Nalanda police have registered an FIR against the owner, driver and the cleaner of the bus that caught fire on Thursday, charring to death seven persons and leaving over a dozen others nursing burn injuries.

Station house officer (SHO) of Harnaut police station Sanjay Kumar said on Friday that laxity on part of the bus owner, Randhir Kumar, and his two employees led to the blaze.

Nalanda SP Kumar Ashish had on Thursday confirmed the death of eight persons in the tragedy that occurred at Harnaut, some 60km east of Patna, around 5.30pm. However, the toll has now been revised to seven.

SHO Kumar said all the three named accused were absconding after the incident. "The police carried out intensive raids at their hideouts but they could not be arrested. Efforts are on to trace them," he said. Kumar said the identity of five of the dead had been ascertained so far. Two of them were stated to be residents of Sheikhpura, while three hail from Nalanda district. Five of the seven dead have been identified as Jairam Yadav, Bhola Yadav, Malti Devi, Moni Kumari and Pintu Kumar.

"It is difficult to ascertain the identity of the charred bodies. The DNA test will help the police ascertain the identity of the bodies which were burnt beyond recognition. Two bodies are yet to be identified," Kumar told The Telegraph over phone.

Bus owner Randhir, said to be a resident of Muraura village in Nalanda district, told some local reporters that the vehicle had been plying on the Patna-Barbigha road (Sheikhpura) route since 2014. He claimed that a technical snag could have caused the fire. The bus was travelling from Patna to Sheikhpura when the fire engulfed it.

The police, on the other hand, said preliminary investigation suggested that ammonium carbide was being carried by some passengers in the bus. "The FSL (forensic science lab) report will throw more light on the cause of the fire," SP Ashish said.

Eyewitnesses had told the investigating officials that fire erupted from the front part of the bus where the engine is located and spread very quickly. Local residents tried to douse the flames and pull out passengers by breaking open the window panes, they said.

On Thursday, Nalanda district magistrate Thiyagarajan S.M. had said a magisterial inquiry had been ordered into the incident. The probe team would comprise technical experts, who would find out the cause of the sudden fire.

Thiyagarajan said the district administration on Friday provided cheques of Rs 4 lakh to the families of the five deceased whose identity could be ascertained.

Harnaut MLA Harinarayan Singh said the driver, conductor and the cleaner of the bus fled moments after the flames surrounded the vehicle near Harnaut Thana Chowk. He said no loss of life would have happened if the emergency door of the bus had been working. "The locals pulled out the passengers by breaking the window panes of the vehicle," he added.