Sanhedrin 4:2-3

Sanhedrin 4:2

When it comes to cases of ritual purity and impurity, they start with the most senior judge; for capital cases, they start with the most junior judge of those who sit to the side. Anyone is qualified to judge a financial case but not everyone is qualified to judge a capital case - only kohanim, Leviim and Yisroelim who are fit to marry their daughters to kohanim.

Sanhedrin 4:3

The Sanhedrin was seated in a semicircle, like half of a round threshing floor, so that the judges could see one another. Two scribes stood before them, one on either side, writing down the opinions for acquittal and conviction. Rabbi Yehuda says that there were three scribes: one wrote down the opinions for acquittal, one wrote down the opinions for conviction, and the third wrote down both opinions.