As Vancouver police probe the possible murder of a baby in the city, CTV News investigates the difference between homicide and infanticide.

Stories of infants allegedly killed on purpose are shocking, unsettling, and rare – but when they do emerge, they attract a lot of attention.

One case was tried in August 2008, when a Surrey, B.C., woman was accused of drowning her baby boy in a backyard pool.

She pleaded guilty after Crown Counsel downgraded the charge from second-degree murder to infanticide – a charge criminology professor Robert Gordon says many people don't understand, and is inapplicable to fathers.

The law was adopted in Canada in 1948 because juries were refusing to convict mothers of murdering their own children. Infanticide was introduced as an alternative charge with softer sentencing.

"The penalties usually aim towards supporting and assisting the mother as opposed to punishing her," Gordon said.

The maximum sentence for infanticide is five years, but no conviction in Canada has resulted in a jail term longer than one year. There is no minimum sentence.

But for infanticide to be charged over murder, the criminal code states certain criteria must be met: the child must have been less than 12 months old, and the mother must have been suffering from some form of psychosis brought on by childbirth -- or even the effect of lactation.

"It is an attempt to recognize the fact that in the post-partum period there's a great deal of disturbance in the chemistry of the mother that's given birth," he said.

"As a result of that, her mind may be disturbed."

But Kirsten Kramar, author of Unwilling Mothers, Unwanted Babies, says the law has unofficially adapted since the 1940s to include mothers who face heightened social or cultural pressures as well.

"The reasons they kill almost always has something to do with the society in which they live," she said.

Many women who commit infanticide come from deeply religious backgrounds, she said, and don't see birth control or abortion as options.

"Instead, they try to conceal the fact that they've been sexually active and deny their pregnancy and simply allow the baby to die at birth."

Kramar says punishments for mothers have been getting harsher in recent years, a strategy she says is ineffective as a means of preventing infanticide.

But there may be hope for decreasing cases in Canada by making social workers, counselors and other support systems more readily available to young women. Kramar says infanticide is far more common in provinces that lack those resources.

"It tends to be young women who commit infanticide, women who are marginalized by ethnicity and (are) religious, so the more social supports that are in place, the more chance we have."

"Infanticide can be prevented, absolutely, with more social support."