Murder: To be Proved by Two Witnesses at Least
Source: TTT
Numbers 35:30
If anyone kills a person, the murderer is to be put to death on the testimony of the witnesses. But no one is to be put to death based on the testimony of a lone witness.
Deuteronomy 19:11, 15
If, however, a man hates his neighbor and lies in wait, attacks him and kills him, and then flees to one of these cities, / 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.