What is the difference between a written confession and an oral confession?

Respondent was not questioned between the two confessions nor does he complain of any mistreatment. The sole ground respondent asserts for suppression of his written confession is that his previous oral confession was secured in violation of his Miranda rights and that his waiver of such rights in the police-station was influenced by the fact that he had through his illegally obtained confession already 'let the cat out of the bag.' (See United States v. Bayer, 331 U.S. 532, 540, 67 S.Ct. 1394, 1398, 91 L.Ed. 1654, for this often-cited dictum.)