Mattox v. United States

After Mattox's (defendant's) first murder conviction was reversed and remanded for a new trial, two witnesses who had testified against him at the first trial - and whom he'd had the opportunity to cross-examine there - died before the second trial; their prior testimony was read into evidence at the retrial, and Mattox was convicted again, appealing on the ground that admitting the dead witnesses' prior testimony violated his constitutional right to confront the witnesses against him.