Five people have been charged with professional negligence after a devastating fire at a government data center in South Korea last month, which police believe started when unqualified workers tried to move a battery.

The fire at the National Information Resources Service (NIRS) center in Daejeon, South Korea, on September 26 destroyed 384 battery cells and multiple servers, and left the vast majority of Korea’s digital public services offline. According to officials, 60 percent of services have now been restored, but work continues to bring other systems back online.

While recovery work continues, Daejeon Metropolitan Police Agency has been investigating how the fire started, and according to a statement reported by Korea JoongAng Daily, five people have now been charged with professional negligence relating to the fire. Four people had previously been held in connection with the incident.

One NIRS official, one worker from a project management firm, and three employees of construction companies have been charged, police said. In total, they questioned 29 people about the fire.

The fire started during work to move lithium-ion UPS batteries from a data hall on the fifth floor to the building’s basement.

As previously reported by DCD, witness testimony provided to the police said that though the main power to the building was disconnected when the fire broke out, an auxiliary power system connected to the data center’s Uninterruptible Power Supply (UPS) battery backup system was not.

Investigators said that workers failed to follow safety protocols, didn’t use the required insulation materials, and failed to fully discharge the batteries before moving them, increasing the risk of fire. The staff involved were not qualified for the job, had no experience in battery relocation, and the contractors on the project did not involve the battery manufacturers in a bid to cut costs.

What’s more, the battery relocation work had been illegally subcontracted, with the two companies that won the tender for the project having handed it off to three other businesses, in contravention of Korean law. The two primary contractors falsified employment records to make it look like the staff on the project worked for them directly, police claim.

The investigation into the fire is due to conclude in November, and officers are considering whether charges should be brought against the contracting firms.

“While the precise cause of the fire will be determined after forensic analysis, we will continue to investigate the rule violations and illegal subcontracting, and those responsible will be held accountable,” a police official said.

Though most public services are now back online, fallout from the fire is likely to continue for some time. It is thought that up to 858TB of government data, stored on a drive destroyed in the fire that was not backed up, has been lost for good.