© Reuters/Evan SemonAn unidentified woman reacts outside a townhouse complex following an overnight hostage-taking incident in Aurora, Colorado January 5, 2013.
The gunman and his three victims, as well as a woman who fled safely from the home at the outset of the violence and alerted authorities, were all believed to be related to one another, police spokeswoman Cassidee Carlson said.
But the motive for the killings was not immediately understood.
"We're trying to find out what set this guy off," she told Reuters.
A hostage-negotiation team called to the scene had sought to talk the suspect into surrendering for about five hours before police moved to shoot tear gas into the home at about 8:00 a.m. (10:00 a.m. EST/1500 GMT), prompting the gunman to open fire on officers from inside, police said.
About an hour later, the gunman began firing at police again from a second-floor window, and police returned fire, killing the suspect, according to a police statement following the incident. No police were wounded.
Officers entering the townhouse found the bodies of the gunman and three other people - two men and a woman - who were presumed to have been shot hours earlier before police were called to the scene.
"None of the officers heard gunshots until they were directed at us at about 8 o'clock," Carlson said. The woman who escaped the home also told police the victims were shot before she fled.
The names of the gunman and his three victims were being withheld until the coroner could confirm their identities and notify next of kin, authorities said.
