How come if the criminal declines to be questioned the police cant question him?:
Without going into great detail, if you listen they say "You have the RIGHT to remain silent"   It's just the that it's their right to not have to say anything.  And when you are being questioned you aren't always a criminal, remember you must be proven guilty, but you are first innocent.  At the time when they are questioning them they are suspects.   Also i'm sure if a suspect didn't want to talk, but was forced to do so, they would make up a lot of junk and waste the polic officers time anyways