It’s a crime so monstrous as to surpass comprehension. Yet its passion takes root in some of the most tender ground of human experience: pregnancy and motherhood.

What drives a handful of women to slice open the bellies of others to steal their newborns?

Researchers have uncovered hints. “You can describe it as sort of the maternal instinct run amok,” says psychiatrist Dr. Phillip Resnick, who has written about this kind of crime.

In East St. Louis, Ill., an innocent plea was entered Monday for Tiffany Hall, a 24-year-old woman charged with killing a woman and her fetus; investigators believe she cut the mother open with a pair of scissors. Authorities say Hall also told police she drowned the woman’s three other children. A judge ordered a psychological examination for Hall.

Such crimes are exceedingly rare in a country with more than 4 million births a year. Previously, only eight similar cases have been documented since 1987 by the National Center for Missing and Exploited Children. Yet they are frequent enough to have acquired a clinical-sounding name: newborn kidnapping by Caesarean section.

It is a variety of the more common crime of simply snatching an infant, experts say. Attackers are women of childbearing age who typically have lost a baby or can’t have one, mental health professionals say. They feel empty and fiercely long for a child to cement a shaky love relationship.

“They look at these pregnant woman and say, ‘Look at all the attention they’re getting. They’re complete,”‘ says N.G. Berrill, a New York-based legal psychologist. The attackers often fake their own pregnancy, take part in baby showers and prepare nurseries at home.

However, at some moment they cross a boundary and descend almost to Shakespearean depths of tragedy. “The meaning of being barren for some women is just extraordinary,” Resnick said.

Fashioning elaborate cons, they may trick a stranger into letting down her guard, or they may set upon a close friend without warning. The raw violence may vent a gusher of rage or jealousy directed at the pregnant victim.

The assaulted women nearly always die, sometimes bleeding to death. The attackers then claim the newborns as their own, even if only as stillborns to be buried. However, the newborns often live and eventually return to surviving family when the crime is solved.

Experts believe that the macabre surgery is strangely meant to fulfill a fantasy of really giving birth to the child.

More often the crime grows out of a personality disorder, experts say. While still in the realm of mental illness, such impulses may fail to meet the legal standard of insanity – a failure to grasp right and wrong. The attackers often hide the mother’s body afterward, seemingly aware they have done wrong.