The case of a man charged with murder in Quebec's 2012 election shooting was delayed yet again Thursday after his lawyer said he wants his client to undergo another psychiatric evaluation.

Superior Court Justice Guy Cournoyer postponed jury selection in Richard Henry Bain's first-degree murder trial until May 2016.

Defence lawyer Alan Guttman said he has not yet been able to find anyone to conduct a new psychiatric evaluation of Bain.

He said he needs it so he can argue his client was not criminally responsible for his actions on the night of the shooting.

"You're dealing with a person who's (now) 64 years old, worked all his life, is a productive member of society, then all of the sudden this tragedy happens," Guttman said outside the courtroom. "There are questions that have to be asked."

Shortly before the shooting, Bain had been taking an anti-depressant that has side-effects including personality changes and hallucinations, the lawyer said.

Bain is charged in the slaying of lighting technician Denis Blanchette outside a Montreal nightclub on Sept. 4, 2012, as then-Parti Quebecois leader Pauline Marois was toasting her party's election win.

He also faces two counts of attempted murder and several weapons-related charges.

The trial was supposed to start in September, but jury selection is now set to take place May 24, 2016. Evidence presentation will begin a week later.

The prosecution has said it will take about six weeks to present its case.

Guttman said the postponement would allow him to find a psychiatrist who is familiar with pharmaceuticals.

He told the judge he was dissatisfied with a prior court-ordered psychiatric assessment, but said thus far he has been unable to find someone willing or available to conduct a new evaluation.

"There are a lot of professionals that would prefer not be involved for various reasons," he said.

Prosecutor Dennis Galiatsatos argued against the motion to postpone the case, which has already been subject to several delays.

He said there is a risk memories could fade over time.

"If you ask someone to remember what happened three years ago versus five or six years ago, things can be forgotten, details can be lost," Galiatsatos said outside the courtroom.

"I'm not saying that's the case with our witnesses, but it's certainly a concern that I had."

He also suggested the delays have made victims waiting for closure feel "disenfranchised."

"I'm sure you understand a lot of them are having a lot of trouble understanding, accepting what's going on," he said.

In his decision, Cournoyer acknowledged the prosecution's concerns, but said it was preferable to grant a delay than to risk a guilty verdict being overturned on appeal.

Another outstanding issue to be resolved before the trial is whether Guttman will be paid for his services.

He said his fee was supposed to come from the proceeds of the sale of one of Bain's properties, but that the buyer has not yet paid.

A pre-trial hearing to discuss the issue will be held Sept. 10.