McCurry (P) challenged the constitutionality of a police search but was still convicted of drug possession despite some of the evidence being excluded based on illegal police conduct. Because he did not assert that the state courts had denied him a 'full and fair opportunity' to litigate his seizure claim, P was barred from seeking a writ of habeas corpus in a federal district court. P then filed a civil rights action for damages under 42 U.S.C. Section 1983 against the police officers involved; the search was improper. The district court held that the constitutionality of the search had already been litigated and it granted a summary judgment to dismiss the action. The court of appeals reversed; collateral estoppel and issue preclusion could not be applied in a Section 1983 action if it was the only route to a federal forum for a constitutional claim. The Supreme Court granted review.