Transit police are appealing for public assistance after a man exposed himself to a woman on a train on 16 August, Victoria Police say.
Investigators have been told a woman was on the Sunbury-bound train when a man sat near her and began masturbating in front of her about 9am.
The 20-year-old Narre Warren woman exited the train at St Albans Railway Station.
She was not physically injured.
It is believed the man exited the train at Sunbury Railway Station a short time later.
He is described as Caucasian in appearance and about 180cm tall with a medium build.
He had short balding brown hair and was wearing a black baseball cap with a white "New York" motif on the front, tan-coloured pants and black shoes.
Police have released images of a man who they believe may be able to assist with their enquiries.
Anyone with information is urged to contact Crime Stoppers.
