UK Transport Police are appealing for witnesses after the incident on the 8:32 p.m. service from Edinburgh Waverley on Friday 22 October.
A woman on this train noticed that a man was staring at her and waving to her.
He then sat down next to her and started making sexual remarks to her before sexually assaulting her.
The man is described as a black or medium-sized man, standing about 6 feet tall and with a scar above his eyebrow.
He was wearing a navy Moncler jacket, black jeans, and blue and white sneakers.
Witnesses, or anyone with information, can contact the UK Transport Police by texting them to 61016.
You can therefore call them all on 0800 40 50 40 by quoting the reference 705 of 10/22/21.
Alternatively, you can call Crimestoppers anonymously on 0800 555 111.
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