Every criminal case could be similarly described as one in which allowing the defendant their legally guaranteed rights (to remain silent and have legal advice) could (through strengthening the defendant's case and allowing silence on the question of co-conspirators) lead to someone depriving others of their rights (not to be victims of crime, from murder to graffiti). The question is not how to weigh these peoples' rights against each other. Instead, we have set standards on what the police are allowed to do and what the police are not allowed to do. The question is whether the police are failing to follow these standards.
As to the other questions, if an actor deprives another person of their rights, we assign the blame to the actor alone and not to any third party who allowed it to happen unless it can be proven that the third party had the intent to allow it to happen and were therefore co-conspirators in the crime. Where rights conflict, the questions of who gets which rights and who does not are answered by writing laws and judicial opinions. Several hundred years of such work has produced ready answers for most situations.
As to the other questions, if an actor deprives another person of their rights, we assign the blame to the actor alone and not to any third party who allowed it to happen unless it can be proven that the third party had the intent to allow it to happen and were therefore co-conspirators in the crime. Where rights conflict, the questions of who gets which rights and who does not are answered by writing laws and judicial opinions. Several hundred years of such work has produced ready answers for most situations.