Roy, a former TMC general secretary who joined the BJP last year following differences with party supremo Mamata Banerjee, denied the allegation, claiming that Biswas was a "victim" of the TMC's internal feud.
Amid allegations that there was no security cover despite the presence of the MLA and a minister at the venue of a Saraswati Puja where the incident occurred, the officer in-charge of local Hanskhali police station and the personal security officer of Biswas were suspended.
A departmental inquiry has also been initiated against the OC and the PSO, who was reportedly on leave on Saturday, police said. Roy is among the four persons against whom an FIR has been lodged in connection with the killing of Biswas, police said.
An officer of the West Bengal Police told media that two of the four people named in the FIR have been arrested. "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.
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"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," he said. Asked about the chances of the assailants fleeing the area, the officer said that 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.
The country-made revolver was recovered from a ground near the place of the incident. Biswas (41), who represented Krishnaganj constituency in the Assembly, was shot from a point blank range by
unidentified assailants Saturday evening inside a Saraswati puja marquee at Phoolbari area, which is about 15 km from the Bangladesh border.
He was immediately taken to a local hospital where doctors announced him "brought dead". His body was brought home from the hospital on Sunday morning for last rites, amid a blame-game between the ruling party and opposition BJP leaders over who was responsible for the death.
A large crowd gathered to pay last respects to the deceased MLA at his residence, a few metres away from the Saraswati Puja marquee where he was shot. Roy, a former TMC member of Parliament, said that the legislator's killing could be a result of infighting within the TMC.