If they did not read him his Miranda rights, that could be enough by itself to basically throw everything out.

Sorry, but this is not correct.

First, Luigi has consistently maintained his innocence. Which obviously means he’s not admitted to any wrongdoing. If he was interrogated without being properly mirandized during a formal custodial interrogation, any statements he made during that interrogation could potentially be excluded from evidence because his constitutional rights would have been violated–but it’s not like he admitted to committing a murder during that interrogation. The evidence against him was not derived from his testimony or statements during interrogation; it was gathered independently, outside of that process.

The exclusionary rule applies to evidence obtained in violation of a defendant’s constitutional rights. If no evidence was gathered during the non-mirandized interrogation, there is nothing to exclude. While his rights may have been violated, the exclusionary rule cannot be invoked to exclude evidence that does not exist. The only scenario in which this issue would significantly impact the case is if his statements during interrogation were central to the prosecution’s case—which is not the situation here.

Furthermore, since there are no statements or testimony to exclude, even if a miranda violation occurred, it is highly likely that the court would deem the error “harmless.” This means the violation would not result in the dismissal of the case, as it does not materially affect the prosecution’s ability to present evidence or prove guilt.

Despite popular believe, not being mirandized does not immediately mean that your case gets dismissed. You have to prove that statements or evidence gathered during the offending time frame were used to convict you.