Parashas Masei · Passuk 35:12 · TT note 2
Chabad.org — English translation + Rashi
Torah Temimah points to Makkos 12a (TT note on “עַד עׇמְדוֹ לִפְנֵי הָעֵדָה”).
English: It was taught: Rabbi Akiva says, from where [do we know] that a Sanhedrin that itself saw someone kill a person may not put him to death until he stands in another court? From “until he stands before the congregation for judgment” — until he stands in another court.
Halakhic requirement of a separate trial court even when the judges were eyewitnesses.
Judges who witnessed a killing may not themselves execute the killer; he must stand trial before a different court.