About 15 documents related to the building were obtained from the building's owner Manish Lakra and brothers Vijay and Harish Goel, said Deputy Commissioner of Police (Outer) Sameer Sharma. The Goel brothers had rented two floors in the building to run their CCTV camera and router manufacturing and assembling company. The fire is suspected to have started in their office. The three have been arrested.

Sharma said, "We have sent letters to more then 10 agencies, including Delhi Jal Board and BSES among others, to get more documents and details related to the company and building to also ascertain if any fake fire NOC was obtained by them."

He said that during investigation, it has emerged that there was a change-over switchboard for electricity connection on the first floor of the building where cardboards and other materials were dumped which may have caused the fire to spread quickly. But, the picture will become clear after the forensic reports are received.

Sharma added, “After a preliminary inquiry, it was found that the building was congested due to storage of CCTV cameras and routers, workstations, and offices. Steel sheets were used to separate the staircase from floors and partitions inside the building were used for storage."

Police have recovered 27 bodies from the building. As of Sunday, 14 of them had been identified as women and six as men. Nineteen people are still unaccounted for.

To ascertain the identity of the dead and trace those who are missing, police are trying to track the the location of their mobile phones, an official said.

The blood samples of the Goel brothers have also been taken as part of the investigation, he said.

Lakra was arrested from Ghevra Mod while he was en route to Haridwar in Uttarakhand on Sunday, two days after the incident. He was running a real estate business and also owned a shop on the ground floor of the building, police said, adding that his family members are yet to be traced.

Lakra used to live in a two-room-kitchen house with his mother, wife and two children on the fourth floor of the same building. They managed to escape to the adjacent building when the fire broke out, police had earlier said.

(With PTI inputs)