OTTAWA — Mental illness alone seldom explains why some people kill their spouses and children, according to Canadian experts in psychology and family homicide.

Sources told the Calgary Herald that Joshua Lall — who killed five people, including himself, inside an upscale Calgary home earlier this week — recently reported hearing voices and thought he was possessed by the devil.

Calgary police confirmed late Friday that Lall stabbed his family to death, along with a tenant in his home, on Wednesday morning.

But Martin Daly, a professor in neuroscience and behaviour at McMaster University in Hamilton, said mental illness is seldom enough to drive someone to kill his whole family.

“People with major psychiatric disorders are scarcely more violent than the rest of the population,” Mr. Daly said Friday. “They are commanded by the voices to do things like jump in front of a train [or] leap out of a window because they think they can fly – or go to the top of a mountain because they believe they will be taken away by a flying saucer.

“Guys who off their whole family are typically not mentally ill. They’ve decided to do this over some period of brooding and made a plan.”

Lall, 34, his 35-year-old wife Alison, and their two daughters, Kristen, 5 1/2, and Rochelle, 3 1/2, were found dead in their home on Dalhart Hill in northwest Calgary on Wednesday.

Their one-year-old daughter, Anna, was unharmed.

Journalist Amber Bowerman, 30, who was renting a basement suite in the house, was also killed.

Don Dutton, one of the country’s foremost experts in domestic homicides, said most men who kill their wives and children are severely depressed.

“They’re at the point where they can’t see any point of going on,” said Mr. Dutton, a psychology professor at the University of British Columbia. “Their depression is absolutely unmanageable, unescapable, and they feel they failed in some crucial way.”

He said depression can manifest in ways that cause the sufferer to blame the people closest to him — his wife, even his children.

Mr. Dutton has testified in high-profile cases, including the O.J. Simpson trial and a recent inquiry into why Peter Lee, a man from Victoria, B.C., killed his wife, his son, and himself last year.

A murderous rage can also be triggered by pathological jealousy, where the husband may believe his wife has been cheating on him or is leaving him, Mr. Dutton said.

He said the decision to kill one’s own children, usually seen in the public’s eyes as innocent victims, can also have religious or symbolic connotations for the killer.

“The murder of their children can happen for a couple of reasons. If they’re very religious, they want to see the child in heaven,” Mr. Dutton said. “If they’re not religious, they don’t want the child left on their own, because there would be no one to look after them, as bizarre as that sounds. They want to take everything with them.”

Most men who commit these grisly crimes are usually described by friends and family as loving, doting fathers and husbands.

“Usually in these cases, the men are completely normal people. It’s rarely the psychopath, someone with anti-social behaviour, a drug dealer,” Mr. Dutton said. “It’s someone trapped in the normalcy of things and having it collapsed in on them.”

Many domestic murder-suicide cases also follow patterns that are highly symbolic for the killer.

For instance, Mr. Dutton said, Lee may have killed his wife and children in different areas of their million-dollar home, but brought their bodies together before stabbing himself to death.

Mr. Dutton said this happens because the killer wants to join his family in death.

In this most recent case, he said, such symbolism doesn’t seem to have been a factor, since investigators found Lall, his wife, his children and the tenant in separate areas of the home.

Jordan Peterson, a clinical psychologist and professor at the University of Toronto, said whatever factors contributed to the killings — rage, jealously, depression, paranoia or something else entirely — substance abuse could make those black emotions far worse.

“Alcohol can take a bad situation and make it a really bad situation, really fast,” MR. Peterson said.

“The murders wouldn’t have been caused by a single incident, unless it was an extreme violation, such as infidelity. It would’ve been cumulative of a series of events.”

He also said Mr. Lall doesn’t fit the typical persona of a family-killer — someone who’s almost always a man aged 15 to 26, or in his 40s or 50s.

Peterson Lall’s decision to use knife in the killings may have been due merely to its availability.

“Usually, in domestic homicides, men use knives because they’re more common,” he said. “There’s one in every house. In the U.S., it is more likely to be guns.”

Mr. Peterson also offered a possible explanation for why little one-year-old Anna was spared.

“Babies are innocent. You have to be bloody out of your mind to kill them,” he said.

“That could’ve been his limit. He hit his limit and was so overwhelmed by the realization of what he had done that he had to stop.”

CALGARY — Alison Lall fought to protect her two young daughters as her husband, Joshua Lall, went on a murderous rampage armed with a knife, police revealed on Friday.

After killing his wife, two daughters and a female tenant, Mr. Lall then went into the nursery containing his one-year-old daughter Anna where he stabbed himself to death.

Anna was found the next day crying in her crib.

“Based on the evidence at hand, it is our belief that Joshua Lall is responsible for this incident,” said Calgary police Inspector Guy Slater at a press conference on Friday.

Insp. Slater said it was premature to say if a mental breakdown triggered the killings, although it has been reported that Mr. Lall was hearing voices in his head and believed he was possessed by the devil.

Police said it was believed the killings took place on Tuesday evening with Amber Bowerman, a basement apartment tenant, being attacked first.

“It appears the basement tenant, Amber, was the first to die, followed by Alison and the two girls. Every indication is that Alison fought to protect her children. Joshua later took his life,” said Insp. Slater.

Defensive wounds on Ms. Lall indicate she fought back. But as for the basement tenant, Insp. Slater said: “There is nothing to indicate that Amber could have done anything in her situation. It was a surprise attack.”

Ms. Lall, 35, along with her daughters Kristen, aged five, and Rochelle, aged three, were found in the Lalls’ master bedroom on the upper floor of their home.

Ms. Lall’s mother, Sheila Fraser, described her daughter as completely devoted to her three young daughters.

“It’s just a tremendous loss,” Ms. Fraser said. “She was an absolutely beautiful human being who did everything and did it very well.”

Mr. Lall, aged 34, was found dead on the floor — again a result of multiple stab wounds — in the room where the sole survivor of the attack was located the next day. She appeared to have been left untouched, Insp. Slater said.

While police do not have a perfect timeline, they have concluded that the murder-suicide took place Tuesday night. “For all intents and purposes, we believe the evening was like any other evening,” Insp. Slater said.

Mr. Lall, an intern architect at Calgary’s Cohos Evamy, called in sick Monday, and on Tuesday he asked for the rest of the week off. Ms. Lall was a stay-at-home-mom. Ms. Bowerman, a journalist, was at a conference in Lake Louise Tuesday, and returned that evening.

Police assume Ms. Lall and the children were home when Ms. Bowerman was killed. While Insp. Slater said there was nothing she could do to defend herself, she was awake when attacked. The police have found nothing to indicate there were previous conflicts in the house.

The news of the killings and Mr. Lall’s possible mental distress have startled friends and family members who knew him as a doting father and a high-achiever.

He was a high-school valedictorian, track star and volunteer fundraiser for his local community association.

A close friend detected some anxiety from Mr. Lall during a visit a few weeks ago, but said it did not appear to be more than what he and his wife could handle.

“He was a little stressed with work,” said Jennifer Klein, who lives in Edmonton. “We talked about it openly when they were here.”

Mr. Lall also called his parents earlier this week and told his father that he had a “mental breakdown or something,” according to one news report.

However, Insp. Slater said it was too early to say what sparked Mr. Lall’s killing spree.

“I can’t say whether or not Joshua had mental health problems,” he said. “That is up to the medical experts to conclude.”

Police are still awaiting toxicology results for Mr. Lall, although Insp. Slater said there was no hint that he was intoxicated at the time. Further, the police were not aware of any anecdotal evidence that would suggest Mr. Lall was taking any medication.

As for motive, the police are left without an answer.

“I can’t even speculate on that,” Insp. Slater said. “The only person who knows that is Joshua himself.”

National Post, with files from Canwest News Service