BTP officers are appealing for further information following a report of upskirting on a train from Glasgow.
The incident happened between 9.50pm and 10.05pm between Glasgow Central and Clarkston stations on Saturday 9 February.
A man is reported to have used his phone to take pictures of a woman as she stood in the aisle of the train.
A passenger alerted the victim to the offence who then challenged the suspect.
The suspect left the train at Clarkston station; however officers believe he originally intended to travel to the East Kilbride area.
The man is described as white, aged between 40 and 50 years old, of average build and wearing a light coloured baseball cap, a khaki green jacket, a green scarf and blue jeans.
Officers would like to speak to anyone who witnessed the offence, especially the female passenger who alerted the victim.
Please contact BTP by texting 61016 or calling 0800 40 50 40, quoting reference number 727 of 09/02/2019.