Suvendu Adhikari on Thursday claimed that had he not defeated Mamata Banerjee from Bhabanipur, his personal assistant Chandranath Rath would not have been murdered, appearing to imply a Trinamool hand in the assassination.

Some other BJP leaders suggested a possible role by Bangladeshi radical groups, citing the sophistication of the attack and its timing — three days before the swearing-in, to be attended by Prime Minister Narendra Modi — and the location, fairly close to the border.

“His (Rath’s) only fault was being the PA of Suvendu Adhikari. So, he was brutally shot by contract killers who had tracked his movements for the past four days,” Suvendu said at the Barasat hospital where Rath's post-mortem was done.

“Had I not been leader of the Opposition, he would not have been targeted. He would not have been targeted had I not defeated Mamata Banerjee from Bhabanipur.

“I’m suffering from deep mental anguish. I request the police and other agencies involved in the investigation to identify and ensure capital punishment for all those behind the killing.”

The assassination of Rath, who had been working with Suvendu for the past eight years, has shocked the BJP dispensation at a time the party has been urging its ranks to maintain peace amid the reports of post-poll violence across the state.

Before Suvendu’s comments, several other BJP leaders had blamed Trinamool for the murder, accusing it of trying to keep the law-and-order situation volatile. But some others speculated about the possible involvement of fundamentalist groups such as the Jamaat-e-Islami of Bangladesh.

“We doubt that such a planned killing could merely be part of the post-poll violence,” a senior BJP leader said.

The BJP leader added: “We suspect this murder was, rather, a message from the fundamentalist forces against whom Suvendu had campaigned extensively in the run-up to the elections.”

State BJP president Samik Bhattacharya, who too visited the Barasat hospital on Thursday, flagged Madhyamgram’s proximity to the border, and said “infiltrators” had been using “safe houses” in the region for years. Madhyamgram is 65km from the Bangladesh border.

“In the past 15 years, the TMC has completed the politicisation of criminals and made them fearless. Barasat and Madhyamgram are not far from the Bangladesh border,” Samik said.

“A lot of illegal activities have been carried out from this zone. Infiltrators arrested from different parts of the country have admitted they obtained forged documents like Aadhaar cards and ration cards through people living in these areas.”

He added: “This is a very sensitive area. So, I’m asking whether this murder was meant to send a message to Prime Minister Narendra Modi, who will come here for the swearing-in on Saturday….”

Asked whether he suspected the involvement of Bangladeshi fundamentalist groups and “infiltrators”, Samik told The Telegraph: “Police should investigate that angle as well. There may be involvement of the TMC, such groups, or both.”

BJP insiders said some recently circulated videos had shown a Bangladeshi MP expressing concern about a possible saffron victory in the Bengal elections.

Rath may have been killed to send a message to Suvendu, who had campaigned aggressively against “infiltrators”, Rohingyas and illegal Bangladeshi immigrants, a source said. It may have been a signal that such forces still have a presence in Bengal, he added.

“However, once the government is formed, every step to drive out infiltrators will be taken, as our leader Amit Shah has promised,” a senior BJP leader in Calcutta said.

He claimed the murder may also have been an attempt to instigate violence in the state for political gain at a time when BJP leaders were trying to prevent post-poll clashes.

A senior police officer associated with the probe said no angle would be ignored, adding that the investigators suspected “a grave conspiracy” behind the murder.

“It’s clear the murder was meticulously planned and carried out as part of a grave conspiracy. Though it’s too early to determine the exact motive, we are examining every possible angle, including the claims made by BJP leaders,” he said.

As evidence of how carefully the murder was planned, he said the motorbike recovered near the airport did not have its original number plate.

“The chassis and engine numbers of both the motorbike and the car seized so far had been tampered with. Highly professional criminals used sharpshooters armed with modern firearms to kill Adhikari’s PA,” he said.