The family of a man brutally killed in the car park of a Melbourne shopping centre last week were so distressed they did not recognise his brother in CCTV footage captured at the scene, police say.

Key points: Police urge Jonathan Dick to come forward after brother's death

Police urge Jonathan Dick to come forward after brother's death Family did not think they knew person captured in CCTV

Family did not think they knew person captured in CCTV Investigators worried Dick could be "overwhelmed by situation"

The homicide squad are searching for the older brother of 36-year-old David Dick, who was killed at the Westfield Doncaster shopping centre on Friday, with his attacker leaving a bloody trail away from the crime scene.

A fitness group found David injured near a lift lobby just after 6:00am and called triple-0.

Police have previously said they believed the attack was targeted, and yesterday released CCTV footage of a man in the same area the day before the killing.

Jonathan Dick is believed to be headed towards NSW or Queensland. ( Supplied: Victoria Police )

Homicide squad detectives have now issued an appeal for the victim's 39-year-old brother, Jonathan Dick, to come forward.

David's family, including his mother Carol and brother Simon, made a plea for anyone with information to contact investigators, not realising it was Johnathan in the footage.

"We'd actually shown the family the footage before we did the media conference [on Tuesday], and I've had the question how would you not know that's your son," Detective Inspector Mick Hughes from the homicide squad said.

"This family is under so much stress.

"I spoke to Carol yesterday, I was with her for about an hour, and [uncle] John and Simon, and not one of them had an inkling that this could have even been a possibility.

"When we got the recent photo of Jonathan we thought, yeah, this is a possibility.

"This is a really open and honest family ... and not only did they think it wasn't their son and brother, they didn't think it was anyone they knew."

He said the mother, Carol Cloke, said the relationship between Jonathan and his siblings was good.

Jonathan Dick may be in QLD, NSW, police say

David Dick's family said he was in a happy place before his death. ( Supplied: Victoria Police )

Detective Inspector Hughes said Jonathan had been reported missing two days ago and police were concerned his safety as it may "be an overwhelming situation to him".

"We're saying don't do anything to hurt yourself, just remember you still have a family here regardless of the circumstance you may find yourself in."

He said Jonathan had recently been diagnosed with a mental health condition and had chosen not to take medication.

Detective Inspector Hughes said Jonathan, from Seymour in central Victoria, could be headed for New South Wales or Queensland

"He lost his dad about six months ago, [his] dad used to live in Queensland so it wasn't unusual for Jonathan to jump in his car and drive up and see his dad and not contact anyone," he said.

He could be driving one of two vehicles - a 1997 blue Ford Fairmont sedan with registration ONV-954, or a white 2002 Ford Falcon station wagon with registration RIL-435, police said.

"We're concerned for the public safety only from the point of view we ask them not to approach Jonathan," Detective Inspector Hughes said.

"There's no suggestion he'd been aggressive to anyone else and we still don't know the motive for this attack."

David Dick 'was in a happy place'

Yesterday, the victim's family said they did not understand why their son had been murdered so "viciously".

David and Jonathan Dick's family has been devastated by the events, police say. ( ABC News )

Ms Cloke said her son was getting his life together and was in a happy place before his death.

"He was the most magical person and we all loved him so much and he had enormous strength of character," Ms Cloke said.

"He was very happy and he's been really settled down for the last while now and getting on with his life."

The footage of the suspect released by police showed a man entering and exiting the lift where Mr Dick died, armed with a long object.

Police said they believed the man returned at the same time the following day, when Mr Dick was killed.