The Mekhilta addresses a critical question in Jewish criminal law: what happens when new incriminating evidence emerges after a defendant has already been acquitted? The Torah states, "A clean one you shall not kill" (Exodus 23:7), and the rabbis derive from this a principle that may seem surprising.
If a person left the court having been found innocent, and afterward some new evidence of guilt was discovered, one might assume the court would simply retry him. Bring him back, present the new evidence, and render a new verdict. The Mekhilta rejects this possibility. The verse "a clean one you shall not kill" means that once a person has been declared clean, declared innocent by the court, he cannot be returned for further prosecution on the same charge.
This ruling establishes something remarkably close to what modern legal systems call "double jeopardy," the principle that a person cannot be tried twice for the same crime. The rabbis arrived at this conclusion not from philosophical reasoning about fairness but from a direct reading of Scripture. God commands: do not kill someone who has been declared clean. A court verdict of innocence, once rendered, carries the force of divine law.
The Mekhilta introduces this with the word "variantly," indicating it is one of several interpretations of the same verse. Other readings apply the principle differently. But this particular interpretation demonstrates the sages' deep concern for protecting the individual against the power of the state. Even if the court later realizes it may have erred, the acquitted person walks free. The finality of an acquittal is absolute.