Experts Seek Reasons Behind Irrational Crime : Theories: Psychiatrists say mothers who kill tend to be unwed and murder their newborns or are psychotic and kill their older children.

Among the sad, horrific cases of child killing, some of the most irrational involve mothers and their children, say forensic psychiatrists.

Except in the instance of women who kill their newborn infants, no amount or type of stress alone can account for women killing their children, said Newport Beach psychiatrist Park Elliot Dietz. “It doesn’t come from who you hang out with, what your opportunities in life are, or how much money you have. It comes from something being wrong with the person,” including mental illnesses such as schizophrenia or psychotic depression.

Among the 342 deaths of children under 12 in Orange County in 1990, a dozen were homicides--up from one in 1986, according to the Orange County Sheriff-Coroner’s Department.

This summer, a Santa Ana woman was charged with the death of her 3-month old daughter, whom she originally had reported kidnapped. Last year, a Cypress woman was accused of killing her newborn after the dead child was found in a bag in her home. An Anaheim woman was convicted in 1990 of killing her 6-week-old infant by running over the child with a car, but a judge overturned the verdict on grounds she was mentally ill at the time. And in one incident outside of the county, a Monterey Park woman was arrested last month on suspicion of stabbing to death her sons, ages 2 and 6.

Most commonly, child killing in the United States results from prolonged abuse, said Dietz, who evaluates cases nationwide. “These parents are no different from any other child-abusing parents,” he said. While they may suffer a personality disorder and abuse substances, they are not necessarily mentally ill.

Another form of perpetrator is the “family annihilator”--usually a father who kills his entire family including his wife, children, pets, and often himself.

They are often paranoid, depressed, middle-aged men who may be substance abusers also. While women may also be family annihilators, Dietz said he has not encountered one.

In general, he said, mothers who kill their children fall into two types: unwed mothers who have denied their pregnancies and kill their newborn in a crude manner, or those with a psychotic illness who kill their older children.

“One study that compared neonaticide with the older infanticides found that those killing newborn infants were usually responsible for their behavior and not mentally ill. Most of the mothers who killed their older children were regarded as seriously mentally ill and were found legally insane,” Dietz said.

Mark J. Mills, a forensic psychiatrist from Rancho Santa Fe, said that in general, mothers do not “snap” but rather deteriorate gradually over weeks, months or years. “Presumably her husband would have known she was ill and would have inquired whether the children were incorporated into her illness.”

“These days,” he added, “one has to ask about substance abuse. Particularly cocaine, or amphetamines. Those drugs can make people very crazy.”