משנה תורה, הלכות מלכים ומלחמות ט׳:י״ד

(יד) וְכֵיצַד מְצֻוִּין הֵן עַל הַדִּינִין. חַיָּבִין לְהוֹשִׁיב דַּיָּנִין וְשׁוֹפְטִים בְּכָל פֶּלֶךְ וּפֶלֶךְ לָדוּן בְּשֵׁשׁ מִצְוֹת אֵלּוּ. וּלְהַזְהִיר אֶת הָעָם.

וּבֶן נֹחַ שֶׁעָבַר עַל אַחַת מִשֶּׁבַע מִצְוֹת אֵלּוּ יֵהָרֵג בְּסַיִף. וּמִפְּנֵי זֶה נִתְחַיְּבוּ כָּל בַּעֲלֵי שְׁכֶם הֲרִיגָה. שֶׁהֲרֵי שְׁכֶם גָּזַל וְהֵם רָאוּ וְיָדְעוּ וְלֹא דָּנוּהוּ.

וּבֶן נֹחַ נֶהֱרָג בְּעֵד אֶחָד וּבְדַיָּן אֶחָד בְּלֹא הַתְרָאָה וְעַל פִּי קְרוֹבִין. אֲבָל לֹא בְּעֵדוּת אִשָּׁה. וְלֹא תָּדוּן אִשָּׁה לָהֶם:

Mishneh Torah, Kings and Wars 9:14

How must the gentiles fulfill the commandment to establish laws and courts? They are obligated to set up judges and magistrates in every major city to render judgement concerning these six mitzvot and to admonish the people regarding their observance.

A gentile who transgresses these seven commands shall be executed by decapitation. For this reason, all the inhabitants of Shechem were obligated to die. Shechem kidnapped. They observed and were aware of his deeds, but did not judge him.

A gentile is executed on the basis of the testimony of one witness and the verdict of a single judge. No warning is required. Relatives may serve as witnesses. However, a woman may not serve as a witness or a judge for them.