There wasn't anyone in the bank. Whoever this was, they had waited until after the bank was closed to break in. They had picked the lock too...the storm had provided them with cover and the power outage meant it was difficult to see...they were smart, whoever they were.
The door to the vaults was guarded with an electronic alarm-meaning when the power went out it had been disarmed, thus not alerting the authorities. The door had been blasted open-it looked like it had been struck by lightning