A man who laughed after beating a homeless man to death in an unprovoked and “brutal” attack in Melbourne’s south-east has been jailed for 20 years.

Robert John Marshall, 22, had been drinking with friends at a park in Dandenong in November 2014 when he attacked Christian Williams.

The court heard Marshall demanded the 43-year-old’s wallet and phone before fatally bashing him.

Williams, who was intellectually disabled, never fought back.

Instead he began crying and asked Marshall “what did I do?”.

Marshall replied by repeatedly punching him in the face until he became unconscious.

He then dragged Mr Williams’ body around and when a friend told him “Look bro, look what you’ve done, you killed him”, Marshall laughed and said “I don’t care”.

He stomped on the man’s body, leaving an imprint of his shoes.

In sentencing Marshall, Justice Karin Emerton described the attack as brutal and protracted.

“Mr Williams was vulnerable and defenceless,” she said.

“Yours is a truly shocking crime; brutal and contemptuous. Your conduct can only be described as sickening.”

Killer in and out of juvenile detention

Mr Williams had an intellectual disability and had been living on the streets.

He had a young son which he remained close to and would walk to and from school each day.

The court heard the boy had “felt his father’s loss profoundly”.

The victim’s sister, Mandy Stevens, said the crime was sickening.

“It was disgusting what he did and I’m surprised he was even out on the street in the first place given his criminal background,” she said.

The court was told Marshall was in and out of juvenile detention since the age of 13 with his offending becoming more violent in his late teens.

Ms Stevens said more money needed to be invested in programs for young offenders.

“There were so many red flags. Why wasn’t something done years ago?” she said.

“Why was he out on the streets free to bash and kill people?”

Marshall will be eligible for parole in 16 years.