וְהֻֽגַּד־לְךָ֖ וְשָׁמָ֑עְתָּ וְדָרַשְׁתָּ֣ הֵיטֵ֔ב וְהִנֵּ֤ה אֱמֶת֙ נָכ֣וֹן הַדָּבָ֔ר נֶעֶשְׂתָ֛ה הַתּוֹעֵבָ֥ה הַזֹּ֖את בְּיִשְׂרָאֵֽל׃
instruit du fait par ouï-dire, tu feras une enquête sévère; et si la chose est avérée, constante, si cette infamie s’est commise en Israël,
Rashi
נכון [AND, BEHOLD, IT BE TRUE, AND THE THING BE] CERTAIN — i.e. the evidence of the witnesses is in agreement (מְכֻוָּן)
Ibn Ezra
investigate well here means intensely (as in “I am greatly angry” [Jonah 4: 9]). The word well is closely related to the Hebrew word for “good”.
Tur HaArokh
והוגד לך ושמעת, “and you have been informed, and you will hear, etc.” The apparent repetition of the same thought means that whenever and wherever this accusation is brought to your attention you must immediately commence an investigation. As soon as you establish that the rumours you have heard are factual, you have to lead the guilty party to his or her place of execution where you will stone the guilty party to death.