Paucapalea (ca. 1150), Prologue to Summa, ed. Johann F. von Schulte (Giessen: 1890, repr. Aalen: 1965) 1:

Placitandi forma in paradiso primum videtur inventa, dum prothoplastus ^┌de inobedientiae crimine ibidem a domino interrogatus^┐ criminis relatione sive remotione usus culpam in coniugem removisse autumat dicens, "Mulier, quam dedisti, dedit mihi et comedi" (Genesis 3.12).  Deinde in veteri lege nobis tradita cum Moyses in lege sua ait: "In ore duorum vel trium testium stabit omne verbum" (Deut. 19:15 and 2 Corinthians 13)

The form of pleading was first found in paradise when the first man was questioned about the crime of disobedience.  When the Lord questioned him about the report of the crime or of use he transfered the guilt to his wife by asserting "The wife whom you gave to me handed it to me and I ate it." Whence in the Old Testament it is given to us when Moses declared his law: The truth will be found in the testimony of two or three witnesses.