It's a crime older than the Bible, cuts across all cultures and is more common than one might think. But the murder of children by their parents - filicide - still remains one of the most shocking acts of domestic violence, and one of the most studied.
In journals on law, psychology, criminology and ethics there have been upward of 100 studies since the 1950s that have tried to understand the minds of mothers and fathers who kill their sons and daughters.
Researchers have found acute psychosis, spousal revenge and accidental maltreatment to be among the causes. But by far, they find the leading motive to be "altruism" - the warped belief that parents are acting in the best interests of a child who will be better off dead than left to live in a cruel world under dire circumstances.
It is this tragic thinking, police suspect, that led a Quebec couple to kill their three children, Joëlle, 12, Marc-Ange, 7, and Louis-Philippe, 4, on New Year's Day and then attempt to kill themselves. The father, Marc Laliberté, died of his wounds. But the mother, Cathy Gauthier-Lachance, survived.
Jobless, bankrupt and depressed, the couple apparently forged the murder-suicide pact as a New Year's resolution, police say.
It was in 1969 that Cleveland psychiatrist P. J. Resnick completed a landmark study on filicide, reviewing cases between 1751 and 1967, and found "altruism" to be a major, unique cause in child homicide cases.
More recently, University of Alberta psychologist Dick Sobsey wrote in a 2001 article that 80 per cent of the children murdered in Canada are killed by their own parents - and that roughly half of these parents say they acted "altruistically."
Dr. Sobsey's paper, which appeared in Health Ethics Today, cited a report from the RCMP suggesting the number of parents killing their children in Canada had climbed -from an average of 32 children between 1990 to 1993 to 49 between 1994 and 1998.
Some research suggests it is more rare for parents to commit suicide after killing a child, but more likely to occur if the parent has killed more than one child and has killed older children.
Recent research shows that both fathers and mothers commit the crime. However, few papers note cases in which mothers instigate the killing of multiple family members as well as their husbands. But several reports note that parents are likely to be suffering from mental illness at the time of the murders.
Some acquaintances and former colleagues who knew the couple in Chicoutimi have said they believed both were suffering from depression and burnout.
Financial distress, or the fear of it, has also been pegged as a trigger in other cases. Most recently this has been seen in Asia, where the number of parents killing their children and themselves has spiked. In Hong Kong, for example, experts say there have been as many murder-suicides in the past five years as there were in the previous 15.
In October of 2007, a 36-year-old wife of a cancer patient fearful for the future of her children bound the hands and feet of her son, aged 9, and daughter, 12, and pushed them from the 24th floor of their apartment. She then leapt out after them, according to a report in the South China Morning Post.
The paper also reported that last August, a 33-year-old father in financial ruin gassed himself and his three-year-old daughter to death in the bedroom of their home.
Experts at the University of Hong Kong conclude "the killers' thinking is distorted to the extent that they convince themselves that they are acting out of love and in their children's best interests."