A witness must not serve as a judge in capital crimes

'If anyone kills a person, the murderer shall be put to death at the evidence of witnesses, but no person shall be put to death on the testimony of one witness.

Hebrew

ל כָּל-מַכֵּה-נֶפֶשׁ--לְפִי עֵדִים, יִרְצַח אֶת-הָרֹצֵחַ; וְעֵד אֶחָד, לֹא-יַעֲנֶה בְנֶפֶשׁ לָמוּת.

Greek

30 πᾶς πατάξας ψυχήν, διὰ μαρτύρων φονεύσεις τὸν φονεύσαντα, καὶ μάρτυς εἷς οὐ μαρτυρήσει ἐπὶ ψυχὴν ἀποθανεῖν.

• Parashah: Masei
• Sefer HaChinuch: 411
• Mishneh Torah: Judges — Testimony

• Numbers 35:30

Enumeration and classification from BibleData. The Greek is the Septuagint reading of the same verse, carried by the source for comparison.