Transit Crime Investigation Unit detectives are appealing for information after a man performed an explicit sexual act on a train from Geelong last month.
Investigators have been told a man boarded a Melbourne-bound train at Lara Railway Station about 10.10pm on Monday, March 7.
He sat next to a 29-year-old woman and performed a sexual act before getting off the train at Southern Cross Railway Station.
Detectives have released images of a man they believe may be able to assist with their enquiries.
The man is perceived to be Caucasian in appearance, with a slim build and short fair hair.
He was wearing Sydney Swans AFL cap, grey zip up hooded jumper, black shorts and dark grey runners.
Anyone who recognises the man or has information regarding the incident is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at crimestoppersvic.com.au.