The "Two Witness Rule"
Scripture tells us that we need 2 witnesses to convict a man of wrongdoing.
"One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established" (Deut 19:15)
What constitutes a "witness"? Does it have to be two people? Can non-human evidence be a "witness"? Yes, it can.
"....If it [a borrowed good] be torn in pieces, then let him bring it for witness, and he shall not make good that which was torn" (Exod/Shem 22:13)
Note here that a piece of property can be a "witness", or "evidence" as we might say in English.
"I call heaven and earth to witness against you this day, that ye shall soon utterly perish from off the land whereunto ye go over Jordan to possess it; ye shall not prolong your days upon it, but shall utterly be destroyed" (Deut 4:26)
Now earth does indeed bear witness that this happened, because there is plenty of archeological evidence left in the promised land that helps us reconstruct what happened to Israel throughout the centuries. Various remains exist to testify to what has happened. We're also told in Torah that someone can even do things that testify as a witness against themselves, when it says....
"...write ye this song for you, and teach it the children of Israel: put it in their mouths, that this song may be a witness for me against the children of Israel. For when I shall have brought them into the land which I sware unto their fathers, that floweth with milk and honey; and they shall have eaten and filled themselves, and waxen fat; then will they turn unto other gods, and serve them, and provoke me, and break my covenant" (Deut 31:19-20)
We're told here that a "song" can be a witness, and that a person singing it is bearing witness against themselves by singing it. By singing it, they testify that they knew the truth, and therefore, could not plead ignorance when the go astray and follow after other gods.
This principle was used by Solomon in his famous "baby-splitting" decision. It was a case in which two women both testified that the same child was theirs. Two witnesses did not exist - only one in each direction. But Solomon used the women's ACTIONS as a "witness" to arbitrate the tie and establish a second witness to agree with the verbal testimony of one or the other. And that decision was called a wise one by the Scriptures.
I once had someone tell me that if the police walked in and found someone standing over a dead body and he confessed to killing someone with the murder weapon in his hands, you could not convict him because there is not a second witness. That is false. The murder weapon is evidence and can be another "witness". The dead body will give off evidence as to the time of death, and if he was the only one inside that location at the time the body died, I see no reason why that could not be a second "witness". After all, if "heaven and earth" can be a "witness", then certainly a dead body can be a "witness" or "evidence" as to what happened. Yeshua also said that the miracles He performed were testimony (John 5:36). Also, a woman's reaction to the bitter waters was used as evidence against her unfaithfulness to her husband in Numbers 5.
Was the bitter water reaction a single witness? No, because it also required her husband's suspicion, which might also be a "witness" of sorts. A man is "one flesh" with his wife. If she becomes "one flesh" with another man through intercourse, he may be able to sense in his own inner being that something is amiss because he has become "one flesh" with that other man. Many people have become suspicion of their mates infidelity for precisely this reason, sensing it in their inner being, without any external evidence to suggest it. However, no suspicion is grounds for convicting anyone, but a husband's suspicion of infidelity is mentioned in Torah as reasonable cause to test his wife's faithfulness to him.
Does a confession require a second witness? Scripture records examples that suggest otherwise. Keep in mind that Torah says this...
"One witness shall not rise up against a man for any iniquity, or for any sin...." (Deut 19:15)
In other words, it seems to be written assuming that a matter is in dispute. But in 2 Samuel/Schmuel 1, David had a man put to death who confessed to killing Saul/Shaul, without a second eye-witness, a dead body, or any other supporting evidence to the contrary. While no second witness existed, Torah only requires a second witness when the first witness is rising "up against a man". The man in 2 Samuel/Schmuel 1 had confessed.
Is a person required to testify against Himself? Judaism appears to have traditionally permitted the concept that a person does not have to testify against themselves. Yeshua remained silent at His own trial and while they were amazed, they did not demand that He answer charges against Him. Yeshua did not demand that the woman accused of adultery testify against herself. She was set free because there was no other witness against her.
Are two witnesses always needed to establish ANY fact? The two witness rule is required to convict a man of sin.
In Jewish tradition, a single witness is known to be accepted in a number of situations in which a person's character is not at stake. Among them are: