Detectives from the Transit Safety Division are investigating a sexual assault which occurred on a bus in Thornbury last year.
Investigators have been told a 24-year-old woman was on a bus in Thornbury when a man got on at Station Street around 1.15pm on 16 November 2018.
It is believed the man sat next to her and touched her inappropriately causing the woman to yell out.
The man moved seats and sat behind the victim before he disembarked shortly after near the corner of Dundas Street and Victoria Road.
The alleged offender is described as unshaven, Caucasian in appearance, aged between 40 and 50-years-old, with a heavy build and dark-brown hair.
He was wearing a blue-grey jumper and dark-coloured pants.
Investigators have released CCTV images of a man police believe may be able to assist with their enquiries.
Anyone who recognises this man or who may have witnessed this incident is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au