The tin-roofed house from where a tunnel was dug to break into the Sonali Bank vault may have been rented out solely for the burglary purpose.
The two-room house was given to one Sohel two years ago, but it bore no vestiges of daily living. Instead, it is full with earth removed to make the underground passage.
Police yesterday detained the owner of the house for interrogation.
Meanwhile, police have no lead to catch the robbers yet, a whole day after the discovery of the bank robbery. The burglars had made off with Tk 16.4 crore.
CID Inspector Md Shahjahan said, "We found a used cap and a mask from which we will be able to trace out DNA profiles of the robbers. We also found some cloths, spades, electric wires, electric saw blades etc."
The robbery took place at the bank's main branch in Kishoreganj located on Isa Khan Road, Rathkhola.
Anwar Hossain Khan, superintendent of Kishoreganj police, said: "We have found that while renting the house Sohel had told the house owner that he was there for work. He never specified what sort of work though.”
Sonali Bank Managing Director Prodip Kumer Dutta told The Daily Star that breaking into the vault was not an easy task, and it was possible the person who conducted the robbery was a skilled operator.
In Sohel's room, police found bamboo staffs used to reinforce the walls of the tunnel to make sure it did not cave in.
The discovery of the robbery was first made on Sunday when bank staff entering the vault found the money gone and a hole in the floor. Join Custodian (cash) Mohsinul Haq and Joint Custodian General Hasan Ahmed Moin were the first to notice it.
"The money was on a table," they said.
However, neither was able to say why the money was kept on the table instead of securely inside the iron safes.
Twelve bank officers, including the manager of the branch and four neighbours, were also taken in for questioning yesterday.
Eight policemen stationed in the bank have temporarily been suspended for negligence in duty on Sunday night.
Meanwhile, the Bangladesh Bank (BB) yesterday instructed all schedule banks to improve their vault security.
All schedule banks must set up security tested doors with fencing steel walls around the vaults, said the central bank said in a statement.
The BB directed the banks to install CCTVs inside the vaults and ensure security alarm round the clock. They have been also asked to bring everything in a vault under insurance coverage.