TOKYO (Kyodo) -- A former MUFG Bank employee who was arrested for stealing gold bars from customer safe deposit boxes is believed to have circumvented an access control system and undertaken the thefts when the bank was both open and closed, an investigative source said Thursday.

Yukari Imamura, 46, has told investigators that she turned off the system's power source before entering the safe deposit box room, the source said, a move she likely hoped would conceal her actions.

Imamura was arrested Tuesday for allegedly stealing around 20 kilograms of gold bars worth around 260 million yen ($1.6 million) deposited by two male customers at the bank's Nerima branch in Tokyo around September.

Police are continuing their investigations as they suspect Imamura stole total assets worth over 1.7 billion yen from safe deposit boxes of more than 60 customers over roughly four and a half years.

MUFG is the main banking unit of Mitsubishi UFJ Financial Group Inc.

Imamura, who has admitted to stealing the gold bars, is believed to have incurred significant losses from foreign exchange margin trading and on horse racing, according to police.

MUFG has decided to cut 30 percent of CEO Junichi Hanzawa's salary for three months over Imamura's actions. Board members responsible for managing branches will also be subject to pay cuts as a disciplinary measure, according to a separate source.

Although a large portion of her alleged thefts were committed after bank counters closed at 3 p.m., there were occasions she is believed to have stolen during bank hours, according to the investigative source.

Imamura, who was an acting branch manager, managed safe deposit boxes and is believed to have accessed spare keys stored in sealed envelopes at the Nerima branch and then resealed them with glue.