Women are stereotypically nurturing and less threatening, and therefore images of women who are accused of molestation, such as the defendant in the Sandra Cantu case, jar our sensibilities, said crime experts.
When women are the perpetrators, they are often psychotic, according to Judie Alpert, a professor of applied psychology at New York University, who works with adults who were abused as children.
Often unreported, cases of female abusers show they are often victims of sexual molestation or emotional abuse themselves.
"Males are motivated by a lot of things, but they are usually not as unstable," she told ABCNews.com. "Men are more likely to abuse alone."
"Sometimes women participate with their husbands and abuse when the partner abuses," Alpert said. "Sometimes a married couple does it as part of ritual abuse."
"They are either repeating something that was done to them, or trying to understand it, or they are completely out of touch with reality," she said.
What makes the Sandra Cantu case more confounding to criminologists is the dual molestation and murder charges, according to Kenneth V. Lanning, a retired 30-year veteran of the FBI and police consultant on crimes against children.
Sexual molestation and murder rarely go hand-in-hand, he told ABCNews.com.
"The vast majority of child molesters do not abduct and kill their victims," said Lanning, who has no involvement in the case.
Strangers typically trick a child into sexual molestation -- by asking for help in finding a dog, "but they don't typically force or injure and kill the child," Lanning said.
"When it's an acquaintance, like a neighbor or baby sitter, the kid is groomed, seduced and manipulated," he said. "For a 6-year-old it might be a game, fooling around playing doctor. As a result, it decreases the likelihood that the child will tell anyone about it."
Lanning said police do best when they see molestation and murder as separate crimes, but sometimes the two overlap.
"What happens in some cases and what causes violence against the child is when the [predator] is grooming or seducing or manipulating and it didn't work out right," he told ABCNews.com. "They play games and the child goes along, then it gets carried away and they do something, and the child says, 'It hurts, I don't like it tell, I'll tell mommy.' That may cause the killing of the child."
Females can often disguise their sexual crimes because of the trust that is placed in them as caregivers, he said.
"Women are viewed as a lot less threatening, and they can get away with what men can never get away with," Lanning said.
Still, he said with the overwhelming evidence about the relative scarcity of female molesters, he often gives controversial advice.
"When women come up to me and ask what is the one thing I can do to protect my child from a baby sitter -- and this is a terrible thing to say and people are offended -- I say the simplest thing an average person can do is never hire a male to watch your children," he said.