AURORA, Colo. — Federal and local authorities began disarming the booby-trapped apartment of a man arrested in the deadly mass shooting at a movie theater, neutralizing many of the sophisticated explosive devices on Saturday while trying to preserve evidence that might offer insight into the rampage.
Sergeant Cassidee Carlson of the Aurora Police Department said bomb specialists had eliminated the major threats in the apartment, making it safe to enter. But “there still remains all kinds of hazards inside the apartment,” she said. “We will remain here for hours to collect evidence and mitigate those hazards.”
Authorities disabled a second triggering device, she said, but the only way of knowing if all threats had been eliminated would be by entering the apartment.
The suspect, James Holmes, 24, is being held at the Arapahoe County Jail. He is scheduled to be arraigned Monday on charges stemming from the rampage that killed 12 people and wounded 58, in one of the worst mass shootings in US history.
Police had worked through the night to identify those killed and by Saturday morning they said they had notified all the families of victims, including some who had been holding out hope that those missing had been spared. There were still seven people hospitalized in critical condition, authorities said.
Led by the Bureau of Alcohol, Tobacco, Firearms, and Explosives, law enforcement agents secured the area around Holmes’s apartment, where they found a maze of wires and chemicals that they feared could be explosive. The apartment is a few miles from the multiplex where the shootings occurred.
Federal agents detonated one small explosive and disarmed another inside the apartment, including one that emits a shock wave and water, the Associated Press reported, citing a law enforcement official who spoke on condition of anonymity.
Holmes’s apartment appeared to have three types of explosives: jars filled with accelerants, chemicals that would explode when mixed together, and more than 30 ‘‘improvised grenades,’’ the official said.
The suspect had been a shy, awkward boy who once seemed quietly bound for big things, according to those who knew him. He was a science student from Southern California who won scholarships and internships, and he graduated at the top of his class at the University of California, Riverside.
Holmes moved to Colorado last year to enter a doctoral program in neuroscience, but he struggled through his first academic year at the University of Colorado Denver and had dropped out by this spring.
Neighbors described him as a solitary figure. They said that they heard loud music throbbing in his third-floor apartment, and often complained about it, or noticed a strange, purple light in the windows.
Initial spasms of shock and anger turned to raw, open sadness in Aurora on Saturday as police completed the task of informing families whose relatives were killed early Friday during a midnight screening of the new Batman movie, ‘‘The Dark Knight Rises.’’
The authorities did not immediately release to the public a list of the dead, but many family members came forward to identify the victims.
Makeshift memorials sprang up for the victims, including a 6-year-old girl, an aspiring sportscaster, and a man who had been celebrating his 27th birthday.
Many people took to Facebook and Twitter to express their grief.
The first victim publicly identified was Jessica Ghawi, an avid Twitter user who went by the handle @JessicaRedfield and had nearly 22,000 followers. As people took to the social media site to send their condolences, they also used the site strategically to control the tragedy’s resonance.
Many people started encouraging fellow Twitter users to tweet with the hashtag #RIPJessica, a request from the victim’s mother so that her daughter’s name would trend instead of the suspect’s.
Candlelight vigils were held across the city Friday night, and a local high school planned another memorial Saturday.
Residents in five buildings surrounding Holmes’s building were evacuated Friday. Sixteen of the evacuated were taken to a shelter at Central High School, where 12 others joined them late Friday night after an unrelated fire at an Aurora apartment building forced them from their homes.
“We are confident this is a safe area with the evacuations in place,’’ Sergeant Carlson said. Officials said they hoped to allow families back into their apartments by Monday.
Once the trip wires were rendered harmless, 30 aerial shells and about 30 other devices that had been observed inside the apartment were to be loaded into a sand truck and detonated at an unidentified facility, Carlson said.
Police then hoped to investigate the apartment like any other crime scene, she said.
Authorities also planned to make reverse 911 calls to alert members of the community about what was going on.
‘‘We don’t need to rush anything,’’ Carlson said, stressing the importance of preserving evidence. “There are still unknowns,’’ she added. “We are not sure about everything that is in there.’’
The authorities said that in the past 60 days, Holmes had legally purchased four guns at local gun shops — an AR-15 assault rifle, two Glock .40-caliber handguns, and a Remington 12-gauge shotgun — and acquired more than 6,000 rounds of assorted ammunition through the Internet.
The shooting stirred memories of the Columbine High School shooting, which took place about 20 miles away.
Why the suspect chose a movie theater to stage the assault has not been determined, or whether he intended some twisted, symbolic link to the film’s violent scenes.
The Batman movie, the last in the trilogy starring Christian Bale, opened worldwide Friday with midnight showings in the United States.
Police said that when he was arrested, Holmes said he compared himself to the Joker character in the Batman movies.
Local officers and firefighters were being helped by explosives specialists from the FBI and ATF. They faced a situation that the Aurora police chief, Dan Oates, said was unlike anything he had seen.
On Friday, he described an apartment littered with jars full of an unknown liquid, other jars full of ammunition, and yet more filled with what he said looked like mortar rounds. A series of wires ran between the jars, evidently set to blow up should they be disturbed. He said the intention appeared to be to to injure or kill police.
When the authorities arrested Holmes outside the movie theater where the shooting took place, he warned them that the apartment was rigged with explosives, police said.