Why did the Supreme Court overturn Ernesto Miranda's conviction?

The U.S. Supreme Court overturned Ernesto Miranda’s conviction because his confession was obtained by police while he was in custody without him being informed of his constitutional rights.12

Specifically, Miranda was not told that he had the right to remain silent or that he had the right to have a lawyer present during questioning. The Court held that the prosecution could not use statements obtained during custodial interrogation unless the police followed specific procedural safeguards—now known as Miranda warnings—designed to protect an individual's Fifth Amendment privilege against self-incrimination. Because these protections were absent during his interrogation, the Court determined his conviction could not stand.123