The Fourth Amendment prohibits unreasonable searches and seizures. When evidence is found or seized during an unconstitutional search or seizure, the evidence is generally not admissible in Court. This is known as the exclusionary rule.
Typically, the exclusionary rule is enforced by litigating a motion to suppress. That is, a defendant must file a motion to suppress the evidence and the government has the burden of proving that the evidence was not seized in violation of the Constitution. If a defendant is unsatisfied with the trial court’s disposition of the motion, the issue of suppression may be raised again on direct appeal and (potentially) during state post-conviction proceedings.
However, the application of the exclusionary rule to evidence seized in violation of the Fourth Amendment is generally not litigated on federal habeas corpus review. In Stone v. Powell, 428 U.S. 465 (1976), the United States Supreme Court held that a state prisoner may not be granted federal habeas corpus relief on the ground that evidence obtained in an unconstitutional search or seizure was introduced at his trial. According to the Supreme Court, the rationale for their holding was the minimal deterrent effect on law enforcement in relation to the costs of doing so.
There are two exceptions to this rule. First, the Supreme Court in Powell explicitly limited the rule to those situations in which the State provided an opportunity for full and fair litigation of a Fourth Amendment claim. In other words, if a state prisoner can convince a federal habeas court that he or she was denied a meaningful opportunity to litigate his or her Fourth Amendment challenge, the Stone rule will not prevent the petitioner from raising the issue in a habeas corpus proceeding. Second, suppression issues can be tangentially raised under the Sixth Amendment and a claim of ineffective assistance of counsel. For example, a habeas petitioner could challenge counsel’s failure to seek suppression on his or her behalf or the effectiveness of counsel’s representation during the litigation of his or her suppression motion. In either of these two scenarios, the probable merits of the suppression issue would need to be established for the petitioner to be entitled to relief.