You initiate an investigation of whether an incorrect change of holder has taken place. As a registrar, you are obligated to store all data regarding change of holders so that you can use the documentation for an investigation of whether a incorrect change of holder has taken place. If a registrant reports that a change of holder was improperly conducted, the saved data is checked.
Remember that the new Registrant may have acquired the name in good faith and you should not personally decide on a possible reversal of the domain name, but rather urge the previous registrant to file a police report (on suspicion of a crime) or have the matter tried as a dispute in court.
