Transit Crime Investigation Unit is appealing for public assistance to identify a man after he showed pornography to a 10-year-old child.
Investigators have been told the man asked the boy to sit next to him on a Melbourne bound train before showing the young boy pornographic images on his phone on 24 January.
The incident happened between Sandown Station and Oakleigh Station about 11.20am.
It is believed the man boarded at Dandenong Railway station.
The offender was wearing a blue cap, blue short sleeved shirt, blue jeans and runners.
The man is perceived to be of Asian appearance and aged in his 50s.
Detectives have released an image of a man they believe may be able to assist with their enquiries.
Anyone who recognises this man or who may have witnessed this incident is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au.