Prior to Miranda v. Arizona, in order to determine whether or not a confession was coerced such that it would be considered to have been given involuntary in violation of the 14thAmendment Due Process Clause, the courts would look at the totality of the circumstances. However, it should be noted that today, confessions are rarely deemed to be involuntary if the law enforcement officers involved conformed to the requirements of the Miranda case. Still, any Irvine criminal attorney will tell you that Miranda did not supersede the laws that bar involuntary confessions.
One of the purposes of the Miranda warnings was to inhibit the use of high-pressure tactics when obtaining a confession. The U.S. Constitution not only prohibits the use of bodily torture, but it also prohibits the use of more subtle mind-related tactics as a way of evoking a defendant’s confession against his or her will.
The Orange County Criminal Lawyer Blog

