The Federal Circuit has affirmed a decision by District of Delaware Chief Judge Gregory M. Sleet. Following a bench trial, the district court held that prosecution history estoppel barred the patentee from asserting the doctrine of equivalents as its infringement theory. The district court also rejected assertions of unforeseeability and tangentiality in the claim-narrowing process, both of which, if proved, would have precluded the estoppel finding.
In its affirming opinion, the CAFC agreed with the district court’s conclusion that, on the issue of foreseeability, endorsing one of the parties’ experts over the other “was not close.” Quoting the Supreme Court, the appellate court reminded its readers of the discretion vested in trial judges:
[W]hen a trial judge’s finding is based on his decision to credit the testimony of one of two or more witnesses, each of whom has told a coherent and facially plausible story that is not contradicted by extrinsic evidence, that finding, if not internally inconsistent, can virtually never be clear error. (Op. at 16)
This makes sense: It is the jurist that presides at trial, and not the appellate judge, that is the frontline decision maker. With the CAFC coming under fire in recent years for its alleged meddling with the work of the trial judges, this opinion, at least, demonstrates the value this circuit court places on credibility determinations – and the work of the district courts.