TT #54 · Parashas Noach · Fourth Aliyah · Passuk 9:6
Whoever sheds the blood of man, by man shall his blood be shed, for in the image of God He made man.
Torah Temimah connects the verse to the Noachide commandment of dinim (establishment of courts).
E-Daf image — Sanhedrin 56b (size=3)
English: “By man shall his blood be shed” — from here [derives] the commandment of dinim among the seven Noachide laws: to establish courts of justice.
Custom (source for the Noachide mitzvah of dinim).
The requirement to establish courts is one of the seven mitzvot of Bnei Noach and is rooted in this verse.