House-owner Avijit Ghosh points to the empty jewellery boxes that the robbers left behind after the theft on Sunday night. Picture by Pradip Sanyal

A gang entered a Salt Lake house after managing to get hold of the key and decamped with cash and jewellery worth Rs18 lakh on Sunday night.

All the while, the three occupants of the BB block house were asleep. They came to know about the theft only on Monday morning.

“We went to bed a little early on Sunday. We were in the rear room and had no clue about what was happening in the rest of the house,” said owner Avijit Ghosh, who works for a central government undertaking.

He lives with wife Aparna and their daughter Arinita, a Class XI student, on the ground floor. The first floor of the building has been rented out.

Police have come to know after a preliminary probe that the thieves entered the house after breaking open a small lock on the collapsible gate.

“They were confronted with another locked door, the key to which was kept beside a closed window. The thieves took the key after breaking open the window and opened the door,” said an officer of Bidhannagar (North) police station.

“Once inside, they entered the room where the safe is kept. The thieves took the key from a drawer in the room, opened the safe and cleaned out the cash and the valuables,” the officer added.

Ghosh ruled out the involvement of their maid, an aged widow, in the theft but the police are not sure. “It seems the gang knew where the keys to the main door and the safe were kept. Someone who knew about the family could have supplied the information to the gang,” said the officer.

Ghosh told the police that for the past month, he had spotted an unknown person taking a stroll in front of their house in the evening.

“We are investigating the matter,” said Supratim Sarkar, the superintendent of North 24-Parganas police.