Melbourne Crime Investigation Unit detectives are appealing for information following a serious assault in Melbourne's CBD in December.
It is understood three men were sitting in Bourke Street when they were approached by an unknown male about 12.50am on Saturday 14 December last year.
The unknown male began assaulting a member of the group, when he was joined by three associates who also assaulted the group in an unprovoked attack.
A 19-year-old Keilor man sustained serious facial injuries which required surgery and ongoing treatment.
A 20-year-old Castlemaine man sustained non-life-threatening injuries and was taken to hospital.
The other victim, a 20-year-old man from the Romsey area, was also taken to hospital with non-life-threatening injuries.
Police were told the four offenders, believed to be aged in their mid-to-late 20's, fled the scene on foot.
Detectives have made extensive enquiries following the incident, but the four offenders remain outstanding.
Investigators have released images and of four males they believe may be able to assist with their enquiries.
The first offender is perceived to be Caucasian in appearance, with a medium build, brown scruffy hair and unshaven.
He was wearing a black cap, khaki unbuttoned shirt, a white top, blue jeans and white shoes.
The second male is described as having a tanned complexion, a slim build, with wavy hair tied back in a bun.
He was wearing sunglasses on his head, a white shirt with a black pattern, light pants and black shoes.
The third offender is described as having a tanned complexion and a slim build, wearing a white t-shirt, black pants, black and white Nike shoes.
The last male is perceived to be Caucasian in appearance and an average build, wearing a pink cap, a white striped shirt, light pants and grey and white Nike shoes.
Anyone who witnessed the incident, has dashcam/CCTV footage of the riders in the area or information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au
