Detectives need to identify this man (Credit: BTP)
The man walked down the aisle of the c2c service and sat near the victim shortly before 9pm on Monday, 18 July.
He exposed himself and masturbated while looking at the victim, who then got up and moved away from the man.
Detectives have released CCTV images of a man who may information which could help with their investigation.
Anyone who can help them identify and locate him should contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 619 of 18 July.
Alternatively, you can call Crimestoppers on 0800 555 111.
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