It is true that a police officer must read you your Miranda rights before he or she interrogates you. You do have the right to remain silent (although you may lack the capacity), and you do have the right to an attorney, and it is a pretty sure thing that whatever you tell the cop is going to be used against you. But if the cop doesn’t advise you of your Miranda rights, does the case get thrown out?
The short answer is: No.
Contrary to popular belief, the famous Miranda v. Arizona case does not mandate that the officer advise you of your rights just because you’ve been arrested. The officer only needs to advise you of your 5th Amendment right not to incriminate yourself if he or she is questioning you. If you are not being questioned, he does not need to advise you. That means that if the cop puts you in the back seat, doesn’t say a word, and you decide to confess to your string of bank robberies, you are out of luck.
Even if the officer is asking you questions, Miranda may not apply. The officer only needs to advise you of your rights if you are “in custody.” The term “in custody” is an often-litigated phrase and can be very specific to the facts of your case. But as a general rule, if you are not being detained and are free to walk away, the officer does not need to inform you of your rights under Miranda. If he passes you on the street and says, “Hi there. Rob any banks today?” and you confess to your string of bank robberies, you are out of luck.
Finally, there is a rarely-used “public safety” exception to the Miranda warnings. This exception made headlines recently after the apprehension of Boston Marathon bombing suspect Dzhokhar Tsarnaev.
If you have been arrested and are in police custody, and they are interrogating you, and there is no public safety or other exception and they forget (or “forget”) to read you your rights, then does your case gets thrown out?
Sorry, still probably not.
What will happen is that your attorney will file a “Motion to Suppress” asking the court to rule that the prosecutor may not use any of your statements at your trial. In rare cases where the prosecutor has a weak case against you and there is little evidence other than your statement, then that ruling may actually convince a prosecutor to dismiss your case or offer you a sweetheart deal. In other cases the exclusion of your statement may mean the difference between a win and a loss at trial (and the difference between freedom and many years in the slammer). On the other hand, even if the jury doesn’t hear about your confession, if you’re caught by 7 witnesses and 12 video cameras standing in a pool of blood with your hand still holding the knife in the poor corpse’s back, you’re probably still screwed.
As for Ernesto Miranda himself, the fine fellow who gave his name to one of the best-known phrases in law, he died in a knife fight in an Arizona bar with a handful of Miranda warning cards in his pocket.