Vic killer laughed after unprovoked murder

A Victorian murderer who laughed after killing an intellectually impaired man with his bare fists will be released from prison before he reaches the age of his victim when he died.

Robert John Marshall, 22, has been jailed for 20 years, with a minimum of 16, for beating vulnerable homeless man Christian Williams to death in an attack the judge branded as "sickening".

Mr Williams cried and asked Marshall, "What did I do?" as the younger man punched him repeatedly.

The victim was 43 but had the intellectual capacity of a 10-year-old as the result of being hit by a car as a child.

Relatives described him as "loyal, kind-hearted and trusting of everybody".

Victorian Supreme Court Justice Karin Emerton said Mr Williams was an "overgrown kid", who was a loving and reliable father to his son, Jack, in the sentencing hearing on Tuesday.

"He died pointlessly and tragically in terrifying circumstances," she said.

Mr Williams was listening to music and preparing to sleep on a sound stage in Victoria's Dandenong Park on November 18, 2014, when Marshall approached and demanded his wallet.

The Keysborough man was intoxicated, having spent the afternoon drinking cask wine with his friends in the park, and punched Mr Williams in the head.

Mr Williams fled, but Marshall caught up with him and punched him four more times.

He then dragged Mr Williams back onto the sound stage and continued to beat him - even after the 43-year-old lost consciousness.

One of Marshall's friends said, "Look bro, you've killed him".

Marshall laughed and replied, "I don't care", before stomping on Mr Williams.

Justice Emerton said the crime was brutal, unprovoked and protracted.

"Your conduct can only be described as sickening," she told Marshall, adding the fact that he was very drunk was not a mitigating factor.

"You showed a complete disregard for Mr Williams' humanity."

Mr Williams' relatives hugged after the sentence was handed down, but outside court his sister Mandy Stevens said Marshall shouldn't have been out on the streets given his criminal history.

"There were so many red flags," Ms Stevens told reporters.

"He'll still be younger than my brother when he gets out."