In Cruz v. New York, 1986, the U.S Supreme Court ruled that a defendant's Sixth Amendment right to confront witnesses against him was violated when his non-testifying co-defendant's confession implicating both of them was admitted at their joint trial. The case involved two men charged with murder and robbery who were tried together. One man confessed to police but did not testify in court; his confession implicated both himself and the other man (Cruz). Despite Cruz’s objections, the judge allowed this confession as evidence during their joint trial which led to convictions for both men. However, because Cruz could not cross-examine his co-defendant about this statement since he didn't testify in court, it raised questions about violation of confrontation rights under the Sixth Amendment. The Supreme Court agreed with this argument and overturned Cruz’s conviction on grounds that admission of such confessions without an opportunity for cross-examination violates a defendant's constitutional rights.

In the dissenting opinion for Cruz v. New York, Justice O'Connor argued that the Court's decision to suppress a co-defendant's confession in a joint trial, even when limiting instructions are given to the jury, was too broad and could potentially undermine effective law enforcement. She contended that there were other ways to protect defendants' rights without such an absolute rule. For instance, she suggested allowing confessions if they were corroborated by independent evidence or permitting them if they did not directly implicate the defendant but only indirectly through inference from other facts introduced at trial. Furthermore, she believed that juries should be trusted more with handling complex evidentiary issues under appropriate judicial guidance.