A 16-year-old boy called police Monday night to say his family members were injured or killed in the house, Fontana police Sgt. Doug Imhof said.
Police arrived to find a bloody scene with the bodies of a boy about 10 years old, a girl about 12 years old and a man and woman each about 35 or 40 years old, Imhof told KNBC-TV and KABC-TV.
Fontana police Chief Rodney Jones told KNBC that the deaths were homicides.
It appeared all four lived in the home, Imhof said, but police did not immediately say what their relationships were.
Detectives found the bodies and blood spread throughout the house, but had stopped the investigation while they sought a search warrant, police Imhof said.
“There is some amounts of blood in different areas of the house,” Imhof told KABC. “There’s a couple of weapons that have been seen by our detectives just looking, but they haven’t been able to search the house because they can’t until they obtain a search warrant.”
Beyond his mention of the weapons, Imhof gave no indication of how the people may have been killed or who the killer may have been, and it was not clear why a warrant was needed.
Neighbor Jessica Arauz told KABC there was arguing coming from the house earlier in the evening.
Phone messages left with police by The Associated Press were not immediately returned.
The home is in Fontana, a city of about 200,000 people in San Bernardino County about 50 miles east of downtown Los Angeles.