What is the effect of police questioning a defendant in an interview room without advising him of his Miranda rights?

Police questioned defendant in an interview room at a police station for two hours without advising him of his rights under Miranda v. Arizona (1966) 384 U.S. 436 (Miranda). After an hour of intense accusatory interrogation, defendant began making admissions, and he eventually confessed to many unlawful acts. Police then arrested him, advised him of his Miranda rights and, within a few minutes, obtained a second statement from defendant which merely confirmed the content of his pre-Miranda statement.