In the case of Ioannou v. New York et al., 1967, the U.S Supreme Court ruled in favor of Ioannou, a man who was convicted for refusing to answer questions before a grand jury regarding his alleged involvement in illegal gambling operations. The court held that his conviction violated his Fifth Amendment rights against self-incrimination as he had not been adequately warned about these rights prior to questioning. The state argued that since Ioannou had previously appeared before another grand jury where he was fully advised of his constitutional rights, it wasn't necessary to repeat those warnings again. However, the Supreme Court disagreed and stated that each appearance before a different grand jury is considered separate and distinct; therefore, individuals must be informed about their constitutional protections every time they appear before such bodies.

In the dissenting opinion for Ioannou v. New York et al., Justice Harlan disagreed with the majority's view that a defendant's right to counsel was violated when his lawyer was not present during a post-indictment lineup. He argued that there is no constitutional requirement for counsel to be present at every interaction between an accused and law enforcement officers, especially in situations where it would be impractical or unnecessary. Furthermore, he contended that lineups are primarily used as investigatory tools rather than prosecutorial ones and therefore do not require legal representation. In addition, he expressed concern about the potential implications of this ruling on other routine police procedures such as fingerprinting or photographing suspects.