According to authorities, the couple had dated and broke up a few months ago, but they still kept the lines of communication open. The young woman went to the home on Tuesday to pick up the man to go out for the day, and when they returned, things seemed fine.
"They went out, went skiing or something, came back, were socializing at the house, the other family members in the house went to bed, and they awoke to the gunshots," said L.A. County Sheriff's Lt. Liam Gallagher.
There were six people inside the home at the time of the shooting, but nobody else was hurt.
Police were unsure who shot whom. The gun believed to have been used in the shooting was recovered inside the home.
The names of the victims have not yet been released.