A gunman has fatally shot three people inside a house in the United States, before killing himself, police say.

The gunman who is identified as Herman Derico, 42, killed two women and a man in a home in Oakland, California, late Wednesday night, Maine State Police said in a press conference early Thursday morning.

Two of the victims were the parents of a four-year-old girl who was found unharmed in the house.

Police found the bodies of Amanda Bragg, 30, and Michael Muzerolle, 29, the parents of the girl, and Amy Derosby, inside the house.

“We don’t have a clear understanding of why this happened,” Troy Gardner of the Maine State Police said.

He said an investigation is in underway into the deadly incident.

In another violent incident in California, police shot and killed a male student at the University of California, Merced, after he stabbed and injured four people as classes began on Wednesday morning.

Two of the wounded were transported to a hospital by helicopter and others were treated on campus.

Police said that two of those stabbed are students at the school and the two other victims are a staff member and a contract employee.

Every year, more than 30,000 people are shot and killed in the United States.

The US averages 87 gun deaths each day as a function of gun violence, with an average of 183 injured, according to the University of Chicago Crime Lab and the Centers for Disease Control and Prevention.