The one-bedroom apartment rented by the suspect in Friday's shooting rampage inside a suburban Denver movie theater appears to have been rigged with an array of sophisticated booby traps that one official described as "unique."

The law enforcement official said that video shot by robots shows at least a dozen "victim-initiated devices" -- none of which appear to have been equipped with timers -- inside the apartment. "You normally don't see this situation," the official said.

Authorities hope to enter Saturday the third-floor apartment of James E. Holmes, who is accused of killing 12 people early Friday and wounding scores more in Aurora, Colorado, Police Chief Daniel Oates said.

Robots may return Saturday to shoot more video and/or to retrieve samples from inside the 850-square foot apartment, the first law enforcement official said.

It was not clear whether authorities were planning to detonate any of the devices.

"Jars of black powder" and what appear to be "liquid accelerants" attached to the explosive devices are also inside Apartment 10, the official said. "He placed other chemicals to enhance fire/thermal effect of IEDs," the official added about Holmes' apartment.

"He has a level of expertise, not crude," the official said.

About 100 officials were to converge at the apartment building at 1690 Paris Street. Federal personnel flown here from out of state include bomb technicians from the Bureau of Alcohol, Tobacco, Firearms and Explosives and Explosive Ordinance & Disposal specialists. Police evacuated five buildings Friday, including the one where Holmes lived, after he told them he had rigged his apartment with explosives.

"It is a very vexing problem how to enter that apartment safely. I personally have never seen anything like what the pictures show us is in there," Oates told reporters Friday night.

"I see an awful lot of wire, trip wires, jars full of ammunition, jars full of liquid and ... things that look like mortar rounds."

Holmes told police shortly after he was apprehended in the rear parking lot of the movie theater that he had rigged his apartment, Oates said.

Police arrived at Holmes' apartment to find techno music blaring from the bedroom, according to a law enforcement source, who spoke on condition of anonymity.

The music was on a timer and apparently started once he left for the movie theater, said the source, who was not authorized to release details of the investigation to the media.

Oates said it could take days to work through the apartment safely.

While authorities did not say how many residents were evacuated from nearby buildings, the number is estimated to be in the hundreds.

Authorities began Friday night to allow families in four of the five evacuated buildings to return to their residences to retrieve personal items, such as medication, identification cards and clothing.

A shelter was set up at Aurora Central High School for those forced from their apartments.