Police responding to reports of screaming and gunfire at a south Los Angeles home found four dead family members inside, officials said Thursday.

The victims of the apparent murder-suicide were a mother and father, both in their 20s, and their two daughters, ages 1 and 3, police Sgt. Michael Flanagan said.

Officers arrived at the scene Wednesday around 9 p.m., when another family member who had come to visit the home heard a commotion coming from inside, police said.

When police entered the house about two hours later after setting up a containment line, they found the four victims, all dead by gunshot wounds, Flanagan said.

Authorities said the victims were all believed to have died before police arrived.

The incident was under investigation.