When is a federal court right to say as a matter of law that the state courts were wrong in their analysis of voluntariness?

Reasonable minds can and do differ about when a federal court should say as a matter of law that the state courts were wrong in their voluntariness analysis. As far back as Jackson v. Denno, 378 U.S. 368, 84 S.Ct. 1774, 12 L.Ed.2d 908 (1964), in the separate opinion of Mr. Justice Black, we find the doctrine emerging that the federal courts should "reexamine the facts to be certain that there has been no constitutional violation, and our inquiry ... cannot be cut off by fact findings at the trial level." 378 U.S. 368 at 408, 84 S.Ct. 1774 at 1797.