Re: I don't get it...
That's because you, like many people in this day and age, are assuming that the fifth amendment is in place to protect the guilty. It's not. It is there to protect the innocent. You can easily incriminate yourself without actually being guilty without such protection.
An example: someone you dislike very strongly was found dead in a bathroom in a bar. You happened to be at the bar at the time, but weren't involved. In the course of investigating, the police ask you how you felt about that person. Lying to a cop is a bad idea, and admitting you hated the guy puts you on a short list of suspects, so you plead the fifth (if you're smart).
The thing to remember about the American justice system is that it's built around the idea that it's better to let a guilty man go than to imprision an innocent one. That's why it sometimes seems like the criminals have more rights than the victims: a lot of the time they do.