"There are still many unanswered questions. The couple was separated, and he had visitation rights. The wife contacted police when she couldn't reach Reilly. There was no note, and the case is still under investigation," said Roger Terry, deputy chief of the Montclair Police Department.
Local, state and federal agencies do not specifically track familicides, and discrepancies in the way the crimes are classified make getting an accurate count difficult.
Hay Carter, a professor of criminology at Florida State University, however, said these crimes -- like all mass murders -- are rare.
Carter estimated that of the approximately 16,000 murders committed annually, less than 2,000 involved family members, including parents who kill their children.
Experts said there is a greater chance that a stepparent will murder a stepchild than a biological parent will kill his own child. They also said, despite the rarity, parents are more likely to kill their children than strangers are to abduct and kill them.
Experts said that women are often motivated to kill their children for different reasons than men are.
Rather than feeling they have failed to adequately provide for their kids, women often kill their children out of a delusional sense of altruism.
Women often fail at committing suicide, said Resnick, and their crimes are therefore less likely to be classified as familicide.
"Women try three times as often to commit suicide, but men are three times more successful," he said.
Psychosis and severe depression can lead women to believe they are killing their children to end their suffering or because they believe they are demonically possessed.
"When you're psychotically depressed the whole world appears as if you're looking through dull gray glass. When you look at your children, you see them through your own suffering and emotional pain and believe they, too, are suffering. You begin to think they and you would be better off in heaven. This is an altruistic delusion. The results are horrific, but it's done in the hopes of stopping suffering," said Bradford at the University of Ottawa.
Severely psychotic women, he said, "might not see their children as suffering but see them instead as evil. They believe their child is a devil and to protect mankind they must be killed."