Legally speaking, an act of torture committed by a US citizen outside of the US is punishable under 18 USC 2340. The definition of torture used in this statute includes:
'torture' means an act committed by a person ... specifically intended to inflict severe physical or mental pain or suffering ... upon another person in his custody or physical control.
And this includes:
the administration or application, or threatened administration or application, of mind-altering substances or other procedures calculated to disrupt profoundly the senses or personality.
A two year study by the US independent group, The Constitution Project, concluded that it was 'indisputable' that the US forces had used torture as well as 'cruel, degrading and inhuman treatment' in many interrogations.
And that 'the nations most senior officials' bear ultimate responsibility for allowing and contributing to the spread of these techniques and that there was substantial evidence that the information gained by these techniques were neither reliable or useful.
Whilst Amnesty International and others have criticised the Military Commissions Act of 2006 for approving a system that uses torture and for destroying mechanisms for judicial review created by Hamdan vs Rumsfeld and for creating a parallel legal system below international standards.
Also, in 2008, an independent commission chaired the former Secretary of Defense, James Schlesinger, reported that what took place at Abu Gharib prison, later renamed Baghdad Prison, was due to the 'sadism' on part of the officers working the night shift, but that also responsibility for the 'mistreatment' of prisoners went higher up the chain of command back to Washington.