Deuteronomy 19:15

15 You cannot convict anyone of a crime or sin on the word of one witness. You need two or three witnesses to make a case.

Deuteronomy 19:15 Meaning and Commentary

Deuteronomy 19:15

One witness shall not rise up against a man for any iniquity,
or for any sin, in any sin that he sinneth
Whether capital sins, or pecuniary debts; or whatsoever sins a man may be guilty of whether sins against the first or second table of the law, whether greater or lesser sins, whether in moral or civil things; the Jews except only in the case of a woman suspected of adultery and of beheading the heifer:

at the mouth of two witnesses, or at the mouth of three witnesses,
shall the matter be established;
either for acquittance or condemnation; and the witnesses may not, as Jarchi says, write their testimony in a letter, and send it to the sanhedrim, nor may an interpreter stand between the witnesses and the judges; (See Gill on Deuteronomy 17:6).

Deuteronomy 19:15 In-Context

13 Don't feel sorry for him. Clean out the pollution of wrongful murder from Israel so that you'll be able to live well and breathe clean air.
14 Don't move your neighbor's boundary markers, the longstanding landmarks set up by your pioneer ancestors defining their property.
15 You cannot convict anyone of a crime or sin on the word of one witness. You need two or three witnesses to make a case.
16 If a hostile witness stands to accuse someone of a wrong,
17 then both parties involved in the quarrel must stand in the Presence of God before the priests and judges who are in office at that time.