Calcutta: Police are searching call detail records (CDR) of bus driver Sentu Biswas's mobile phone as a part of the investigation into the accident in Murshidabad.

The CDR will show if the driver was talking over the phone when the bus crashed into the railing of a bridge and plunged into the lake.

"It is very important to establish what caused an accident of this magnitude. Even if the driver is among the fatalities, we have to get to the root of the accident. We have asked the telecom service provider to supply the driver's CDR," said a senior police officer of the traffic department.

However, Sadhan Mondal who was on the bus said the driver was speaking over the phone at the time of the crash.

"The driver was continuously speaking over the mobile phone. He was holding the mobile phone in the right hand and was holding the steering with his left. The accident occurred because of the driver's lack of concentration," said Mondal.

"When the bus climbed on the Nalini Bagchi bridge, it tried to overtake a mini truck and lost control and crashed into the railing of the bridge," he added.