[2] Cap. iii, in the Mon. Germ., Leges, sect. iv, vol. ii, p. 196.
[3] Potthast, Regesta Roman. Pontif., no. 904, 1.
Their duties are outlined in a letter of Gregory IX to Conrad of Marburg, October 11, 1231: "When you arrive in a city, summon the bishops, clergy and people, and preach a solemn sermon on faith; then select certain men of good repute to help you in trying the heretics and suspects denounced before your tribunal. All who on examination are found guilty or suspected of heresy must promise to absolutely obey the commands of the Church; if they refuse, you must prosecute them, according to the statutes which we have recently promulgated." We have in these instructions all the procedure of the Inquisition: the time of grace; the call for witnesses and their testimony; the Interrogation of the Accused; the reconciliation of repentant heretics; the condemnation of obdurate heretics.
Each detail of this procedure calls for a few words of explanation.
The Inquisitor first summoned every heretic of the city to appear before him within a certain fixed time, which as a rule did not exceed thirty days. This period was called "the time of grace" (tempus gratiæ). The heretics who abjured during this period were treated with leniency. If secret heretics, they were dismissed with only a slight secret penance; if public heretics, they were exempted from the penalties of death and life imprisonment, and sentenced either to make a short pilgrimage, or to undergo one of the ordinary canonical penances.
If the heretics failed to come forward of their own accord, they were to be denounced by the Catholic people. At first the number of witnesses required to make an accusation valid was not determined; later on two were declared necessary. In the beginning, the Inquisition could only accept the testimony of men and women of good repute; and the Church for a long time maintained that no one should be admitted as an accuser who was a heretic, was excommunicated, a homicide, a thief, a sorcerer, a diviner, or the bearer of false witness. But her hatred of heresy led her later on to set aside this law, when the faith was in question. As early as the twelfth century, Gratian had declared that the testimony of infamous and heretical witnesses might be accepted in trials for heresy.[1]
[1] Pars ii, Causa ii, quaest. vii, cap. xxii; Causa vi, quaest. i, cap. xix.
The edicts of Frederic II declared that heretics could not testify in the courts, but this disability was removed when they were called upon to testify against other suspects.[1] In the beginning, the Inquisitors were loath to accept such testimony. But in 1261 Alexander IV assured them that it was lawful to do so.[2] Henceforth the testimony of a heretic was considered valid, although it was always left to the discretion of the Inquisition to reject it at will. This principle was finally incorporated into the canon law, and was enforced by constant practice. All legal exceptions were henceforth declared inoperative except that of moral enmity.[3]
[1] Historia diplomatica Frederici II, vol. iv, pp. 299, 300.
[2] Bull Consuluit, of January 23, 1261, in Eymeric, Directorium inquisitorum, Appendix, p. 40.