The flash on a smartphone was a 27-year-old Hong Kong man’s undoing as he took pictures of a woman’s underwear on an escalator near Wong Tai Sin Bus Terminus on Monday evening.

At about 10pm, the 27-year-old woman was wearing a white knee-length skirt and was walking with her husband on Ching Tak Street.

Police arrested the man surnamed Lau, who tried to take pictures of the women’s underwear with his mobile phone, but forgot to turn off the flash, Apple Daily reported, citing a witness.

The woman cried for help and her husband called the police.

Lau was subdued by four male passers-by, who stopped him from deleting the pictures in his phone, Oriental Daily reported.