Police have verified that illegal subcontracting took place during battery relocation work at the National Information Resources Service(NIRS) late last month, at which a fire broke out and disrupted online government services.

In a press briefing on Wednesday, the Daejeon Metropolitan Police said they are investigating whether occupational negligence and illegal subcontracting at five businesses led to the fire.

The Electrical Construction Business Act bars electrical construction companies that have won an order from subcontracting.

The battery transfer work at the NIRS, however, was carried out by a third party, rather than one of the two firms that were contracted for the job.

None of the five companies had any experience in the transfer of uninterruptible power supplies, and workers questioned by police said they did not know about a guideline on the separation and transfer of lithium batteries that advises reducing the state of charge to 30 percent or less.

Police are investigating five people for occupational negligence, including an NIRS official and an on-site manager involved in the transfer work.