Bara Lalon Sheikh, one of the prime accused in the March 21 Bogtui carnage that has been blamed on intra-Trinamul rivalry, died in CBI custody on Monday evening, eight days after his arrest.

His family accused the central agency of “murdering” him at its camp office in Rampurhat, Birbhum. Police sources said a CBI officer investigating the case had informed Birbhum district police that Sheikh, a man in his mid-40s, had hanged himself with a towel inside a bathroom.

“The CBI informed us about the death of a person in their custody. They claimed it was suicide by hanging. However, we shall probe the matter,” Birbhum police chief Nagendra Nath Tripathi said.

Police sources said Sheikh’s body would be sent for a post-mortem on Tuesday to find out the actual cause of death.

Sources said the custody death is an embarrassment for the CBI at a time it faces accusations of bias from Bengal’s ruling Trinamul, several of whose leaders are being probed by central agencies. Sheikh was arrested and produced at Rampurhat court on December 4 from a hideout in Jharkhand, eight months after the March 21 massacre of 10 people in Bogtui, Birbhum.

He was sent to six days’ CBI custody and later for another three days. The CBI was supposed to produce him before the Rampurhat court again on Tuesday.

Sheikh was a known associate of the deputy chief of a Trinamul-run gram panchayat, Bhadu Sheikh, whose murder on March 21 had reportedly prompted his supporters to massacre his known intra-party opponents in Bogtui. Sheikh’s family alleged he had been tortured to death.

“The CBI came and ransacked our house today in the name of investigation. They also beat me up,” Sheikh’s wife Reshma Biwi said. “The CBI officials threatened to kill my husband. I want to see those officials punished as they killed my husband intentionally.”

Reshma and other family members said they would lodge a murder complaint against the CBI. Police officers said a case would be registered after the family lodged a complaint.

A large police team has been deployed in Bogtui village and near the CBI camp office on the outskirts of Rampurhat town. Trinamul demanded a high-level enquiry to find out whether the BJP had a hand in the death.

“Death in CBI custody is a serious matter and should be probed by a high-level committee. We suspect the BJP may have had a role as their leaders always forecast the activities of the CBI,” Trinamul spokesperson Kunal Ghosh said.

“Suvendu Adhikari (leader of the Opposition) had said that something would happen on December 12. Was he speaking about this development?” The Association for the Protection of Democratic Rights (APDR) has decided to submit a petition at the CBI’s Nizam Palace office on Tuesday demanding a probe and punishment for any officer involved in the custody death.

“We want the officer in charge of the CBI camp office suspended. We demand compensation (for Sheikh’s family) and punishment for those involved,” the APDR’s Birbhum secretary, Sailen Mishra, said.