Transit Crime Investigation Unit detectives are appealing for public assistance following a sexual assault in Reservoir earlier this month.
Investigators have been told the male offender approached the male victim at the Regent Railway Station at about 4.50pm on Monday 2 November.
The offender made an explicit comment towards the victim before sexually assaulting him.
Investigators have released CCTV footage and photos of a man they believe can assist with their enquiries.
The person is perceived to be Caucasian in appearance, about 50-years-old, with short grey hair and a thin build.
He was wearing a white facemask, dark coloured pants, a grey tee shirt, a grey jacket, black leather shoes, carrying a mobile phone and had a band-aid on his forehead.
Anyone with information is asked to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppers.com.au