Four Melbourne medical experts agree accused Bourke St driver James "Dimitrious" Gargasoulas has schizophrenia, but only one of them believes he is fit to stand trial over the 2017 rampage that killed six people.
Gargasoulas is facing an investigation hearing before a jury in the Victorian Supreme Court to determine if he is fit to stand trial on six counts of murder and 28 charges of attempted murder.
Forensicare consultant psychiatrist Andrew Carroll on Thursday said the 28-year-old had expressed a desire to stand to trial over the 2017 Bourke St mall rampage so he could tell people he was the Messiah.
"He absolutely wanted to make sure he had a trial of some kind so that he has a public platform (for his Messianic beliefs) so the public can ask questions about why these events happened," Dr Carroll told the court.
"In his mind he believes that would lead to some kind of uprising and save the planet."
Dr Carroll is the third psychiatrist to tell the hearing that Gargasoulas suffers from schizophrenia and is unfit for trial.
Two other psychiatrists have previously told the court Gargasoulas believes he is "the Messiah".
Prosecutor Andrew Tinney SC said Gargasoulas' ability to discuss his court case implied he was capable of making a decision about whether to plead guilty or not guilty.
But Dr Carroll said Gargasoulas' reasoning was heavily influenced and compromised by his delusional beliefs about being the Messiah.
"His delusional beliefs are of such a nature that he is unable to rationalise the options that are open to him," the psychiatrist said.
"In my view this renders him unfit to stand trial."
Forensicare psychologist Michael Daffern believes Gargasoulas is fit to stand trial despite his schizophrenia.
"He does have these delusional beliefs and thoroughly believes he is the saviour," Professor Daffern said.
"I don't believe that these delusional beliefs are overwhelmingly undermining his capacity to make a logical decision in relation to a plea."
Prof Daffern also said Gargasoulas was not "malingering" or making up his psychotic illness.
The hearing before Justice Lex Lasry continues.