A lone witness is not sufficient to establish any wrongdoing or sin against a man, regardless of what offense he may have committed. A matter must be established by the testimony of two or three witnesses.
Here is a statute for the preventing of frauds and perjuries; for the divine law takes care of men's rights and properties, and has made a hedge about them. Such a friend is it to human society and men's civil interest. I. A law against frauds, Deu 19:14. 1.
Commenting on Deuteronomy 19:14-21
If a false witness rise up against any man,.... In a court of judicature: to testify against him: that which is not true of him, let it be in what case it will; Aben Ezra instances in idolatry, but it holds good of any other.
TWO WITNESSES REQUIRED. (Deu 19:15) One witness shall not rise up against a man for any iniquity--The following rules to regulate the admission of testimony in public courts are founded on the principles of natural justice. A single witness shall not be admitted to the condemnation of an accused person.