If miranda v Arizona 1966 why did Ernesto Miranda say his fifth amendment Rights had been violated

The Miranda v. Arizona case in 1966 was an important case for the US Supreme Court since it established that the rights of the accused were violated when interrogated by the police custody. Miranda was convicted and the case was appealed to the Supreme Court since according to the Fifth Amendment the accused cannot make self-incriminatory confessions. Therefore, the Supreme Court overturned Miranda's conviction on the basis that his rights protected by the Fifth Amendment had been violated since he signed a written confession admitting the crime when he was under police custody.