The residents of the four-storey building in Vidyasagar Colony that crumbled on Tuesday as efforts were being made to “lift” the building with a hydraulic jack, had hired the construction company for the job after seeing an online advertisement but without any verification, police said on Wednesday.

The police said they found the persons who were engaged in the process of “lifting” the building were former employees of a Haryana-based company with whom the contract was signed.

“Preliminary inquiry into the matter revealed that none of the flat owners is fully aware of the background of the men who they had hired for the work. They said they came across an online advertisement and contacted the men over the phone,” said an officer on the probe team.

The families neither visited their registered address nor did a background check, cops said.

“They (the families) relied upon the men whom they spoke to over the phone and later learned that they were former employees of a construction company based in Haryana. However, the contract was apparently signed with the company itself,” said the officer.

The police said they were verifying the alleged role of the Haryana-based company.

The developer of the building, Subhas Roy, was yet to be traced till late on Wednesday.

Roy’s last phone tower location was in West Burdwan district’s Burnpur, sources said.

His phone was switched off when Metro tried to contact him on Wednesday.

The police said the men who were directly involved in the repairs have been missing since the collapse.

The flat owners of the building have prepared a list of valuables that are inside the precariously tilted structure.

Officers of the local Netajinagar police station have made additional security arrangements outside the building to prevent possible theft.

Families who had purchased flats in the building have been living in rented apartments since the middle of December to facilitate the repairs. Now, they said, they are clueless about how their homes would be restored.

Although all the flat owners have been named as accused in the FIR lodged by the Kolkata Municipal Corporation, the police have not taken any immediate action against them on humanitarian grounds, sources said.

The building had crumbled moments after a hydraulic jack was used to “lift” one corner of the structure, apparently to level it with the rest.