Kolkata: Suraj Kumar Sau, a security guard working at the Big Bazaar outlet in Kolkata's landmark Metropolitan Building in Chowringhee had planned his burglary meticulously, but a single mistake gave him away and he had to land behind bars.

On Wednesday night, Sau, who was posted at Gate No 1 which faces Chowringhee, left after work, but returned an hour later.

He entered the building through a secret passage from the rear of building on S N Banerjee Road to an unused wooden door, that opened to the store's first floor.

Sau had kept the door unlatched from inside during duty hours. After, he packed 204 cellphones, 20 tablets, 12 digital cameras, 143 sets of costume jewellery and two smaller trolleys into two large bags, he walked out at 2 am on Thursday, hours before dawn.

It was then that Sau committed an error. He had kept his face covered by towel to evade identification on Big Bazaar's outlet cameras, but when he came out of the building from the main gate, by using the emergency keys kept inside the store to lift the shutters of Gate No. 2, he took out the towel from his face, to hail a night taxi.