Prosecutors and coast guard officials searched the land ministry and one of its offices north of Tokyo last month for evidence concerning the deaths of seven people who were building port facilities off far-flung Okinotorishima Island, a barely visible coral atoll deemed part of Tokyo, sources close to the case said Friday.
The move came shortly before the Japan Coast Guard on Monday searched three Tokyo-based marine construction firms that were taking part in the project. The tiny island lies some 1,700 km south of the capital and is considered Japan's southernmost island, although it is barely visible at high tide.
A floating pier overturned off the remote island in March 2014 while the pier was under construction. Of the 16 people thrown into the sea, seven died.
The Tokyo District Public Prosecutor's Office and the Japan Coast Guard are considering whether they can build a criminal case against the parties in the construction project on suspicion of professional negligence resulting in deaths and injuries.
Last July, an investigative panel set up by the Land, Infrastructure, Transport and Tourism Ministry released an interim report saying the pier might have overturned after a crane mounted on it shifted.
The ministry office that was searched on Feb. 26 along with the ministry itself was the Kanto Regional Development Bureau, in the city of Saitama.