Authorities say a mother despondent over her son's suicide has killed her two young daughters and herself using suffocating nitrogen gas in an upstate New York home.

Police got a 911 call to the house in an Albany suburb around 1:45 a.m. Tuesday. Police Chief Christopher Lavin says the mom and her daughters, ages 6 and 9, were found in a first-floor bedroom in grave danger after being overcome by the gas.

Lavin says rescuers tried CPR for a half hour before the three were taken to Albany Medical Center, where they died.

He says the mother, 47-year-old Angela Mtambu, was recently released from a mental institution after being overcome with grief when her 23-year-old son asphyxiated himself in the home in April.