Police are looking for a man after a woman was assaulted on a train between London Bridge and Chislehurst.
British Transport Police (BTP) officers say the suspect followed the woman onto the 12.48am Charing Cross to Orpington service at London Bridge station on July 18.
The man is said to have sat next to the woman and "touched her inappropriately for around 20 minutes" before getting off.
Detective Constable Andy Parkinson said: “He sat next to her and began to touch her inappropriately for a period of around 20 minutes before he left the train at Chislehurst station.
“There were a few people on the train at the time who may have thought the pair were a couple and were reluctant to step in.
"This was not the case and I am urging these people to come forward as they may have information crucial to our investigation.”
Det Con Parkinson continued: “The man’s behaviour was totally unacceptable and inappropriate and we are currently following several lines of enquiry."
Other passengers were on the train at the time, officers say, but may not have stepped in because they thought the man and woman were together.
BTP released an image of a man they would like to speak to in connection with the incident today (Aug 18) and are calling for anyone with information to come forward.
Call 0800 40 50 40, or text 61016, quoting reference B8/SSUB of 15/08/2014. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111