British Transport Police have released an image of a man they would like to speak to after a woman was sexually assaulted while she slept on a train.
The incident is said to have happened on the 11.12pm service from Waterloo to Basingstoke on November 22, 2012.
Officers would like to identify and speak to a man who they believe may have key information.
The man was believed to have got off at Surbiton station.
Detective Constable Andy Parkinson said: "The victim, a 23-year-old woman from Surrey, was travelling. During the journey she fell asleep and awoke to find a man was touching her indecently.
“Shocked at the man’s actions, the woman confronted him before moving to another part of the carriage.
"The man’s behaviour was unacceptable and has understandably left the victim feeling shocked and shaken.
“I would urge anyone who recognises the man pictured, or knows his whereabouts, to contact us."
Anyone with information should call British Transport Police on 0800 40 50 40 quoting B5/LSA of 09/01/2013 or contact Crimestoppers anonymously on 0800 555 111.