Twelve employees of a South Korean-owned LG Polymers plant have been arrested in connection with the chemical leak in May that killed a dozen people and hospitalised hundreds.

Business Insider India reports that police on Tuesday arrested LG Polymers Managing Director and CEO Sunkey Jeong, Technical Director D S Kim, Operations Additioanl Director P Purnachandra Mohan Rao and nine other members of staff.

In a statement obtained by Business Insider India, Visakhapatnam Commissioner of Police R K Meena said, “Investigation disclosed that the incident at M6 styrene storage tank took place due to negligence of these persons, who also have knowledge that their acts were likely to cause death.”

Toxic gas called styrene leaked from a factory run by LG Polymers, owned by LG Chem, in the city of Visakhapatnam, Andhra Pradesh state, on 7th May.

Read more: 13 dead, hundreds hospitalised following India gas leak

An investigation is ongoing.