OTTAWA -- A former Mountie who restrained, tortured and sexually abused his son in the basement of their family home was suffering from post-traumatic stress disorder, a forensic psychiatrist told an Ottawa court Wednesday.

Dr. Helen Ward also told a sentencing hearing the former officer should have known enough to seek treatment for both his PTSD and depression, but didn't because he believed everyone else was wrong except him.

The man, who cannot be identified under a court order aimed at protecting the identity of his son, sat silently in the courtroom as the first full day of testimony in his sentencing hearing got underway.

In November, he was found guilty of aggravated assault, sexual assault causing bodily harm, forcible confinement and failing to provide the necessaries of life.

He was initially arrested in 2013 after the boy was found wandering in a neighbour's back yard in search of water.

Court heard the boy nearly starved to death during his captivity, which left him chained and shackled, often naked, in an unfinished basement.

Ward, who was testifying as a defence witness, said the former officer exhibited "chronic and severe PTSD" while he was undergoing a court-ordered psychiatric evaluation, although she said the symptoms "fluctuated over time."

He was "re-experiencing" behaviours he was subjected to as a child, including flashbacks, expressed hopelessness and at times denied his own actions, Ward testified.

The former officer, who was fired from his job in December after initially being suspended, testified during his trial how he was abused as a young boy, and how he experienced armed conflict while growing up in Lebanon.

Court also heard the man refer to his son as "the devil" as he described how he was concerned he'd grow up to be a sexual predator.

"I think there's a link between what (the officer) experienced (as a young boy) and how he perceived his son," Ward said of the officer Wednesday.

"(He) clearly had a distorted view of his son."

But the former counter-terrorism officer also could have sought treatment for his own psychological issues but didn't, she added, linking his behaviour to narcissism.

"I think he believed that he was right" despite what others were telling him, Ward told the court.

Court also heard Wednesday from the boy's maternal aunt, who criticized the justice system and medical professionals for their roles in allowing the abuse to continue.

"The internal invisible damage will be with him forever," the woman said of her nephew as she read from a victim impact statement.

"Individuals and institutions put in place to help him failed."

The former officer's wife, the boy's adoptive mother, was also found guilty of assault with a weapon and failing to provide the necessaries of life in November and was later handed a three-year sentence.

The boy was 11 when his parents were arrested in February 2013.

His aunt recalled the night when news reports first alerted the family to the boy's escape from the family home in suburban west Ottawa.

"I remember feeling the dread," she said as she described how the former officer had for years denied the boy access to his biological maternal family.

The man sought and was granted full custody of the child when the boy's mother died in 2009, subsequently isolating him from his late wife's family.

"He can never get back the years that he lost," the aunt said, her voice shaking. "He was so tiny and vulnerable."

The sentencing hearing is expected to last three days.