> While you have the right to remain silent, I remember reading somewhere that you have to actively invoke that right (by stating something like "I invoke my 5th amendment right to remain silent") for your silence to be considered an invocation of that right, and not merely suspicious behavior, an implicit admission of guilt, or obstruction of justice.

This is, as I ubderstand it, incorrect on multiple levels. First, all you need to do is shut up to exercise the right. Second, no matter how you frame exercising the right, police can and will treat it as suspicious.

You may be confusing the right to remain silent with the right to have counsel present during questioning, which must be explicilty invoked for questioning without counsel present and its fruits to be excluded. They are separate, but related (as invoking the right to counsel also narrows the ways police can pressure you to waive the rightbto remain silent without legally tainting anything they get out of it.)