According to the bank and additional sources, two keys are required to open and close a safe. The customer possesses the primary key, but the bank keeps a reserve sealed with the customer's registered seal. The former employee, using a supervisor's authority, broke the seals of spare keys and opened the safe deposit boxes without permission. The bank said that despite employees conducting voluntary inspections of spare keys at the two branches and a group company conducting periodic inspections, they could not detect any abnormalities. To prevent a recurrence, the bank said it will review the management of spare keys. Previously, individual branches were in charge of them, but the responsibility will transfer to central management at MUFG's head office.