A psychologist testified an Ottawa Mountie was suffering with PTSD to the point that he and his young son were "stuck in a masochistic relationship" when he shackled and burned the 11-year-old boy in the basement of the family home.

The disturbing evidence came at the trial of the 44-year-old Mountie and his wife, the boy's stepmother.

In February 2013 the couple pleaded not guilty to aggravated assault, failing to provide the necessaries of life and forcible confinement.

The father also faces charges of sexual assault causing bodily harm and assault with a weapon. His 37-year-old wife was charged with assault with a weapon.

There is a publication ban on naming those involved in the trial, including the psychologist, in order to protect the identity of the boy who is now 14 years old.

Psychologist says Mountie had PTSD

In court Wednesday, the Montreal-based psychologist said he started treating the accused a year after his arrest and estimated they have met more than 40 times for one hour sessions.

The psychologist testified, through a French interpreter, that he diagnosed the Mountie with PTSD, depression and Dissociative Identity Disorder.

He said this was due to the childhood trauma the man claims he endured from being sexually assaulted several times as a young boy growing up in war-torn Lebanon in the late 1970s.

The Mountie's lawyer, Robert Carew, asked the clinician if he thought the man was being sincere about what he says happened when he was eight years old.

'His flashbacks were his reality'

"It's likely to be true" he said.

The psychologist says the man's past trauma caused flashbacks to the sexual assaults and it caused him to frame all things around him through a violent and sexual lens. He added the man complained his son was continually defiant and displayed inappropriate sexual behavior.

"His flashbacks were his reality," he said. "He was living them as if they were true and not just things going through his mind."

The court heard the psychologist testify that when the man shackled and tortured the boy in the basement he viewed his son as a powerful enemy who had the ability to "sexually seduce his wife and brothers." The psychologist quickly added that he was not testifying that is what happened but rather to show the man's state of mind.

"As strange as it may appear, the son was so powerful to [the father] that he thought the boy was possessed by the devil," the psychologist said.

Father and son in masochistic relationship, psychologist says

Then the psychologist brought up masochism — deriving of pleasure from pain — saying that while it was difficult for the public to talk about, it was a "good time to address it."

He said the man and his son were "stuck in a kind of masochistic relationship" whereby the father repeated the violence and trauma he experienced on his son because he believed the boy was constantly seducing him, like his attackers.

The psychologist said with masochism the punishment must increase to achieve pleasure, so the man continued the hitting and burning hoping "the avoidance would be triggered."

The father told the psychologist his son wanted to perform sexual acts with his friends and that may have led to the Mountie burning his son's genital area.

Again the expert testified that he was not speaking to the truth of the child's statement — just the man's mental state at the time.

Father didn't think actions were wrong

Lawyer Robert Carew asked the psychologist when the son was being assaulted whether the Mountie knew what he was doing was wrong.

"As strange as it seems the man thought he was protecting his family from the boy and he couldn't see the problematic nature of what he was doing," said the psychologist.

Throughout most of the testimony the accused sat in the front row of the courtroom with his head down.

Earlier in the day Superior Court Justice Robert Maranger ruled the psychologist's expert evidence was admissible.

Psychologist evidence ruled admissible

Crown prosecutors fought to have the evidence declared inadmissible saying the psychologist lacked the credentials to diagnose PTSD because he refused to use scientifically recognized criteria for such a diagnosis.

They added the clinician could not provide independent, objective evidence because he was still treating the Mountie and he would feel a stronger loyalty to protect his patient.

Defence lawyers argued the psychologist had more than 40 years clinical experience and he currently was treating 100 patients with PTSD.

Justice Maranger told the court he had reservations — acknowledging the expert did not have any forensic experience nor had he ever provided opinion on a case involving whether an accused was not criminally responsible.

In ruling the evidence was admissible, the judge concluded by saying it would be on "the lowest spectrum" of expert evidence.

The psychologist continues testifying on Thursday.