AURORA, Colo. -- A police chief says a Colorado shooting suspect's apartment is posing a "vexing problem" as officers face challenges in safely entering the residence where booby traps were set.
Colorado firefighters are monitoring the Aurora apartment building for gases in an effort to determine what chemicals they say 24-year-old James Holmes might have used to trap the place.
Holmes is the suspect in a mass shooting Friday at a midnight screening of "The Dark Knight Rises." Twelve people were killed in the attack and dozens were injured.
Aurora Police Chief Dan Oates said photos of Holmes' apartment appeared to show trip wires, jars full of ammunition and liquid and other items unlike anything the chief has ever seen.
The building and several around it have been evacuated.
Kaitlyn Fonzi, 20, a graduate student at University Hospital, said she lives in the apartment below that of the suspect.
About midnight, Fonzi said she heard techno-like, deep-based reverberating music coming from that unit apartment. She went upstairs to the suspect's place and put her hand on the door handle. She felt it was unlocked, but she didn't know if he was there and decided not to confront him.
"I yelled out and told him I was going to call the cops and went back to my apartment," she said.
Fonzi called police, who told her they were busy with a shooting and did not have time to respond to a noise disturbance. She said she was surprised to learn later that the apartment was booby trapped and was shaken by the news.
"I'm concerned if I had opened the door, I would have set it off," she said.
Fonzi said she had seen the man one or two times before but never talked with him.
She said she believes the music was on a timer because it started about the time of the shootings.
Police have searched apartments and broken out windows at the building, but Fonzi said she doesn't know the condition of her apartment or car.
When asked about plans to possibly try to detonate the device with a robot, she said, "It's not ideal situation, but if that has to be done to keep safe, then it has to be done."
University of Colorado pharmacy student Ben Lung, 27, who lives two floors down from the suspect, said he and other residents were evacuated around 2 a.m. by armed SWAT officers armed with rifles.
"I heard a loud crash. It sounded like an air conditioner falling to the ground. About 10 minutes later, I heard police knock on my door. Police were armed with assault rifles and they brought us outside the apartment building and started questioning us," Lung said.
Lung said a few residents upstairs had called police around midnight and complained about loud music coming from the suspect's apartment.
Michelle Thuis, 26, who lives in an apartment near the entrance to the building, said police woke her up when they stormed in around 2:30 a.m.
"I heard them breaking down the front door. I called the police on them, then I looked out and saw it was the police," she said.
Thuis described the building as quiet and populated largely by students and doctors affiliated with a nearby University of Colorado Denver medical campus.
The American Red Cross set up a shelter at Aurora Central High School for people evacuated from their residences because of the police search and monitoring.