California v. Green
United States Supreme Court
399 U.S. 149 (1970)
At Green's (defendant's) drug trial, witness Porter's trial testimony conflicted with his earlier preliminary-hearing testimony (given under oath and subject to cross-examination) and with statements he'd made to police; the prosecution introduced both the preliminary-hearing transcript and a police officer's testimony about Porter's prior statements. California's supreme court had held such prior statements inadmissible under a rule generally barring statements not previously subject to cross-examination, and California sought Supreme Court review.
Whether admitting a witness's prior statements into evidence violates the Confrontation Clause when the witness is available at trial and subject to cross-examination there.