TOKYO (Kyodo) -- A former MUFG Bank employee who was arrested for allegedly 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.

MUFG, the main banking unit of Mitsubishi UFJ Financial Group Inc., said Thursday that Imamura stole assets, including cash and gold bars, worth around 1.4 billion yen from the safe deposit boxes of some 70 customers at two of its branches.

It has compensated 40 customers a total of some 700 million yen to date and is considering filing a damages lawsuit against Imamura.

Police are continuing their investigations and estimate the total market value of the stolen items to exceed 1.7 billion yen.

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. Chairman Naoki Hori and three other executives will also be subject to pay cuts as a disciplinary measure, the bank said.

The bank also intends to install security cameras in rooms containing safe deposit boxes, as well as make its screening process for promotions to managerial positions more stringent.

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.

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.

She also allegedly took photos of the safe deposit boxes prior to opening them so she could return them to their original state, with around 800 such images found on her phone, the source said.