Are you saying that the police dont respond to anonymous complaints even in cases of child abuse. In many states the statute allows for anonymous complaints. The police will investigate regardless of there is a name on the complaint or not
Do you understand what hearsay is? You can only testify based on what you know not on what someone told you
Yes a pedophile can be charged with two different cases. But that is not what your original scenario was. You said that they can inform on a different municipality. Even if that person was convicted previously the prosecutor cannot use that in the instant case.