The Haryana government has formed a four-member panel to investigate a school bus crash that killed six students and injured 20 in Mahendragarh district, NDTV reported on Friday.

The accident occurred on Thursday near Unhani village in Kanina when the bus collided with a tree and overturned. The state government later ordered an investigation after reports emerged that the driver was allegedly drunk and that the bus did not have a fitness certificate, reported PTI.

The government also issued a show-cause notice to the school as it remained open on Thursday despite it being a public holiday. Seema Trikha, Haryana education minister, said that the biggest lapse leading to the accident was that the school remained open on Eid.

Three persons, including the school’s principal and another official, have been arrested in the case.

State transport minister Aseem Goel told reporters that the owner of the bus had recently been fined Rs 15,000 for not having certain documents in order. The vehicle being put into operation was a lapse on the part of the school authorities, he said.

Goel also promised action against the area’s motor vehicle inspector if the investigation found him to be complicit in the accident. The minister said he has ordered that the fitness certificates of all school buses in Haryana to be checked.