Detectives from Transit Crime Investigation Unit are investigating a sexual assault between Melbourne and Caulfield on 16 April.
Investigators have been told both the female victim and an unknown male boarded a rail replacement bus on Flinders Street near Federation Square and disembarked at Caulfield Railway Station about 6.25pm.
It's understood the man sat next to the woman on the bus and assaulted her during the trip.
The man is perceived to be of Indian sub-continental appearance, 175cm tall, a thin build with black hair.
He was wearing rectangular glasses with a black thick frame, black pants, a black or dark grey knitted cardigan and a black backpack.
Investigators are keen to speak to anyone who may have witnessed the incident or was travelling on the bus at the time.
Investigators have released Facefit images of a man they wish to speak to in relation to the incident.
Anyone with any information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au
