Accused Bourke Street killer Dimitrious Gargasoulas was suffering from schizophrenia in the weeks before he allegedly drove into dozens of pedestrians, a court has heard.

But a hearing to determine whether he is fit to stand trial on allegations he murdered six people last year won't be held for three months, in a delay that has further frustrated a Supreme Court judge who is waiting on expert medical opinions.

Alleged Bourke Street killer Dimitrious "Jimmy" Gargasoulas

"That is unsatisfactory," Justice Lex Lasry said when told the prosecution's medical experts were waiting to assess Mr Gargasoulas and were still working through the medical material provided by the defence.

"This matter has got to proceed,” he said. “In May of this year it will be 17 months since the incident occurred."