עַל־פִּ֣י שְׁנַ֣יִם עֵדִ֗ים א֛וֹ שְׁלֹשָׁ֥ה עֵדִ֖ים יוּמַ֣ת הַמֵּ֑ת לֹ֣א יוּמַ֔ת עַל־פִּ֖י עֵ֥ד אֶחָֽד׃
A person shall be put to death only on the testimony of two or more witnesses; no one shall be put to death on the testimony of a single witness.—
Torah Temimah points to Sifrei / Bavli on the phrase “the dead.”
יומת המת. וכי מת הוא והלא חי הוא, אלא המת מעיקרא, מכאן שהרשעים בחייהם קרוים מתים.
English: “The dead shall be put to death.” Is he already dead? He is still alive! Rather, [it means] one who is already dead [in a moral sense] from the outset. From here [we learn] that the wicked are called dead even while they are alive.
The paradoxical language “the dead shall be put to death” is taken as an asmakhta that the wicked are already considered dead in this world.
Derash on the verse (aggadic) — not a formal named middah of the 13. The phrasing is read as a moral characterization rather than a legal definition.
The wicked are regarded as dead even during their lifetime; the language of the verse reflects that moral reality.