While the exclusionary rule seeks to punish the police and deter police misconduct, it does carry a high costs – potentially letting the guilty escape punishment. To that end, the exclusionary rule should not put the prosecution in a worse position it would be if the misconduct had not taken place. So, if the authorities have a source leading to the discovery of the evidence independent of the misconduct (independent source), or if the evidence would have been discovered anyway (inevitable discovery), then the exclusionary rule is not applicable. And while actual, tangible evidence may be suppressed, if the police misconduct led to the discovery of a live witness, that witness testimony is typically not excluded.
Legal Supplement
Wong Sun v. U.S., 371 U.S. 471 (1963),
[T]he exclusionary rule has no application because the government learned of the evidence from an independent source …
U.S. v. Ceccolini, 435 U.S. 268 (1978),
[T]he exclusionary rule should be invoked with much greater reluctance where the claim is based on a causal relationship between the constitutional violation and the discovery of a live witness than when a similar claim is advanced to support suppression of an inanimate object.
U.S. v Crews, 445 U.S. 463 (1980),
The exclusionary rule … does not reach backward to taint information that was in official hands prior to any illegality.
Nix v. Williams, 467 U.S. 431 (1984),
[T]he derivative evidence analysis ensures that the prosecution is not put in a worse position simply because of some earlier police error or misconduct. The independent source doctrine allows admission of evidence that has been discovered by means wholly independent of any constitutional violation.
