The suspect shot at police who approached the front of the home with an armored vehicle and tear gas at about 8:15 a.m., and he was killed when he fired at officers from a second-story window about 45 minutes later, Carlson said. It wasn't known if officers shot the suspect or if he shot himself.
A fifth person escaped unharmed and called police to report that she saw three people inside the home who "appeared lifeless," said Carlson, who declined to elaborate about the woman's escape.
A motive for the killings was unknown. Police wearing gloves and carrying evidence bags were going over the crime scene.
"We're just getting in there with our crime scene detectives, so obviously we'll have to determine if it was our rounds or his rounds," Carlson said.
Police declined to release the name of the suspect or victims.
"We have an idea of who they are, but we obviously want to confirm their identities with the coroner," said Carlson, who declined to release the relationship between the victims and the shooter.
Officers evacuated neighbors' homes during the standoff and used a bullhorn to communicate with the gunman, urging him to surrender.
"After we arrived on scene, there were no more shots fired up until he fired at us," Carlson said. "During this time he was all over the house. He moved furniture. He was throwing things. He was agitated. He was irrational."
A large front window was missing in the modest two-story townhome, the window's mini-blinds in disarray. Bullet holes marked two upstairs windows, and neighbors milled about outside.
The shootings occurred about four miles southeast of the Aurora Mall, where 12 people were killed and dozens were wounded by a gunman at a midnight showing of "The Dark Knight Rises" on July 20. The man charged in that shooting, James Holmes, goes to court Monday for a preliminary hearing in which prosecutors will lay out their case against him.
Aurora, just east of Denver, is one of Colorado's largest and most diverse cities with more than 335,000 residents. It is home to Buckley Air Force Base as well as the sprawling University of Colorado Health Sciences Center campus.