Marcus, 31, whose passion is trains and exploring the rail network, was the victim of a vicious unprovoked attack when he got on a Lilydale train at Ringwood about 7.30am on September 23.
The man allegedly suddenly yelled at Marcus, “Get off the f—— train”, before Marcus responded, “Stay away from me”.
The alleged attacker then told Marcus to shut up and threw him from his seat to the train floor.
He allegedly punched and kicked Marcus as he lay on the ground, before throwing him off the train when it arrived at Ringwood East station.
Marcus, who suffered bruising and significant mental stress because of the attack, caught a train back to Ringwood station, where he sought help from staff members.
Detective Leading Senior Constable Christopher Swiergon described the attacker’s actions as “absolutely horrendous conduct”.
“Everybody has the right to be safe on public transport”, he said.
Marcus’ mother, Elizabeth, said she had spent 20 years working to make sure he was safe and confident taking public transport.
Elizabeth said the attack on Marcus had also traumatised other parents who had children living with autism.
After the incident, the attacker got off the train at Lilydale station and rode away on his bike.
Police believe he had travelled from Prahran to Ringwood before getting on the same train as Marcus.
Police have released CCTV footage of a man they want to speak to over the attack.
He is described as being of Caucasian appearance, in his mid-30s, and as having a bald head.
He was wearing a black cap with a white motif, black jumper, black puffer vest, black tracksuit pants and black runners.
He was riding a dark-coloured mountain bike.
Anyone with information that can assist investigators is urged to contact police.