Williams v. Illinois

Sandy Williams (defendant) was charged with rape. The prosecution's expert, forensic specialist Lambatos, testified that a DNA profile produced by an outside lab, Cellmark, from the victim's sample matched Williams's DNA, and that Cellmark was accredited. Lambatos did not describe how Cellmark created the profile, and the prosecution did not call the Cellmark analyst who made it. The trial court allowed Lambatos to assume the profile's validity, Williams was convicted, and the Illinois appellate and supreme courts affirmed; the Supreme Court granted certiorari.

Whether an expert witness may state an opinion based on facts the expert assumes, but does not personally know, to be true without violating the Confrontation Clause.