NATIONAL NEWS (CNN) — Investigators completed the first of a planned three-step operation Saturday intended to allow their entry into the booby-trapped apartment of movie-theater shooting suspect James E. Holmes.

A trip wire and an incendiary device have both been defeated, Public Information Officer Sgt. Cassidee Carlson told reporters. "This trip wire was set up to clearly detonate when somebody entered the apartment, and it was set up to kill that person," she said. "That could have been a police officer executing a search warrant. This is some serious stuff our team is dealing with."

The team of dozens of federal, state and local investigators was reassessing how to proceed, she said. "There are other devices inside."

The next phase may include the "controlled detonation" of another triggering mechanism, she said.

Fire officials were on standby, she said.

Investigators were planning to use a robot to disarm trip wires linked to explosives, and then use that same robot to remotely remove the improvised explosive devices, a law enforcement official with direct knowledge of the operation told CNN. It was also possible one of the bomb experts on site would put on protective gear and go inside the apartment, the official added.

Carlson did not say whether that occurred.

It was not clear where all the explosives were located, though many have been seen in the living area with circuitry reaching into the kitchen, the official said.

One of the incendiary devices appears to be improvised napalm and others appear to be mixtures that, if combined with other materials, could cause an explosion, the official said.

Approximately 30 aerial shells are in the 850 square foot apartment, Carlson said. They will be placed on sand trucks and taken to a disposal site for controlled detonation, she said.

"During any of these phases, and as this day goes on, again, there may be controlled detonations," she said, adding that reverse 911 calls would alert the general public prior to any blasts.

Asked what timeline authorities were expecting to follow, she said, "There is no timeline. I can't give you an endtime. We're hoping to get in there within the next hour."

But, she added, "We have no idea how long any of this is going to take."

Officials were hoping to avoid detonations, she added. "Anything that's in there we're going to be using as evidence so we're going to be very cautious in how we deal with things."

"Jars of black powder" and what appear to be "liquid accelerants" attached to the explosive devices are also inside Apartment 10, another law enforcement 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 called in to oversee the entrance into Apartment 10 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," Police Chief Daniel 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."

Shortly after police apprehended Holmes in the rear parking lot of the Century Aurora 16 movie complex, where dozens of people had been shot, he told them 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 Friday that 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.