Police raided the head office of Hyundai Development Company(HDC) Wednesday as part of an investigation into last week’s building collapse in the southwestern city of Gwangju that killed nine and injured eight.

The Gwangju Metropolitan Police said it sent around a dozen investigators to the HDC headquarters in Seoul on Wednesday morning. 

HDC is the contractor for the redevelopment project of the district in Gwangju where the building is located. 

Police suspect that HDC played a direct and indirect role in causing the incident by ordering a subcontractor to excessively spray water on the site to address complaints about dust, thus leading piles of earth to become waterlogged and unstable. 

Police are also looking into HDC on suspicions of sub-tier subcontracting, which is illegal in South Korea and allegations that the company has denied.