United States Bill of Rights (1789), Amendment 8
" ...nor (shall) cruel or unusual punishment be inflicted."
Universal Declaration of Human Rights (1948), Article 5
"No one shall be subjected to torture or to cruel, inhumane or degrading treatment or punishment."
Geneva Conventions (1949) Article 99, Third Convention
"no moral or physical coercion may be exerted on a prisoner of war in order to admit himself guilty of the act of which he is accused "
UN Minimum Standards for the Treatment of Prisoners (1957), Rule 31
"Corporal punishment, punishment by placing in a dark cell, and all cruel, inhumane or degrading punishments shall be completely prohibited..."
International Convention on the Elimination of All Forms of Racial
Discrimination
?... to guarantee the right of everyone, without distinction to race, color or national or ethnic origin, to equality before the law, notably in the enjoyment of the following rights:
" (b) The right to security of person and protection by the State against violence or bodily harm, whether inflicted by government officials or by any individual group or institution..."
America Convention on Human Rights (1969)
"...All persons deprived of their liberty shall be treated with respect for the inherent dignity of the human person."
UN Declaration on the Protection of All Persons from Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment (1975)
"No State may permit or tolerate torture...Exceptional circumstances such as a state of war ...or any other public emergency may not be invoked as a justification of torture or other cruel inhumane or degrading treatment or punishment."
UN Code of Conduct for Law Enforcement Officials (1979), Article 5
"No law enforcement official may inflict, instigate or tolerate any act of torture...nor may any law enforcement official invoke superior order or exceptional circumstances...as a justification of torture...In this code of conduct, the term "law enforcement officials is said to include all officer of the law who exercise police powers, especially the powers of arrest or detention."
http://www.amnestyusa.org/war-on-terror/reports-statements-and-issue-briefs/us-and-international-standards-against-torture/page.do?id=1031035