Originally Posted by 4444

Shopkeeper's Privilege
A store owner holds the common law shopkeeper's privilege, under which he is allowed to detain a suspected shoplifter on store property for a reasonable period of time, with cause to believe that the person detained in fact committed, or attempted to commit theft of store property. The shopkeeper's privilege, although recognized in most jurisdictions, is not as broad a privilege as that of a police officer's, and therefore one must pay special attention to the temporal element -- that is, the shopkeeper may only detain the suspected criminal for a relatively short period of time. This is similar to a general right in many jurisdictions of citizen's arrest of suspected criminals by the public in limited circumstances.
Rationale
This privilege has been justified by the very practical need for some degree of protection for shopkeepers in their dealings with suspected shoplifters. Absent such privilege, a shopkeeper would be faced with the dilemma of either allowing suspects to leave without challenge.