Is there any case law in which evidence has been purged of the taint caused by the illegal seizure of documents by the federal undercover police?

We need not hold that all evidence is 'fruit of the poisonous tree' simply because it would not have come to light but for the illegal actions of the police. Rather, the more apt question in such a case is 'whether, granting establishment of the primary illegality, the evidence to which instant objection is made has been come at by exploitation of that illegality or instead by means sufficiently distinguishable to be purged of the primary taint.'

Wong Sun v. United States, 371 U.S. 471, 487-88, 83 S.Ct. 407, 417, 9 L.Ed.2d 441 (1963).

In this case, the question is whether the evidence produced by the government's subsequent undercover investigation of the sanctuary movement is sufficiently distinguishable to have been purged of the government's illegal seizure of Conger's papers. The court in United States v. Cales, 493 F.2d 1215 (9th Cir.1974), addressed a similar issue. An illegal wiretap triggered an investigation which had long been dormant. Id. at 1215. The revived investigation produced evidence that prompted the government to seek defendant's conviction for income tax evasion.