What is the test for establishing the identity of a witness in a civil case?

United States v. Resnick (5th Cir. 1973) 483 F.2d 354, 357 (cert. den., 414 U.S. 1008, 94 S.Ct. 370, 38 L.Ed.2d 246). "Of course a witness' identity may be derived solely or principally from illegally obtained evidence and warrant a court in disallowing his testimony. . . . But the taint of the unlawful search may be removed if there are independently sufficient 'leads' by which the government may discover the identity."

Gissendanner v. Wainwright (5th Cir. 1973) 482 F.2d 1293, 1297. "Certainly, before any consequences so destructive of society's right to be protected from violent crimes is to be set in motion, there would have to be a respectable showing that (i) it was solely through such invalid source that identity was ascertained and (ii) there was no likelihood that it would have subsequently been discovered through other police efforts."