The legal rights come into play exactly when the police come into the picture.

I don’t know all your amendments, but there is a thing like your 5th. just stronger: The accused is free not to help the police in any way. He may say things or remain silent, he needs not to give them things, and they may not create any kind of disadvantage for him from that. Also the court must not interpret this against him. Also spouse and family are not required to help or testify.

All of these are included in the 5th (except for subpoena of non-spouse family, but as a practical matter prosecution has a hard time forcing an unwilling family member to testify in any useful way), and on top of it the Miranda warning requirement exists to inform people of the rights. A lot of people just have a really, really difficult time shutting their mouths even when told to.