Does the exclusionary rule of the Fourth Amendment apply to the federal courts?

Our decision in Gates v. Henderson, supra, refusing to permit litigation of a fourth amendment claim, even where the state appellate courts had refused to hear it, did not depend upon state invocation of a procedural bar. Rather, we were satisfied that Stone v. Powell, supra, had foreclosed federal habeas review of exclusionary rule contentions except in the rare case where the state provided no corrective procedures at all, or there had been an "unconscionable breakdown" in state process which prevented utilization of an existing procedural remedy. Gates, supra, 568 F.2d at 840. The conceptual basis of Stone v. Powell ² compelled our conclusion: "To permit a hearing now[, many] years later, after memories have long since dimmed, to determine what cause the police had at that time to make an arrest would be neither just to society nor effectuate the rationale of the exclusionary rule--police deterrence." Id.