Melbourne Sexual Offences and Child Abuse Investigation Team detectives have released CCTV following a reported sexual assault at Federation Square in May.
The incident happened in toilets near the building off Flinders Street around 2pm on Wednesday, 5 May.
Investigators have been told that two 15-year-old girls were in the toilets when they were sexually assaulted by a man they had met earlier that day at a nearby fast-food restaurant on Swanston Street.
Detectives have released CCTV of a man who they believe can assist with their enquiries.
The man is perceived to be aged in his 20s about 185cm tall, with a beard and tattoo on his right arm.
Police are keen to speak to any witnesses that may have been at Federation Square around the time of the incident.
Anyone who recognises the man is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au.