Mamata Banerjee on Tuesday raised questions on the efficiency of the Central Bureau of Investigation (CBI) against the backdrop of the death of Bogtui carnage accused Bara Lalon Sheikh in custody, asserting that she would go to town with the issue.

“I condemn the incident,” said the Bengal chief minister during a news conference in Shillong, Meghalaya, where she is currently on a political tour.

“And if the CBI is so smart, why is he dead? And it was inside the custody, so they (presumably, the state’s agencies) have to take the details,” added Mamata, responding to questions from journalists. “I think his (Sheikh’s) wife lodged the FIR, and we will also raise the issue.”

The Trinamul chief was referring to a complaint by Reshma Biwi who alleged her husband was murdered by the central agency’s officials, who she accused of having demanded Rs 50 lakh earlier to have his name cleared. The accusations from the victim’s wife, said several sources in Trinamul, would help bolster the party’s intense campaign to question the credibility of central agencies in the BJP regime.

Sheikh, one of the prime accused in the Bogtui carnage blamed on intra-Trinamul rivalry, died in CBI custody on Monday evening, eight days after his arrest.

Police sources said a CBI official investigating the case informed Birbhum district police that Sheikh, in his mid-40s, hanged himself with a towel inside a bathroom.

Biwi filed a complaint at the Rampurhat police station, alleging that CBI officials threatened Sheikh with murder during a team visit with him to Bogtui during an investigation process.

“My husband was murdered by CBI officials… he did not kill himself. The officials who came with him to our home, had asked for Rs 50 lakh or a (computer) hard drive to clear his name. CBI officials and CRPF personnel had been physically violent with me too, beating me up with rods,” she said. “They threatened me and our son with similar consequences.”

In her complaint demanding a probe against the CBI by the state agency CID, Biwi named three CBI officials and accused them of having tried, through “utmost mental torture”, to make Sheikh name “some big people” in the case, which she claimed he told her. She also wrote about the “immense physical torture” to extract the hard disk from him.

Although the CBI dismissed the wife’s allegations, sources said it was in trouble over the custodial death amid its ongoing probes into a number of cases in Bengal, in the face of fierce resistance from Trinamul. Several seniors in Trinamul are being investigated by central agencies, and even Mamata and Abhishek Banerjee are repeatedly threatened with incarceration in the hands of the CBI or the Enforcement Directorate by the BJP in power at the Centre.

“This has come in the form of a death, so it is not to be rejoiced. But there is no denying that this is a political windfall for us at this crucial time. It would certainly be used to corner the BJP and deter its thriving agency raj,” said a Trinamul MP. “It might also help some, like Keshto (Anubrata Mondal), secure bail,” he added.

Although in judicial custody now and not directly in the hands of central agencies, Trinamul’s Birbhum heavyweight Mondal, its sacked secretary-general Partha Chatterjee and MLA Manik Bhattacharya have been behind bars for months following their arrests by central agencies, and have repeatedly claimed worsening health.

“This has placed the BJP on the back foot, evident from the near-total silence from the otherwise vociferous saffron camp on this crucial issue,” said a state minister.

“She (Mamata) has sensed the political opportunity from this and will mount a scathing offensive,” the Trinamul added.

Trinamul state general-secretary Kunal Ghosh said custodial death was a serious matter, which needed to be probed by a high-powered committee.

“We state this unequivocally. We suspect the BJP had a role in this,” said Ghosh.

Sources in the BJP state unit also admitted, on the condition of anonymity, to Sheikh’s custodial death being “a substantial setback”.

“This (custodial death) will get in the way of us demanding CBI or ED probes at the drop of a hat,” said a state unit functionary of the BJP.

BJP state chief spokesperson Samik Bhattacharya put on a brave face.

“It is clear as daylight who is convenienced by this tragedy. We want a thorough, impartial investigation. Trinamul is in the business of CID-reliant politics, that is not so with the BJP with regard to the CBI or the ED. This is not a setback for us,” Bhattacharya claimed.