TT #236 · Parashas Shoftim · Sixth Aliyah · Passuk 19:15
A single witness shall not rise up against a man for any iniquity or for any sin, in any sin that he may commit; by the mouth of two witnesses or by the mouth of three witnesses a matter shall be established.
Torah Temimah points to Sanhedrin 30b.
TT lemma: עַל פִּי שְׁנֵי עֵדִים.
English: ‘By the mouth of two witnesses’ – that both of them see as one.
Derash on joint perception (Bavli) — the ideal is that the witnesses experience the event together.
The preferred form of testimony is that the two witnesses observe the event together, so that their accounts form a single coordinated whole.