It is not as if anti-torture ideas are new.  Philosophers, ethicists, and political thinkers throughout history have understood that a truly free society can not exist if torture is allowed.  Here are some links to some important documents outlining these principles.

The Bill of Rights to the Constitution of the United States and the Universal Declaration of Human Rights explicitly forbid torture.  Here are the links to the texts of these foundational documents:

The Bill of Rights

Text of the Universal Declaration of Human Rights

 An Italian lawyer, Cesare Bonesana, the Marquis Beccaria of Milan (1738-1794) , wrote an excellent treatise concerning crime and punishment in which he deals extensively with torture.  It is one of the most extensive treatments of torture from the Enlightenment era and was quite popular in Europe at the time.  It was probably influential in the numerous torture bans that were enacted by European governments during the 18th century.  It is a wonderful example of Enlightenment scholarship and you can find it in its entirety at this link:

Of Crimes and Punishments

The Stanford Encyclopaedia of Philosophy has an excellent entry on torture.  It is not a historical document, but it does provide a clear definition of what torture actually is and an account of the philosophical debate surrounding it.  As a student of philosophy myself, I think that it is crucial that we define our terms clearly when engaging in discourse.  This is why I included it here:

Stanford Encyclopaedia of Philosophy Entry on Torture