A man shot and killed his three daughters and their chaperone before turning the gun on himself at a church in California on Monday.
The girls aged nine, 10 and 13 were attending a supervised visit with their father when the incident occurred.
The name of the estranged father (39) has not yet been released.
The shooting took place at 5pm in Sacramento's Arden-Arcade neighbourhood, according to Sergeant Rod Grassman from the local sheriff's office.
Mr Grassman told reporters investigators were looking for clues for a motive but believed the shooting stemmed from a domestic dispute.
He said: "This was not a random shooting."
He added that the gunman and his victims "knew each other."
An employee at the Church in Sacramento who was on the upper floor of the building at the time of the shooting told authorities he heard the shots and ran out of the building to call the police, Sergeant Grassman said.
He added that sheriff's deputies who attended the scene found five people shot to death.
Investigators cordoned off the scene and remained there overnight.
California Governor Gavin Newsom said his office was working with local officials.
"Another senseless act of gun violence in America - this time in our backyard. In a church with kids inside. Absolutely devastating," Mr Newsom tweeted.
