The burglar alarm installed at the HDFC Bank's Shimpoli branch had never been checked.
Had it been, the Rs 27.5-lakh robbery on Monday may have been averted, because one of the bank staffers pressed the alarm twice while the robbers were in action.
However, the alarm was not working and did not buzz.
"The staffer took the risk of setting off the alarm thinking that it would alert people. Had the alarm been inspected earlier, the robbery could have been stopped," a police official said, requesting anonymity.
"The alarm was dysfunctional," confirmed Bhagwan Chate, senior police inspector, Borivli police station.
The police station is located not far from the bank. The alarm, in working condition, would have alerted the police's north region control room in Kandivli (E), which has all the required details, including the name and location of the bank.
The control room would have contacted the nearest police station and the police could have reached the spot within minutes. "We could have caught the five robbers," the official said.
Investigations are on and the police are not ruling out the possibility that an insider may have been involved.
The police also suspect that at least one of the robbers had done a recce of the bank premises before the robbery.
The CCTVs installed inside the bank have captured the images of the incident. It shows five armed men in raincoats and jeans, four of whom are wearing masks.
One of the robbers who was not wearing a mask can be clearly identified, officials said. The police have recorded statements of the bank employees based on which they will prepare sketches of the accused.