Transit police are hoping to identify a woman following an unlawful assault on a Sandringham bound train late last month.
Investigators have been told both the female victim and offender boarded the train at Flinders Street Railway Station and sat adjacent to each other shortly before 7.15pm on 27 June.
A short time into the journey, the offender approached and assaulted the victim for an unknown reason.
The offender then sat down again before the victim disembarked at the next station.
The victim, a 38-year-old Northcote woman, was not injured as a result of the incident.
Investigators have released a CCTV image of a woman they believe may be able to assist with their inquiries.
She is perceived to be Caucasian in appearance, about 160cm tall, with a medium build, fair complexion, a nose stud and peroxide blond hair.
Anyone who recognises the woman or with information is urged to contact Crime Stoppers on 1800 333 000 or submit confidential report online at www.crimestoppersvic.com.au