No one wants to believe a mother is capable of murdering her children.
"It's extremely rare," said best-selling author Ann Rule.
When the Seattle crime writer heard about Susan Smith's claim that a stranger had stolen her car and abducted her two young boys, another case came to Ms. Rule's mind.
"The minute I heard about it, I had my own feelings of deja vu," said Ms. Rule during a telephone interview yesterday.
She remembered Diane Downs, the mother from Eugene, Ore., who claimed one night in May 1983 that a stranger had flagged down her car on an isolated rural road and shot her three children. One child died; the other two were severely wounded. Downs was later convicted of shooting her children.
Ms. Rule spent three years writing "Small Sacrifices," a best-selling book on the case that was turned into a TV movie starring Farrah Fawcett. Her work on the book made her more attentive to child-abduction cases.
Ten days ago, Ms. Rule heard news reports about Ms. Smith, a Union County, S.C., mother who claimed a black man with a gun stole her car and drove off with her two sons, 3-year-old Michael and 14-month old Alex.
"My first reaction was 'Oh, that poor mother,'" said Ms. Rule. But, as a former police officer, Ms. Rule grew skeptical of Ms. Smith's story.
For one thing, she said, most car jackers only want cars. If they discover kids after they've taken the car, they usually leave the kids.
Ms. Smith told investigators the gunman would not allow her to take her children, saying he didn't have time.
"Most mothers would die protecting our babies," said Ms. Rule, mother of four children and a foster son.
The entire nation, it seemed, kept a 10-day vigil hoping to hear of the safe return of the Smith children. Police yesterday found Ms. Smith's car in a South Carolina lake with two bodies inside. She was charged with two counts of murder in the deaths of her sons.
Dr. Herbert Modlin, a Topeka, Kan., forensic psychologist, has testified about the mental conditions of women accused of killing their kids.
"The roots of it are kind of irrational usually," said Dr. Modlin.
Experts say some of the mothers are poor, young, uneducated women who can't handle the responsibilities of motherhood. Others have psychiatric disorders. Still others are impaired by drug or alcohol abuse.
Still other child-killers are driven by guilt. "The children are often seen as products of sin -- sex is sin, in other words," Dr. Modlin said.
Some mothers kill their children while in the throes of postpartum depression. But mothers who kill toddlers are even more rare, Dr. Modlin said.
Statistics don't show how often mothers kill their children. But child murders, in general, are rare. In 1992, five North Carolina children under the age of 1 were murdered, according to the State Bureau of Investigation. Ten more between the ages of 1 and 5 were killed.
Ms. Rule said women kill for different reasons than men. Those reasons usually involve love -- including revenge or jealousy -- or money.
"They plan their murder much more carefully than men do," said Rule. "They tend to kill someone they know, someone who is related, someone who trusts them, someone you would expect them to protect."