Police are searching for a man who touched himself inappropriately on a London Underground train between Embankment and Kennington.
The incident occurred on the evening of Thursday 17 April, onboard a southbound Northern line train on the Charing Cross branch.
Detective Constable Allan McTaggart, of British Transport Police's sexual offences unit, said: "At about 8pm a passenger boarded the last carriage of the train at Embankment.
"After the train departed, they noticed a man sat close by had his hand down his trousers and appeared to be touching himself inappropriately. The behaviour continued for several minutes and only stopped when the man got off the train at Waterloo and boarded a Morden-bound train."
Officers are viewing CCTV footage from onboard trains and at stations, and have now released a photograph of a man they want to trace.
DC McTaggart added: "Who is the man in the suit? We want to speak to him as we believe he may have important information about what happened.
"People rightly expect to use public transport without being exposed to inappropriate sexual behaviour of any kind. We will always investigate all incidents reported to us."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference T/B5 of 15/05/2015.
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