LONGMONT, Colo. — Emergency phone line operators heard the sound of gunfire early Tuesday as a Colorado woman called 911 and was apparently killed by a man who then picked up the phone and told dispatchers he was going to kill himself before they heard the sound of another shot, authorities said.

Investigators think the unidentified woman and man were among four people found dead at a home near Longmont, about 35 miles north of Denver, in what police are characterizing as a murder-suicide.