Victims' families of Melbourne's deadly Bourke Street rampage are devastated after a jury failed to find murder-accused James "Dimitrious" Gargasoulas mentally fit to stand trial.
Jurors were dismissed on Friday after being unable to agree unanimously whether the 28-year-old should stand trial.
It means a second fitness hearing is likely to be held with a new jury to determine if Gargasoulas is fit to stand trial on six counts of murder and 28 of attempted murder.
"The families of the loved ones killed in this tragedy are devastated by this further delay," Genna Angelowitsch from Adviceline Injury Lawyers said.
"They hope the process can quickly move forward from here."
The statement came from lawyers representing families of five victims: Zachary Bryant, Sydney woman Jess Mudie, Japanese man Yosuke Kanno, Bhavita Patel and Matthew Si.
Three-month-old Zachary was the youngest victim.
His dad spoke outside court after Friday's outcome.
"It's disappointing. That's all I'll say," Matthew Bryant said.
The Supreme Court investigation hearing was to determine if Gargasoulas is fit to face trial accused of running down pedestrians in January 2017, killing six people.
The jury of 12 deliberated for nearly four days after hearing expert evidence but they could not reach a unanimous decision and on Friday morning Justice Lex Lasry discharged them without a verdict.
"There are those among you who had strongly held views and you were right not to compromise," Justice Lasry told the jurors.
"It is unfortunate we have got to this stage as it means the matter has to run again."
Gargasoulas is accused of murdering six people, including two children, when he allegedly ploughed a car through pedestrians.
Justice Lasry said the fitness investigation would have to be repeated but suggested it could be unsuccessful a second time.
"Having heard all the evidence, firstly I am not surprised the jury struggled to reach a decision," he said.
Medical experts who testified in the case were divided over the question of Gargasoulas's fitness.
Two psychiatrists believe he is unfit for trial but one psychologist disagrees.
The defence argued Gargasoulas was "profoundly psychotic", believing he is the "messiah" sent to save the world from a comet, and should not stand trial.
But prosecutors said he should, arguing he understands his case and the trial process.
"(He) has the presence of mind to know that if it's his lot in life to be saving the world, he wants to be doing that from the relative comfort of Thomas Embling Hospital, rather than the 23-hour lockdown of prison," crown prosecutor Andrew Tinney SC said on Monday.
Friday is Justice Lasry's last day as a Supreme Court judge, as he must retire because of his age.
The Gargasoulas case will be handed to Justice Mark Weinberg and is due to return to court on July 23.