EAST GREENBUSH, N.Y. – A mother despondent over her son’s suicide killed her two young daughters and herself early Tuesday using suffocating nitrogen gas at their home, about a week after a stay in a mental institution, authorities said.

East Greenbush Police Chief Christopher Lavin said a 911 call at about 1:45 a.m. sent police to the town house in the Albany suburb of East Greenbush, where they found the mom and girls, ages 6 and 9, unconscious from exposure to the odorless gas in a first-floor bedroom.

Rescuers had to break down the door to the locked room and tried CPR for a half hour before the three were taken to Albany Medical Center, where they died.

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

“I just think she couldn’t take it,” the woman’s brother, Bernard Pamberi, told reporters outside the home as he fought back tears.

Police said the father of the girls, Callidora and Eudora Thurston, has been notified.

Angela Mtambu was a traveling nurse who was working in Houston this spring when she decided to return to the home she has owned for 12 years. A Texas relative who was concerned that the distraught Mtambu might be planning to kill herself and her daughters notified authorities in East Greenbush, and an Amber Alert was issued June 1.

Mtambu was taken into protective custody in Harrisburg, Pennsylvania, and local social services took custody of the two girls, Lavin said.

Mtambu was kept nearly three weeks for psychiatric observation before being allowed to reunite with her daughters.