A key accused in the Madhyamgram twin killings was arrested late on Monday, taking the number of suspects behind bars for the murder of promoter Babu Sen and one of his associates to eight.

Babu Ghosh, believed to be one of the conspirators, has been picked up from an apartment in Lake Town's Boat Club area.

Among those behind bars is a developer named Babu Mondal, who the police claimed was Sen's business rival and the principal conspirator.

Police said Ghosh had admitted during questioning that he had received around Rs 50,000 from Mondal for gunning down Sen.

A part of the amount was allegedly used to hire criminals, a cop quoted Ghosh as saying in custody.

A group of about 15 men on motorcycles and in a Sumo had on May 7 evening waylaid Sen, who was travelling in a car with his aides Nitai Pal, alias Nungkai, and Abhijeet Guha, on a crowded stretch of the road that connects Madhyamgram Chowrasta on Jessore Road with Madhyamgram station.

The gang sprayed bullets on Sen's Alto 800. While Sen and Nungkai died in the shooting, Guha survived. The driver, Jagadish, escaped unhurt.

Sen, who was also involved in landfill business across Barasat and along Kalyani Expressway in Sodepur, was returning from a meeting allegedly organised by Ghosh to resolve business disputes.

Ghosh fled to Digha after the shooting and thereafter kept changing base, the police said.

"Babu Ghosh left behind his mobile phone and kept travelling on buses to various locations," said Bhaskar Mukherjee, the additional superintendent of police, North 24-Parganas.

Sources said that from from Digha, Ghosh had fled to his in-laws' house at Bongaon in North 24-Parganas, from where he went to Baduria in the same district.

On May 11, the police had raided a suspected hideout in Baduria but failed to find Ghosh.

"From Baduria, Ghosh returned to Bongaon before taking a bus to Berhampur on his way to Siliguri. From Siliguri, he went to Gangtok," an officer working on the case said.

"Babu had spent May 10 to 18 travelling on buses. He never checked in at a hotel for fear of getting caught. He returned to Calcutta a few days back to collect money."

Last Saturday, Ghosh had allegedly visited his in-laws' house after running out of money. But all members of the family, including Ghosh, allegedly left before the police reached the spot.

"None of his acquaintances had given him shelter but one of them arranged money for him through a promoter in Lake Town. He was arrested when he went to Lake Town to collect the money," a police officer said.

The police had set up several teams that scanned the financial transactions and mobile communications of people known to both Ghosh and Mondal, who was seen in transport minister Madan Mitra's company.

"Ghosh helped Mondal in his realty business and also in filling up ponds in Belghoria and Kamarhati," the officer said. "He had built a network with a section of criminals operating in and around Barasat and Madhyamgram."