Sheriff's officials said Thursday that Michael Sheer killed his father, 55-year-old Mark Harrison Sheer; his mother, 54-year-old Lydia Ann Sheer; and his 15-year-old sister Amy at the family's home in Mission Viejo.
Deputies responded to reports of gunfire and a man yelling on Monday, according to the station. Lt. Jeff Hallock said, "Deputies patrolled the area for several minutes, but were unable to locate anything to substantiate the report."
On Tuesday, CBS Los Angeles reports the officers discovered the bodies of the victims after receiving a call for a welfare check at the Sheer residence.
"Based on the preliminary investigation and evidence located inside the residence, Michael Sheer, 21, is suspected of shooting his father, mother and sister with a shotgun before turning the gun on himself," said Hallock.
Police did not discuss a motive for the crime.
Those with additional information are asked to call the Orange County Sheriff's Department Homicide Unit at (714) 647-7055.