A family returned home to Collin Lane, in central Calcutta, on Wednesday night to find the main door ajar. Jewellery and other valuables and cash were missing.

“A CCTV camera installed in front of a guest house in the neighbourhood captured two thieves unlocking the door of the house with a key. One of the thieves was Ahmed Khan, 45, a next-door neighbour of the family,” an officer of Park Street police station said.

Khan, a taxi driver by profession, was arrested at his house early on Saturday. “The entire booty except the cash was recovered from his home,” the officer said.

The police are looking for his alleged accomplice, who lives near Park Circus.

“What is still not clear is how the thieves made the duplicate key to the house,” the officer said.

Mohammad Shahid and his family had stepped out around 5pm on Wednesday and returned at 11pm.

In his complaint, Shahid mentioned that they found the main door of the house ajar when they returned.

“There were no marks of forced entry but the door was open,” the officer said.

Stepping in, the family discovered that cash and jewellery and other valuables had been stolen from the cupboard. The cupboard was locked but the key was hanging from a door handle.

The family had initially tried to investigate the matter by themselves.

Having failed to zero in on any suspect, they approached Park Street police station on Friday.

The house is located in the middle of a crowded neighbourhood in Collin Lane, a few hundred metres from Park Street. “No one saw any suspicious activity around the house on the day of the incident,” the officer said.

“We were sure that the thieves had entered when the family was away, between 5am and 11pm,” he said.

The investigators found a CCTV camera installed on a guest house next to Shahid’s house. Sources said the camera footage showed two men, one of whom lived opposite Shahid’s house, unlock the door and enter the house that day. They left the premises with bags.