צֶ֥דֶק צֶ֖דֶק תִּרְדֹּ֑ף לְמַ֤עַן תִּֽחְיֶה֙ וְיָרַשְׁתָּ֣ אֶת־הָאָ֔רֶץ אֲשֶׁר־יְהֹוָ֥ה אֱלֹהֶ֖יךָ נֹתֵ֥ן לָֽךְ׃
Justice, justice shall you pursue, that you may thrive and occupy the land that the Eternal your God is giving you.
Torah Temimah points to Yerushalmi Sanhedrin 5:2.
Sefaria · Yerushalmi Sanhedrin 5:2
[מלמד שמצוה על ב״ד להפך בזכות בדיני נפשות]
English: [This teaches that it is a mitzvah for the court to argue in favor of the defendant in capital cases.]
The Yerushalmi links the pursuit of justice to the special obligation in capital cases to search for grounds of acquittal and to argue on behalf of the accused.
Derash on the verse (Yerushalmi) — not a formal named middah of the 13. The doubled language is taken as a directive to favor the side of life and innocence in capital proceedings.
In capital cases the court is commanded to pursue every possible argument in favor of the defendant.