A man dying from a suspected sword slash to the throat was enough to capture the attention of the public - but the fact his family failed to recognise the alleged killer, his own brother, has added to the intrigue.

His mother Carol Cloke and brother Simon Dick bravely fronted media on Tuesday to beg for information that could lead to the killer of David Dick, 36.

They did so seemingly unaware the images that appeared behind them of a man police were hunting for was David and Simon's brother, Jonathan Dick.

David Dick's mother Carol Cloke with David's uncle John Hird (left) and his brother Simon Dick. Photo / News Corp Australia
David Dick's mother Carol Cloke with David's uncle John Hird (left) and his brother Simon Dick. Photo / News Corp Australia

Their reaction did not surprise one violent crime researcher.

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Samara McPhedran, senior research fellow of the Violence Research and Prevention Program, at Griffith University, told news.com.au the trauma of losing a family member to murder could have such a severe impact it altered the effects on their loved ones' own behaviour.

"The sudden loss of a loved one in violent circumstances is an incredibly traumatic experience for family members. The stresses associated with this type of loss can have substantial immediate, as well as long-term, impacts on many aspects of family members' lives," Dr McPhedran said.

That included emotional and psychological distress, but also extended to cognition and general behaviour - meaning it was more than possible they didn't recognise their own flesh and blood when shown the CCTV images by police.

Homicide squad detectives believe Jonathan Dick is the man shown in the footage at the Westfield Doncaster carrying what is thought to be sword.

Asked if the person in the footage released on Tuesday was Jonathan, Detective Inspector Mick Hughes said: "I'm working on that principle that it is, yes."

Hughes said it was an "unusual" circumstance, but he was not going to "second guess" why they failed to recognise him.

Jonathan Dick has lost a significant amount of weight and his hair is shorter and lighter as seen on the footage at Westfield.

"Not one of them had an inkling that this could have even been a possibility."

Police would like to speak to this man after the vicious murder of David Dick, inset.
Police would like to speak to this man after the vicious murder of David Dick, inset.

Hughes said the family was under huge stress but was "open and honest" to deal with, so police had no reason to disbelieve them when they were shown the footage and asked if they knew the person.

Soon after David Dick was found dying in the carpark lift at the Westfield, police believed it was a targeted attack and immediately began looking at those closest to him.

Officers looked at a recent picture of Jonathan and thought it was "a possibility" he was the man on the CCTV.

"But when you're speaking to the family ... These are a really honest, open family, when you talk to people like that you take them at what they're saying - that they don't know him. Not only they didn't think it was their son and brother they didn't think it was anyone they knew," Insp Hughes.

The shocking reality was tough for the family to digest. Cloke is said to be struggling with the news, while Simon Dick, who was close to his brothers, was feeling even more traumatised.

Police believe Jonathan, a plasterer, may now have fled to NSW where he has family members or even further away to Queensland, where his father lived until his death six months ago.

He had been living in the township of Seymour, north of Melbourne, and was recently diagnosed with a mental health disorder after several years of struggle.

His uncle reported him missing on Monday.

Victoria Police said on Thursday afternoon the investigation was ongoing, and declined to say if there had been any sightings of Jonathan Dick.