Rashi on Deuteronomy 19:20/רש"י על דברים י״ט:כ׳

1ישמעו ויראו [AND THOSE WHO REMAIN] SHALL HEAR AND FEAR — From here we derive the law that a public announcement is required: “The men named so-and-so are to be executed because they have been convicted by the court as “plotting witnesses” (Sanhedrin 89a).