Inching closer to cracking the murder case of builder Shailesh Kumar Singh, police on Sunday said his assailants fled on motorcycles.

Patna senior superintendent of police (SSP) Manu Maharaj said police have zeroed in on the gang involved in the killing of the 42-year-old builder.

“We are close to unravelling the mystery behind the murder of Shailesh. We have gathered scientific evidence to establish the involvement of the assailants,” he said.

Officials associated with the investigation said the killers had parked their vehicles at a distance from the under-construction warehouse of Shailesh and they sped away on their motorcycles after committing the crime.

The SSP said members of the Special Police Team (SIT) are interrogating the victim’s driver, Sikandar, from time to time. Sikandar, who drove Shailesh to the site from his Frazer Road home, was not on the spot when assailants opened fire. The SIT, which has been assigned to probe the case, is learnt to have prepared a list of contract killers operating in and around the city.

The SSP refused to disclose the name of the gang because it could affect the investigation but hinted at the involvement of contract killers whose number might exceed to four or five. Preliminary investigation had suggested involvement of only three persons, who escaped on foot after executing the crime in daylight. Shailesh, the managing director of Kalindi Construction Private Limited, was shot dead by criminals when he had gone to oversee the construction work at his warehouse on June 26.

The victim’s wife, Anju, had accused her husband’s former business partner Rakesh Kumar’s widow, Sanrakshita, and one Dharmendra Pandey, of hatching the conspiracy. The police quizzed both suspects but did not arrest them. Sanrakshita had staked her claim on the 36 cottahs on which Shailesh was constructing his warehouse. She claimed that Shailesh had duped her after the murder of his business partner Rakesh few years ago.

An investigating officer, however, said the police did not take the named accused into custody immediately because they wanted to ascertain their role in the episode.

“The two are under surveillance of the investigating officers,” he added.