AURORA, Colo.—Four people, including an armed suspect, died after an hours-long police standoff Saturday at a Colorado townhome, authorities said.

Police Sgt. Cassidee Carlson said a SWAT team was called after gunshots were heard at the Aurora, Colo., home at about 3 a.m. Investigators said three victims, all of them adults, appeared to have been killed before officers arrived.

Carlson said the suspect shot at officers at about 8:15 a.m. and was killed during a gunfight about 45 minutes later when police entered the home. It remained unclear if officers shot the suspect or if he shot himself.

A motive for the killings also was unknown.

"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. "This is a big investigation, and a lot is entailed."

A fifth person escaped uninjured before officers arrived and reported that she saw three people inside the home who "appeared lifeless," Carlson said. The sergeant declined to elaborate about the woman's escape.

Police declined to release the name of the suspect or the victims.

Violence marred Aurora and put the Denver suburb in the national spotlight nearly six months ago when a gunman's bloody rampage inside a movie theater left 12 people dead. Prosecutors will go to court Monday to outline their case against the suspect, James Holmes.