in effect. Beyond doubt, the Act involves an "affirmative disability or restraint." 372 U. S., at 168. As JUSTICE STEVENS and JUSTICE SOUTER spell out, Alaska's Act imposes onerous and intrusive obligations on convicted sex offenders; and it exposes registrants, through aggressive public notification of their crimes, to profound humiliation and community-wide ostracism. See ante, at 109, and n. (SOUTER, J., concurring in judgment); ante, at 111-112 (STEVENS, J., dissenting in No. 01-729 and concurring in judgment in No. 01-1231).
Furthermore, the Act's requirements resemble historically common forms of punishment. See Mendoza-Martinez, 372 U. S., at 168. Its registration and reporting provisions are comparable to conditions of supervised release or parole; its public notification regimen, which permits placement of the registrant's face on a webpage under the label "Registered Sex Offender," calls to mind shaming punishments once used to mark an offender as someone to be shunned. See ante, at 111-112 (STEVENS, J., dissenting in No. 01-729 and concurring in judgment in No. 01-1231); ante, at 109 (SOUTER, J., concurring in judgment).
Telling too, as JUSTICE SOUTER observes, past crime alone, not current dangerousness, is the "touchstone" triggering the Act's obligations. Ibid. (opinion concurring in judgment); see ante, at 112-113 (STEVENS, J., dissenting in No. 01-729 and concurring in judgment in No. 01-1231). This touchstone adds to the impression that the Act retributively targets past guilt, i.e., that it "revisit[s] past crimes [more than it] prevent[s] future ones." Ante, at 109 (SOUTER, J., concurring in judgment); see Mendoza-Martinez, 372 U. S., at 168.
Tending the other way, I acknowledge, the Court has ranked some laws civil and nonpunitive although they impose significant disabilities or restraints. See, e. g., Flemming v. Nestor, 363 U. S. 603 (1960) (termination of accrued disability benefits payable to deported resident aliens); Kansas v. Hendricks, 521 U. S. 346 (1997) (civil confinement of mentally ill sex offenders). The Court has also deemed some laws nonpunitive despite "punitive aspects." See United States v. Ursery, 518 U. S. 267, 290 (1996).
What ultimately tips the balance for me is the Act's excessiveness in relation to its nonpunitive purpose. See Mendoza-Martinez, 372 U. S., at 169. As respondents concede, see Brief for Respondents 38, the Act has a legitimate civil purpose: to promote public safety by alerting the public to potentially recidivist sex offenders in the community. See ante, at 102-103 (majority opinion). But its scope notably exceeds this purpose. The Act applies to all convicted sex offenders, without regard to their future dangerousness. And the duration of the reporting requirement is keyed not to any determination of a particular offender's risk of reoffending, but to whether the offense of conviction qualified as aggravated. The reporting requirements themselves are exorbitant: The Act requires aggravated offenders to engage in perpetual quarterly reporting, even if their personal information has not changed. See ante, at 90. And meriting heaviest weight in my judgment, the Act makes no provision whatever for the possibility of rehabilitation: Offenders cannot shorten their registration or notification period, even on the clearest demonstration of rehabilitation or conclusive proof of physical incapacitation. However plain it may be that a former sex offender currently poses no threat of recidivism, he will remain subject to long-term monitoring and inescapable humiliation.
John Doe I, for example, pleaded nolo contendere to a charge of sexual abuse of a minor nine years before the Alaska Act was enacted. He successfully completed a treatment program, and gained early release on supervised probation in part because of his compliance with the program's requirements and his apparent low risk of reoffense. Brief for Respondents 1. He subsequently remarried, established a business, and was reunited with his family. Ibid. He was also granted custody of a minor daughter, based on a court's determination that he had been successfully rehabilitated. See Doe I v. Otte, 259 F. 3d 979, 983 (CA9 2001). The court's determination rested in part on psychiatric evaluations concluding that Doe had "a very low risk of re-offending" and is "not a pedophile." Ibid. (internal quotation marks omitted). Notwithstanding this strong evidence of rehabilitation, the Alaska Act requires Doe to report personal information to the State four times per year, and permits the State publicly to label him a "Registered Sex Offender" for the rest of his life.
Satisfied that the Act is ambiguous in intent and punitive in effect, I would hold its retroactive application incompatible with the Ex Post Facto Clause, and would therefore affirm the judgment of the Court of Appeals.
