Transit Crime Investigation Unit detectives are appealing for public assistance after a man performed a lewd act in Bulleen.
Police have been told the man engaged in the lewd act in the presence of young woman on the route 905 bus about 5.30pm on September 14.
The man departed the bus at the Bulleen terminus on the corner of Thompson and Manningham Rds.
The woman was not physically injured.
Investigators have released video footage and images of a man they believe may be able to assist with their enquiries.
He is described as Caucasian, in his early 20s with short brown hair and brown eyes.
He was wearing a beige jacket with a black hoodie underneath and black pants.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.
com.au