A teenager was indecently assaulted by a man between Brighton and Lewes after she fell asleep on an early morning train.
Detectives from British Transport Police have issued the CCTV image of a man officers would like to speak to.
The incident happened shortly after 7am on Sunday, 20 April, as the victim, an 18-year-old woman, travelled towards Eastbourne.
DC Vanessa Cottington said: “The woman initially struck up a conversation with a man sitting opposite her on the train.
“As the journey continued the woman fell asleep, but woke up to find a man touching her inappropriately.
“She immediately moved seats and continued the journey to Lewes, where both she and the offender boarded a replacement bus service to Eastbourne.
“The offender left the bus at Polegate and was seen to board a train to Eastbourne.”
Following the incident detectives have carried out a number of enquiries and, as a result, have managed to isolate the image of a man they believe has key information about the incident.
DC Cottington added: “I am convinced the man will be able to help our enquiries and I am calling on anyone who recognises him to get in touch. I would also like to hear from anyone else who may have information about the incident.
“Incidents of this nature are relatively rare on the rail network, but, when they do happen, can be extremely upsetting for victims.
“We work closely with the train companies and local police forces to trace offenders and, where appropriate, put them before the courts, but we do need the public to help.”
If you recognise the man, or have information about the incident, please call British Transport Police on 0800 40 50 40 or ring Crimestoppers, anonymously, on 0800 555 111. In all calls please quote log SSUB/B5 of 29/4/14.