The CID began its probe into the blast in East Midnapore's Egra on Wednesday by drawing up an FIR against Krishnapada Bag alias Bhanu, the owner of the illegal firework factory, his wife and son under specific sections of the Indian Penal Code and Fire Services Act but stopped short of adding specific sections under Explosive Substances Act.

Tuesday afternoon's blast had killed nine persons and injured several others at Khadikul, a village located barely 3km from the Odisha border.

Hours later, chief minister Mamata Banerjee said in Calcutta that she had no objection to a probe into the blast by the National Investigation Agency, a stance that took many of her close observers by surprise.

After gathering preliminary information, the CID sleuths drew up an FIR at the local Egra police station under different sections of the IPC, including Section 304 which refers to causing death by negligence and Section 286 that deals with negligent conduct with explosives along with specific sections under Fire Services Act.

Within hours of the FIR, it became the talking point in the state's political and administrative circles as it didn't mention specific sections under the Explosives Substances Act.

"An explosion occurred because explosive substances were stacked inside the factory. That there is no mention of the Explosive Substances Act in the FIR is unbelievable," said a senior police officer, not connected with the probe.

The BJP leaders accused the state government of tweaking the FIR in a manner so that the NIA finds it difficult to gather the basic facts of the case in case the central agency was called in to probe into the blast.

The Trinamul countered saying the CID team at work was professionally competent to unearth the truth and that there was no other objective to hide or tweak any fact related to the probe.

Several senior officers in the state administration recalled how a division bench of the Calcutta high court had handed over the probe into the alleged violence during Ram Navami processions in three districts of Bengal including Howrah, Hooghly and North Dinajpur to NIA just because the state police had not included specific sections under the Explosive Substances Act in the FIR.

The bench of the Calcutta high court while passing the order had observed that "in the cases on hand, we prima facie find that there has been a deliberate attempt on the part of the concerned police not to register any offence under the provisions of the Explosives Substances Act".

Senior police officers who have handled similar blasts in the past said any tweaking of the FIR means loss of time for the next agency that gets entrusted with the probe.

"If the NIA has to take up the Egra blast case, it will have to first draw up a fresh FIR including provisions of the Explosives Substances Act. That will be a substantial loss of time," said a senior IPS officer.

Sources in the probe team said they have gathered that the factory owner, Bhanu Bag, who is absconding, was present at the explosion site on Tuesday afternoon. Soon after the incident he called up a few villagers and left the spot in a car to possibly sneak into the adjoining state of Odisha. A team of CID officers reached Egra last night and began examining the blast site with forensic experts in tow since Wednesday morning cordoning off the area with heavy police presence.

While a set of officers from the CID's bomb disposal squad began collecting evidence another set fanned out into the village to talk to local villagers and gather information about the firework factory.

A section of local residents told officers that the factory had witnessed a similar blast in 2002 when three persons, including the owner's brother were killed. Police sources said they were looking into how the factory was allowed to run.