Police and labor authorities have launched raids over the recent accident that killed four workers at the Gwangju Metropolitan Library construction site.

The Gwangju Metropolitan Police Agency and the Gwangju Regional Office of Employment and Labor said Saturday that they deployed about 40 police officers and labor inspectors for search and seizure operations the same day.

They searched eight locations linked to six companies, including the main contractor, Guil General Construction, and subcontractors.

Authorities said they are securing mobile phones and other evidence.

Investigators are seeking to determine whether mandatory safety measures were properly implemented.

The focus is on a patented construction method that involved pouring concrete without using temporary support structures.

Police said five people involved in the project are currently under investigation, and travel bans have been requested for eight individuals.

Given the seriousness of the case, police plan to upgrade the dedicated investigation team to a full-scale task force.

The accident happened Thursday during rooftop concrete pouring work at the construction site in Chipyeong-dong, part of the city’s Seo District.