A 51-year-old bus driver was arrested on Tuesday for allegedly stealing cash from four buses.

A 39-year-old staff member of New World First Bus surnamed Yuen, who was responsible for counting fares, noticed some marks on a cash box. The box seemed to have been pried open by someone at Hing Wah Street bus depot in Cheung Sha Wan in Kowloon, Oriental Daily reported.

He later found similar marks on cash boxes on three other buses. After calculating the amount of the fares taken on the buses, Yuen found that a total of HK$400 (US$50) was missing.

Yuen reported the case to the police.

After an initial investigation, police officers arrested a 51-year-old male driver surnamed Ng, who had been working for the bus company for 20 years, for alleged theft.

A bus driver union spokesperson said that every cash box is locked and secured with a cable tie that is marked with the day’s date and information about the bus.

Every bus also features a surveillance camera to capture CCTV footage of the bus driver and the cash box.