Deuteronomy 19:15

15 One witness is never enough to convict someone of a crime, offense, or sin he may have committed. Cases must be settled based on the testimony of two or three witnesses.

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 They must have no pity on him. The guilt of murdering an innocent person must be removed from Israel. Then things will go well for Israel.

14 Never move your neighbor's original boundary marker on any property in the land that the LORD your God is giving you.

15 One witness is never enough to convict someone of a crime, offense, or sin he may have committed. Cases must be settled based on the testimony of two or three witnesses.

16 This is what you must do whenever a witness takes the stand to accuse a person falsely of a crime.

17 The two people involved must stand in the LORD's presence, in front of the priests and judges who are serving at that time.