Two mothers, acting independently and living on opposite sides of the country from each other, are believed to have killed their children and themselves in recent days.
The alleged killings come on the heels of a disturbing, recent string of family murder-suicides, which criminologists and forensic psychiatrists call familicides.
Though rare, experts say familicides tend to occur in clusters.
Police believe Andrea Roberts, 41, a stay-at-home mother, killed her two children, ages 11 and 7, and her husband, Michael, before turning the gun she used to kill them on herself. Neighbors found the bodies in their home in an upscale Dallas suburb.
Tuesday the bodies of a 44-year-old woman, her 10-year-old son and 7-year-old daughter were found inside a Delhi Township, Ohio, house. The deaths are being investigated as homicides, although murder-suicide was "certainly a possibility," Hamilton County Coroner O'dell Owens told The Associated Press.
Women are more likely to kill their children than men are, but men are more likely to kill both their children and their spouse, said Dr. John Bradford, head of the forensic psychiatry department at the University of Ottawa.
Experts said that men and women are often motivated to kill their children for different reasons.
Unlike men, who often are driven to familicide by feelings that they have failed to adequately provide for their kids, women often kill their children out of a delusional sense of altruism.
Women's attempts at suicide often fail, said Dr. Phillip Resnick, a psychiatry professor at Case Western Reserve University, and their crimes are therefore less likely to be classified as familicide.
Sametta Heyward, 27, was accused Tuesday of leaving her two young children in a hot car in Hanahan, S.C., while she was at work. She was charged with homicide by child abuse after their bodies were found wrapped in trash bags under an apartment sink, the AP reported.
Though it seems likely that Hayward's children were killed as a result of neglect, women are often driven to kill their children by a psychotic impulse to help them.
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, according to Bradford.
"When you're psychotically depressed the whole world appears as if you're looking through dull gray glass," Bradford said. "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."
Severely psychotic women, Bradford 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."
Men and women who kill their children, forensic psychologists and criminologists told ABC News, tend to be severally depressed or psychotic and do not simply "snap" but usually have long histories of mental illness.
In June, wrestler Chris Benoit made headlines when he was found to have killed his wife, his 7-year-old son and himself in the family's Fayetteville, Ga., home.
Benoit's wife, Nancy, 43, and son, Daniel, were each found in different rooms and were believed to have been killed days before the wrestler took his own life.
Less than a week before the Benoit killings, New Jersey engineer Thomas Reilly and California businessman Kevin Morrissey each decided to kill their children and then themselves.
Reilly, 46, drowned his two young daughters, ages 5 and 6, in the bathtub of their Montclair, N.J., home before hanging himself from the attic rafters.
Morrissey, 51, shot his wife and two daughters in a parked car at a popular park near Berkeley, Calif., before turning his .357 handgun on himself.
Police investigating the deaths of Morrissey and his family said they found a note in which the 51-year-old father of two said he was distressed over the family's financial situation.
Morissey ran a skin care clinic with his wife, Dr. Mamiko Kawai, 40. The couple's two daughters were Nikki Morrissey, 8, and Kim Morrissey, 6.
Resnick, a psychiatry professor at Case Western Reserve University, said Morrissey may have been "severely depressed and believed his family was similarly miserable. He was ending the entire family's pain."
"Money is often an issue. The man sees himself as a breadwinner and may feel like he has to take the whole family out with him," Resnick said.
Police investigating the deaths of Reilly and his children, Megan, 5, and Kelly, 6, said they didn't yet know what motivated him to drown his daughters, but that he'd recently been separated from his wife.
"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.