Two senior executives at a poultry processing plant in northeastern China have been arrested over a deadly fire that killed 120 workers who were trapped behind locked exits.

Jia Yushan and Zhang Yushen, the chairman and general manager of the Baoyuanfeng factory, in Jilin province, have both been detained, local officials said Thursday, without giving further details, BBC reports.

The company’s legal representative had been held following the fire and the firm’s bank account has also been frozen, reports AFP.

Investigators said Monday’s fire, triggered by a suspected ammonia leak, was a “serious accident due to negligence” after it was found that only of the building’s doors was open at the time the fire broke out, making it difficult for the more than 300 factory workers to escape as the flames quickly spread.

The doors were apparently closed to prevent workers from taking toilet breaks, state-run broadcaster CCTV said, citing factory staff as their source.

“You had to get the team leader’s permission before going to the toilet, and the doors would only be opened then,” Li, a former worker at the factory who was only identified by his surname.