A man touched himself on a Merseyrail train as it travelled from Liverpool to Formby.
Police were made aware of the incident just before 10pm, on December 21, 2022. Officers have now published an image of a man who may have information which could help their investigation.
A spokesperson for British Transport Police said: "Do you recognise this man? Officers investigating an incident during which a man committed a sex act on-board a train in Merseyside are releasing this image in connection.
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"At just before 10pm on 21 December 2022, a man was seen to commit a sex act as the service travelled between Formby and Liverpool. Officers believe the man in the image may have information which could help their investigation.
"If you recognise him, or have any information, please contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 554 of 21 December. Alternatively, you can call Crimestoppers anonymously on 0800 555 111."
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