West Bengal Director General of Police Bhupinder Singh said the police had found Pandrol clips (which tie the tracks) open along a 50-metre stretch at the accident spot and the blast theory was yet to be confirmed.
He said the Central Investigation Department has been given charge of investigation into the incident.
There have been varied reports on whether there had been a blast on the railway tracks in West Midnapore on Friday.
The railway ministry has asserted that there had been a blast on the tracks. In fact, the driver of the train had reported "explosion" to the railway officials.
Union Railway Minister Mamata Banerjee too had hinted at an explosion on the tracks.
However, Intelligence Bureau reports have ruled out the possibility saying they have not found traces of explosive along the tracks.
Preliminary investigation too have suggested the same.
According to preliminary investigations, fishplates had been found missing from a section of the track that may have led to the derailment.