FREDERICTON -- A Fredericton man accused of murdering four people in an August shooting spree is set to return to court Friday following a 60-day psychiatric assessment.

The assessment was ordered to determine if Matthew Raymond can be found criminally responsible for the crimes he has been accused of.

He is charged with four counts of first-degree murder in the deaths of Fredericton police constables Sara Burns and Robb Costello, and civilians Donnie Robichaud and Bobbie Lee Wright.

Raymond, who is in his late 40s, was previously found fit to stand trial after a shorter assessment, although details of the arguments seeking the assessments are under a publication ban.

He is alleged to have fired from his apartment window with a long gun, killing the two civilians as they loaded a car for a trip on Aug. 10, and the two police officers as they responded to the scene.

Raymond has previously told a judge there is evidence that would allow him to be "exonerated" immediately because of temporary insanity.

Following the last court appearance, defence lawyer Alison Menard said the longer assessment is to assess the mental state of an accused at the time of an alleged offence.

"Did they suffer from a mental disorder which would exempt them from responsibility?" she said outside court.

Nicole O'Byrne, a law professor at the University of New Brunswick, said in certain circumstances, people can be found not criminally responsible because they are lacking the intent element of the offence because of a mental disorder.

"A mental disorder as legally defined says that the person lacked the capacity to make a choice at the relevant time period to choose the bad act and to have planned it, such to incur criminal liability," she said in an interview.

O'Byrne said no matter what the outcome of the psychiatric assessment, it is still up to the judge to determine if there was no criminal responsibility due to a mental disability.

"You just don't send somebody off to the doctor and they say that person didn't have the capacity, because that's actually a legal determination whether somebody is criminally liable or not. That stage of where the doctors examine a person can be evidence of a person having a mental disorder defence, but it is not determinative of it," O'Byrne said.

Raymond has not entered a plea to the charges.

He has been very vocal in court, often complaining about the jail-issued orange jumpsuit he's been given to wear.

During his last appearance, Raymond told the judge that he was upset with case documents given to him by his lawyer, because he said only the court should have them.

The documents concerning the investigation are under a publication ban, but Raymond said guards where he's being held are able to see them.

He said a guard came into his cell in the middle of the night and was looking at the documents.