In a world without McNabb-Mallory, federal agents would be free to question suspects for extended periods before bringing them out in the open, and we have always known what custodial secrecy leads to,” Justice Souter wrote. “No one with any smattering of the history of 20th Century dictatorships needs a lecture on the subject…and there is mounting empirical evidence that these pressures can induce a frighteningly high percentage of people to confess to crimes they never committed.”

...Justice Frankfurter’s point in McNabb is as fresh as ever: “The history of liberty has largely been the history of observance of procedural safeguards.” 318 U. S., at 347. McNabb-Mallory is one of them, and neither the text nor the history of §3501 makes out a case that Congress meant to do away with it.

Under the rule as revised by §3501(c), a district court with a suppression claim must find whether the defendant confessed within six hours of arrest (unless a longer delay was “reasonable considering the means of transportation and the distance to be traveled to the near-est available [magistrate]”). If the confession came within that period, it is admissible, subject to the other Rules of Evidence, so long as it was “made voluntarily and . . . the weight to be given [it] is left to the jury.” Ibid.

If the confession occurred before presentment and beyond six hours, however, the court must decide whether delaying that long was unreasonable or unnecessary under the McNabb-Mallory cases, and if it was, the confession is to be suppressed.

The decision was 5 to 4. Who dissented? Alito, Scalia and Thomas.