Have you ever wondered why store security can detain a shoplifter?

Some people have asked me why/how store security can detain a shoplifter, since they are not the police? he is how it works. most states have citizen arrest laws, which allow a private citizen to make a citizens arrest for certain violations of the law. this is covered under shoplifting, provided the police are notified and the person is arrested. some stores do not call the police, but rather have the suspect sign a release of liability and promise to never enter their store again. the store property is recovered and thats it. some stores believe in prosecution and the police are called. a report is made and store security follows the police to the magistrate for prosecution. security guards have very limited power and within a certain area only. security guards are not police officers. here is my question: do you believe that security guards are necessary for the protection of a company’s safety and its mechandise?