Police were set to search the head office of Hokkaido Railway Co. on Wednesday over the railway operator's alleged falsifications of maintenance data, investigative sources said.
The search, also targeting four other locations, including JR Hokkaido's maintenance offices in Onuma and Hakodate, follows a criminal complaint the transport ministry filed against the company Monday.
The complaint by the Ministry of Land, Infrastructure, Transport and Tourism marks the first criminal case brought against a railway operator for violation of the Railway Business Act.
The Japan Transport Safety Board, in charge of accident investigations, has also accused JR Hokkaido of violating the Act for Establishment of the Japan Transport Safety Board.
JR Hokkaido is suspected of falsifying rail width data immediately after a derailment last September on its Hakodate Line as well as on the day before a special ministry audit, according to the transport ministry.
Internal investigations by JR Hokkaido have found that 129 employees out of a 795-member maintenance team had taken part in falsifying data, and falsifications were observed in 33 of 44 railway maintenance sections.
In January, JR Hokkaido announced punitive measures for 75 employees, including dismissal of five, over the failure to fix rail defects and falsification of track maintenance data.
The Hokkaido Prefectural Police are investigating the case on suspicion of professional negligence because of the failure to fix the rail defects, according to the sources.