Investigators raided companies linked to the collapse at an underground tunnel construction site in Gwangmyeong, Gyeonggi Province two weeks ago that killed one person and injured another.

The Gyeonggi Nambu Provincial Police and the labor ministry began the search and seizure at builder POSCO E&C, project developer Nextrain, a subcontractor, a supervising company and others from around 9 a.m. Friday.

The police and the ministry plan to obtain documents and electronic data on the construction plan, as well as electronic devices belonging to subjects in the investigation.

The investigators intend to probe the cause of the collapse and whether safety guidelines were followed at the site.

The police have so far booked three people, each from the builder, subcontractor and supervising firm, on charges of occupational and gross negligence causing death and injury.