Justice Marshall first questioned the Court's jurisdiction. He argued that Salerno's unrelated conviction and 100-year sentence, together with Cafaro's release on a personal-recognizance bond after becoming a cooperating witness, strongly suggested that neither respondent remained subject to an actual detention controversy. In his view, the Government had failed to disclose or adequately confront facts that could make the case moot.
Marshall rejected the majority's regulatory-versus-punitive framework as too narrow. A measure does not become constitutionally permissible merely because Congress describes its purpose as regulatory. Otherwise, he argued, Congress could impose sweeping restraints on people thought statistically likely to commit crimes, such as a nighttime curfew on unemployed persons, so long as it invoked public safety rather than punishment.
He maintained that the Due Process Clause and the Excessive Bail Clause must be read together because both protect the presumption of innocence. Denying bail has the same practical effect as setting bail at an unattainable amount, and the Eighth Amendment constrains Congress as well as judges. The Government may restrain an accused to assure appearance at trial or prevent obstruction of the judicial process, but not to imprison a legally innocent person for anticipated, uncharged crimes.
In Marshall's view, the Act makes an indictment function as evidence that an accused will commit future crimes. Yet a person is as legally innocent before trial as after an acquittal; if an acquittal would end preventive detention, the indictment cannot constitutionally justify it in the first place. The statute therefore undermines the presumption of innocence while allowing potentially indefinite incarceration based on predictive judgments rather than proof of guilt beyond a reasonable doubt.
Marshall warned that the Government's willingness to release Cafaro once he became an informant illustrated the coercive power and abuse potential of preventive detention. Constitutional protections must apply even to defendants whom the Government portrays as dangerous, because shortcuts taken against the accused ultimately threaten innocent people and the liberty of all.