Fang Chi Xue, 38, was treated for self-inflicted stab wounds to the arms and abdomen at Boston Medical Center and is expected to be arraigned on two counts of murder, Norfolk District Attorney William Keating said. She was 7 1/2 months pregnant.
Police were called to the family home in Quincy, just south of Boston, at about 10:30 Thursday night by the children's father, who had been at work during the attack. Authorities initially said a 14-year-old daughter who survived made the 911 call, but later said the girl called her father, and the father then called police.
The 9-year-old girl suffered stab wounds to her wrists, but authorities are also investigating whether she was poisoned. An autopsy is scheduled.
The mother apparently had tried to strangle the teen, Keating said.
Keating said the incident was sparked by an argument, but would not offer more details.
Whether Xue is arraigned in her hospital bed depends on her medical condition, he said.
The family lived in a neighborhood of modest two-family homes in the city of about 92,000 residents, and was rarely seen outside, neighbors said.
Yan Mei Lin, who lives across the street, said she occasionally saw the woman outside holding the younger child's hand, and they would exchange brief greetings in Mandarin. Lin, 26, said she was shaken by the killing. "It's scary," she said.
Elizabeth Kennedy, 76, who raised six children in the neighborhood, said she walked her two dogs past the blue-shingled house with yellow trim every day, but never saw the family. "I wanted to cry," she said when she heard of the slayings. "I could cry right now. I feel for that woman. It must have been a lot of pressure on her to do that."
Alison Goodwin, a spokeswoman for the state Department of Children and Families, said the agency is investigating, but would not say whether the department had been involved with the family in the past.
There have been five domestic slayings in Norfolk County in the past month, a pattern Keating calls "unnerving."
In late March, Kerby Revelus stabbed his 17-year-old sister to death in the town of Milton, then decapitated his 5-year-old sister before turning on his 9-year-old sister, who called police. Responding officers broke down the home's door and shot the 23-year-old man dead.
Another man is facing charges for allegedly killing his blind aunt March 23 in the Plainville apartment they shared.
"In conversations with other district attorneys, domestic violence is a growing problem across the state," he said. "I know in Norfolk County we're deeply disturbed."
The roughly 400-square mile county stretches from the Rhode Island border to the edge of Boston, and is made up of many middle class and affluent communities. The population as of the 2000 census was about 650,000.
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