Legal Question in Criminal Law in California

You haven't provided enough information for answer one way or the other.

Many people believe the police always have to Mirandize anyone they arrest and that charges against the arrestee have to be dismissed if they don't. This is not how it works. A Miranda violation is not a "get out of jail free" card.

The validity of an arrest has nothing to do with Miranda warnings. Miranda only becomes a factor in court -- and even then, only if the prosecutor tries to use as evidence answers the defendant gave to police questioning while he was in custody.

Note that "in custody" does not only mean when he was behind bars; people can be in custody while the police question them at the scene and even before the police tell them they are under arrest. You say your boyfriend was "detained"; police frequently detain people in ways that don't amount to custody.

If the prosecutor ever tries to use any evidence obtained in violation of Miranda, your boyfriend should be able to have that evidence excluded. If the tainted evidence is critical to the prosecution's case, your boyfriend may get the case dismissed or win an acquittal on that basis.

But if the prosecution *doesn't* try to use such evidence -- or if there is none (because the police didn't question him improperly) -- then Miranda is a non-issue for him.

But even if your boyfriend does get some evidence excluded under Miranda, the prosecution may have plenty of other evidence it can use. That evidence may be enough to persuade a jury and, if it does, then he can be convicted.

I agree with Mr. Hoffman's response. A failure to give a Miranda warning would only mean that any statements he made while in custody could be excluded upon motion of his defense attorney. The failure to give a Miranda warning does not result in a dismissal where the prosecution has other evidence, such as eyewitness testimony, physical evidence, line up identification, etc.

Too many TV shows provide too much phony 'law' advice.

Not simply for failure to read his Miranda warnings. They don't have to do so unless and until they seek to question someone after arrest. If they sought and obtained a confession after arrest, without rights read, then he could file a Motion to Suppress that evidence.