Detectives from Transit Crime Investigation Unit are investigating after two people were assaulted on a bus in Braybrook on 15 July.
Investigators have been told both incidents occurred on the Number 408 bus which had left a Maribyrnong shopping centre and was en-route to Maidstone.
During the first incident, a 20-year-old man from Sunshine was verbally abused before being hit to the back of the neck with an unknown weapon at about 1.20pm.
The victim left the bus and the offender remained on board.
A short time later at about 1.30pm the second victim, who uses a wheelchair, boarded the bus and was subsequently verbally abused then assaulted by the same offender with an unknown weapon.
Both victims received minor injuries.
The offender was ejected from the bus on Churchill Avenue, Braybrook in the vicinity of the Braybrook Community Hub.
He is perceived as Caucasian in appearance and aged 30 to 40 years old with a slim build and sores on his face.
He was wearing a dark blue over coat with a small round orange logo in the upper left chest area, along with a hooded camouflage style top under the coat, dark-coloured peaked cap, dark pants, and black shoes with white soles and white stripes up the sides.
The offender also had a green back pack, and possibly had a light blue-coloured shopping bag.
Investigators have released images of a person who they believe might be able to assist police with their enquiries.
Detectives are appealing to the public who may have been on the 408 bus route between 9.10am and 1.30pm on this day and who may have witnessed or been involved in these incidents to come forward.
Anyone with information or who may have witnessed the incident is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au