Williams v. Illinois

In this case, we decide whether Crawford v. Washington, 541 U. S. 36, 50 (2004), precludes an expert witness from testifying in a manner that has long been allowed under the law of evidence. Specifically, does Crawford bar an expert from expressing an opinion based on facts about a case that have been made known to the expert but about which the expert is not competent to testify? We also decide whether Crawford substantially impedes the ability of prosecutors to introduce DNA evidence and thus may effectively relegate the prosecution in some cases to reliance on older, less reliable forms of…