Our Fifth Amendment to the United States Constitution guarantees to all people the privilege to be free from compulsory self-incrimination.
Since 1966, Miranda v. Arizona has served as the touchstone for the exploration of the scope of that privilege during a period of custodial interrogation.
Anything your son said once in custody may be subject to being suppressed.
The Court in Miranda created right to counsel procedural safeguards to adequately ensure that the accused know their rights and that the police honor them. The Miranda Court recognized that "[a]n individual swept from ... familiar surroundings into police custody, surrounded by antagonistic forces, and subjected to ... techniques of persuasion ... cannot be otherwise than under compulsion to speak."
Online we cannot know what the other details are going on in your case because online we cannot find out those details. You need a lawyer. Check with a lawyer in your locale to discuss more of the details. Failure to read his Miranda warnings means that anything he said while in custody may not be used against him as a matter of constitutional law.
Good luck to you.
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The answer to your question requires a detailed examination of the case. Many technical legal issues may be present with regard to the legality of the roadblock, whether there was probable cause for his arrest, and whether he was properly read the implied consent card before submitting to any blood, breathe, or urine analysis.
Any statements he made post arrest may be subject to suppression via Miranda, however, that depends on analyzing how the statements were made. Furthermore, in GA, Miranda does not affect consenting to a blood, breathe, or urine test.
You really should hire a DUI attorney that is well versed in these types of cases.