Police have summoned the four brothers of Calcutta-based banker Shashi Prasad, who has emerged as the suspect in the double murder of his wife and four-year-old son inside their rented flat at a residential complex in the steel city last week.

An officer revealed that they had summoned Prasad's four brothers from his native village in Bihar to gather information about the 45-year-old Indian Overseas Bank employee's family background amid revelations that he often mistreated his wife Manju (41) of 17 years and that the couple's son Dweej was adopted.

Manju and Dweej were found dead with their throats slit on a bed in the first floor flat at Madhusudan Complex in Mango on Wednesday evening. Prasad reached the city from Calcutta in the small hours of Thursday.

"We are yet to get any strong evidence to proceed in the case and book Prasad. So, we have called his brothers from Bihar so that we can interrogate them. We expect them to reveal some vital information about his marriage to Manju and whether the couple's son was indeed adopted," said the police officer on condition of anonymity.

Deputy superintendent of police, Patamda, Ajay Thakur said they expected a breakthrough soon. "Nothing more can be said at the moment as it will hamper investigations," he added.

Prasad, barred by police from visiting Bihar Sharif in Bihar to perform the shraddh of Manju and Dweej, is staying at a hotel, having kept his rented flat under lock and key.

Residents of the apartment, KrittivasBhavan, have beefed up security after a meeting. While the open space at the entrance towards the apartment where the murder took place has been sealed with an iron barricade, security guards have been instructed to maintain records of visitors round the clock.

"We will ensure that no one enters our apartment without getting his or her name recorded at the entrance, where a security guard is posted round the clock," a resident told The Telegraph .

Residents are mulling separate CCTV cameras for all the 12 apartments in the complex.