Leshanda Armstrong, the 25-year-old who drove her van into the Hudson River Tuesday, drowning herself and three of her four children, is an enigma to psychiatrists who have little idea how mothers become murderers.
New York police have ruled it a murder-suicide. Only her 10-year-old son Leshawn escaped from a window in the sinking vehicle and swam 25 yards in cold waters to the shore.
More than 200 mothers a year kill their children, according to the American Anthropological Association, and little is known about maternal filicide.
In the last quarter of the 20th century among children under age 5 killed in the United States, about 61 percent died at the hands of parents; about evenly split between mothers and fathers, according to research by Susan Friedman, a psychiatrist University Hospitals of Cleveland/Case Western.
The U.S. has one of the highest rates of child homicide compared with other nations -- an estimated 8 per 100,000 infants. Canada, for example, has 2.9 per 100,000.
"Although women who kill their children are often labeled as 'mad' or 'bad,' no consistent approach exists for defining the population of offenders," said Friedman. "Factors associated with maternal filicide appear to be nonspecific but seem likely to include past use of psychiatric services and a history of suicidality and depression or psychosis."
Murderous mommies do make shocking headlines. In 1994, in a similar case, Susan Smith strapped in her two young sons and drove a car into a South Carolina pond. The car sank as the children slept. She is currently serving a life sentence for the two murders.
In 1983, Diane Downs shot three of her children, killing one. A 27-year-old divorced postal service worker from Oregon, she claimed a stranger had shot her children. Downs' story about the stranger did not add up. Reading through her secret diaries, police found a motive: an obsession with a married man who didn't want her children.
In February 1984, she was arrested and charged with one count of murder and two counts of attempted murder. She was later sentenced to life plus 50 years.
In 2001, Andrea Yates killed her five young children in the bathtub in her Texas house. Then 36, she had suffered for years from post-partum depression and psychosis. Yates was convicted of capital murder and sentenced to life in prison, but in 2006, a jury found her not guilty by reason of insanity. Today, she is committed to a high-security mental health facility.
According to Friedman, there are typically five motives which might drive a parent to kill their child. The most common is a result of maltreatment or chronic abuse.
Others include altruistic killing, when the parent is mentally ill or believes the child may be suffering. Another motive is seen in murders just after the birth of an unwanted child. Psychosis is another motivator.
Rarely, a parent seeks revenge against a partner by killing their child in what is called "Medea syndrome."
Suicide murders are more often seen among fathers than mothers, but about 20 to 25 percent of women commit suicide within 24 hours of killing their children.
Methods used by women are also "gentler," according to Friedman. "You are more likely to see strangling or many fatal blows among fathers."