HWASEONG (Yonhap News) ― A total of seven people, including three officials of Samsung Electronics Co.’s chip plant, have been indicted on charges of professional negligence that led to last month’s fatal hydrofluoric acid gas leak, police said Tuesday.

Up to 10 liters of diluted hydrofluoric acid, a colorless acute poison that can damage the lungs and bones and even affect the nervous system, leaked from one of the valves at the main semiconductor factory of the world’s largest memory chip maker in Hwaseong, 60 kilometers south of Seoul, on Jan. 27.

The leak killed one maintenance crew member from the STI Service ― Samsung’s subcontractor ― and injured four others.

Announcing a preliminary outcome of the probe, the Gyeonggi Provincial Police Agency said they have brought charges against three Samsung officials, including an executive director of the Hwaseong site surnamed Choi, and four STI workers on suspicion of safety negligence and belatedly reporting the incident to authorities.

Citing forensic evidence, police said the cause of the leak is suspected to be the corrosion of one of the valves inside the Central Chemical Supply System (CCSS) of the chip plant.

“We have also summoned Samsung Electronics’ chief in charge of the Hwaseong site for questioning, but he has not yet responded,” a police officer leading the investigation said, adding the police will review whether to bring further charges against others.

Police, however, said they have not yet clarified whether the world’s largest chip maker purposely discharged the toxic gas from the factory into the environment.

With the cooperation of the Ministry of Environment and the provincial government of Gyeonggi, to which Hwaseong belongs, police launched a special investigation into the incident. The investigation focuses on whether Samsung properly managed and monitored the chemical substances.

The outcome is expected to come out sometime next month, a ministry official said.

Also, police said they have not yet clarified the extent of the secondary damage caused by the leakage.

Samsung, which has been under intense fire for not only failing to report the incident to the authorities promptly but for also allegedly covering up the incident, issued an apology.

“We offer an apology to the bereaved family (of the victim) and the people,” the chipmaker said in a release. “We will try our best to prevent the repeat of such an incident.”