Long before ACAT came into existence, ecclesiastical authorities had protested against torture. The oldest of such interventions is found in a passage of an encyclical by Pope Nicholas in 866.
If a thief or bandit is caught, and denies what is imputed to him, you say among you that the judge should beat him on the head with blows and pierce his sides with iron spikes, until he speaks the truth. That, neither divine nor human law admits: the confession must not be forced, but spontaneous; it must not be extorted, but voluntary; lastly, if it happens that, after having inflicted these sufferings, you discover absolutely nothing concerning that with which you have charged the accused, are you not ashamed then at least, and do you not recognize how impious your judgment was? Likewise, if the accused, unable to bear such tortures, admits to crimes which he has not committed, who, I ask you, has the responsibility for such an impiety? Is it not he who forced him to such a deceitful confession? Furthermore, if some one utters with his lips what is not in his mind, it is well known that he is not confessing, he is merely speaking. Put away these things, then, and hate from the bottom of your heart what heretofore you have had the folly to practice.