Last summer, the Supreme Court ruled 5-4 that citizens don't have a natural right to remain silent to avoid self-incrimination before they're arrested and read their Miranda rights, unless they invoke such a right. That is to say, if you are questioned by police and you haven't been arrested, what you don't say can be used against you in a court of law, unless you have the good sense to invoke your Fifth Amendment right to not incriminate yourself directly, out loud.
It was a terrible ruling, and we're seeing the consequences now in a case in the Bay Area in California. Richard Tom, speeding and possibly drunk, got into a car crash that killed a little girl in 2007. He was convicted of manslaughter, and during the trial, prosecutors used his failure to ask about the condition of the victims as evidence of his guilt. This was before he was arrested and read his rights. His conviction was challenged, but California's Supreme Court is upholding the verdict, 4-3, partly on the basis of the Salinas v. Texas case from last year. As such, because Tom failed to invoke his Fifth Amendment rights, "The prosecution may … use a defendant's prearrest silence in response to an officer's question as substantive evidence of guilt, provided the defendant has not expressly invoked the decision," the court wrote.
Maybe "Don't talk to the police" isn't enough training anymore. We may have to say "Don't talk to the police except for invoking your Fifth Amendment right not to incriminate yourself" as the new libertarian thing.
Read the court ruling here (pdf).
(Hat tip to Reason contributor Steven Greenhut)