I assume that a custodial interrogation that involved the use of "torture" would be suppressed by any U.S. court.
But I can't find a law that clearly defines custodial practices that would constitute torture, beyond the "Torture Act."
In researching this I have found frequent references to "cruel, inhumane, or degrading treatment." Is there precedent for suppression of interrogation conducted under conditions in which a detainee has been subject to "cruel, inhumane, or degrading treatment?"
One condition that is enumerated, at least by the DoD, is hypothermia. Another I imagine to be more common would be sleep deprivation, if for no other reason than that it impairs an individual's ability to assert one's Miranda rights.