BJP leader Mukul Roy was among the four people booked on Sunday in connection with the killing of Trinamul Congress MLA Satyajit Biswas in West Bengal's Nadia district, a senior police officer said.

Of the four people named in the FIR, two have been arrested, an officer of the West Bengal Police said.

Biswas, 41, who represented Krishnaganj constituency in the state assembly, was shot from point blank range by unidentified assailants Saturday evening inside a Saraswati puja marquee at Phoolbari area in the district bordering Bangladesh.

He was immediately taken to a local hospital where doctors announced him 'brought dead'.

'So far, we have arrested two persons in this case and detained another three. A country-made revolver used to shoot the MLA has also been recovered.

'As per our primary findings, it seems that the victim was fired from behind and the act was the result of a well-planned plot,' the officer said.

Asked about the chances of the assailants fleeing the area, the police officer said the state police have been put on a high alert.

'Nadia shares border with Bangladesh and there could be a possibility of them (assailants) trying to escape to the neighbouring country. Police have been put on high alert to check the movements along the border,' he said.

Roy, a former TMC member of Parliament, joined the BJP last year after his relations soured with Chief Minister Mamata Banerjee.

Claiming that the attack was a conspiracy by the BJP, TMC secretary general Partha Chatterjee said Saturday that those involved in the killing will be punished after a full- fledged inquiry.

He also said the saffron party was trying to create disturbances ahead of the Lok Sabha polls and resorted to 'politics of murder' by singling out leaders having mass bases.

The allegations were termed 'baseless' by Roy and BJP state president Dilip Ghosh.