Kolkata, Dec 13 (IANS): Birbhum district police have launched a preliminary probe into the mysterious death of Lalan Sheikh, the prime accused in the Bogtui carnage case, in Central Bureau of Investigation (CBI) custody.

The victim's family has filed a first information report (FIR) at the local Rampurhat Police Station holding the CBI responsible for Sheikh's death. A case has been registered on the basis of the FIR and a preliminary investigation launched.

District police sources said that they are waiting for reports of the post-mortem which will be conducted in front of a judicial magistrate on Tuesday. In fact, Birbhum district police superintendent Nagendra Tripathi has already informed the media persons that the district police will carry out its own independent probe in the matter on the basis of the post-mortem report.

Meanwhile, CBI sleuths, as per norms, are preparing themselves to present their own explanations to the Calcutta High Court. Since the investigation is court monitored it has made it mandatory for the central agency to explain to the court on the reasons of mishap which happened in their custody.

Leaders of the ruling Trinamool Congress have already alleged some foul-play behind the mysterious death of Lalan Sheikh after a picture of his hanging body in the toilet of CBI's camp office went viral.

The body, sporting only a black underwear, was seen in a "partial hanging" position with the legs touching the floor of the toilet. In the picture it is seen that a gamcha (Indian town) is tied around his neck and also tied with the water-pipe on the toilet wall above his head.

CBI sources said that the instance of "partial hanging" in case of suicides is not a very uncommon factor and that in the past, there had been several instances where the legs of the person committing suicide by hanging himself touched the floors at a later stage.

However, according to sources, the development is bound to affect the investigation of the Bogtui carnage considering that Lala Sheikh was the key man leading the revenge-killing following the murder of local Trinamool Congress leader, Vadu Sheikh during the wee hours of March 21 this year.

Meanwhile, additional central armed forces have been deployed at CBI's Rampurhat camp office in Birbhum district, where the mishap took place, apprehending public backlash.