Malleus Maleficarum Part 3
Of the Solemn Adjuration and Re-examination of Witnesses
But it may be asked whether the Judge can compel witnesses to sweat an oath to tell the truth in a case concerning the Faith or witches, of if he can examine them many times. We answer that he can do so, especially an ecclesiastical Judge, and that in ecclesiastical cases witnesses can be compelled to speak the truth, and this on oath, since otherwise their evidence would not be valid. For the Canon Law says: The Archbishop or Bishop may make a circuit of the parish in which it is rumoured that there are heretics, and compel three or more men of good repute, or even, if it seems good to him, the whole neighbourhood, to give evidence. And if any through damnable obstinacy stubbornly refuse to take the oath, they shall on that account be considered as heretics.
And that the witnesses can be examined several times is shown by the Canon, where it says that, when the witnesses have given their evidence in a confused manner, or appear to have withheld part of their knowledge for some reason, the Judge must take care to examine them afresh; for he may legally do so.
Of the Quality and Condition of Witnesses