KABC-TV said the father Ervin Lupoe was found dead with his wife Ana, their 8-year-old daughter and two sets of twins - 5-year-old girls and 2-year-old boys- on Tuesday. Police arrived minutes after the killings and said the smell of gunshot was still in the air.
Officers said they went to the house after the TV channel informed them that it had received Lupoe's telephone call and a fax saying that "he was despondent over a job situation and he saw no reasonable way out."
"Why leave our children in someone else's hands," Lupoe said in his letter that KABC-TV posted on its website.
In the letter, Lupoe said both he and his wife had been fired from the Kaiser Permanente West Los Angeles Medical Clinic, where they worked as technicians, and stressed that Ana had been involved in the planned killings, which was a way out of the family's financial problems.
However, police said Ervin was the main suspect as the gun was found next to his body.
The hospital said in a statement it was "deeply saddened to hear of the tragic deaths."