Santosh Thapa, the main accused in last month's murder of Congress leader Shanbabu Mukhi in Adityapur, surrendered before the chief judicial magistrate of Seraikela on Tuesday and was remanded in police custody for five days.

Thapa's interrogation is likely to tighten the noose around an influential businessman in Jamshedpur and his doctor brother for their alleged role in the conspiracy.

Adityapur thana OC Arvind Kumar said they had been making frantic efforts to bring in Thapa ever since his name figured in the Shanbabu murder. "We had carried out raids in Calcutta, Patna, Gaya and various cities of Uttar Pradesh, and had even sought a court order for property attachment. He finally surrendered in court around 12.30pm."

Shanbabu (50), a land broker from Dhirajganj, was shot dead during his evening walk on Adityapur Toll Bridge on June 15. On the basis of the complaint lodged by widow Ritika Mukhi, the police had filed a case of murder and conspiracy against nine persons, including Thapa, hotelier-cum-builder Prabhakar Singh and his brother Dr Dibakar Singh.

Six persons have already been arrested in the case so far. Police recovered a 7.65mm pistol from Chhotu Ram, one of the arrested sextet, who confessed to have shot Shanbabu dead.

"We will try to know whether the businessman and his brother were behind the murder. Once Thapa confirms Chhotu's allegations about the duo, we will arrest them," OC Kumar said.

Sources said Thapa (35), also a resident of Dhirajganj, had been pressuring Shanbabu not to create any hurdle for Prabhakar Singh who was apparently planning to purchase a plot. Later, Thapa plotted the murder and deployed two gangs on two sides of Adityapur Toll Bridge.

The gang on the Adityapur-end succeeded in its mission, while the others on the Kadma-end fled the scene. But, before absconding, they passed their guns - a 7.65mm pistol and a countrymade pistol - to one Rakesh Kumar who gave it to an aide who in turn entrusted a student of Dayanand Public School with the firearms.

On June 27, the Class XI student accidentally shot at and wounded a fellow student, Sudhanshu Gupta (17), while toying with the 7.65mm gun in classroom.