Authorities say they believe major threats have been eliminated from the booby-trapped apartment of the suspect in the movie theatre shootings in Aurora, Colorado, predicting that residents of the complex will likely be able to return home Sunday.

On Saturday morning, Colorado police disarmed the trip wire and an explosive device that would have been triggered by opening the front door.

They then detonated an explosive device in the apartment, causing a small bang and blowing out what remained of the apartment's main window and its frame.

A law enforcement official, speaking on condition of anonymity to The Associated Press, said the apartment appears to have three types of explosives: jars filled with accelerants, chemicals that would explode when mixed together and more than 30 "improvised grenades" that resemble commercially available aerial fireworks shells.

James Holmes, 24, is the suspect in a shooting attack that killed 12 people in a suburb of Denver. (The University of Colorado/Reuters)

Officials say chemists are also going to be on hand for the delicate search, which involves bomb technicians and firefighters.

Aurora Police Chief Dan Oates said officials have tracked many packages that the suspect had delivered to his residence and office over a four-month period. Parcels that officials believe likely contained ammunition and bomb-making materials.

He added that police have received 84 leads through a tip line set up for the investigation.

Oates said he expected to "hand back" the theatre to its owners on Wednesday. The police chief expressed anger that the suspect had created a trap in his apartment that "was designed to kill whoever entered, [and] that likely would have been a police officer."

Authorities are hoping to find a motive for the killings, and a safe way to reach clues inside the suspect's apartment, which is rigged with an elaborate booby trap.

Paramedics remain on standby as officials positioned vehicles and personnel around the apartment building.

Twelve people died and 58 were injured in the attack early Friday, a few of those not by gunfire but in the chaos that ensued as the audience tried to flee the smoke-filled theatre, authorities said. Among the wounded, 11 were listed in critical condition.

Gov. John Hickenlooper praised first responders in an afternoon news conference.

"What a miracle it wasn't worse," he said.

Hickenlooper noted ambulances were at the theatre within two minutes of getting the emergency call. The governor went on to laud police, doctors as well as the team involved in disarming the devices in the apartment — the FBI and the Alcohol, Tobacco and Firearms division (ATF).

Six-year-old among dead

The deceased victims, all named Saturday, included 23-year-old Micayla Medek. The family took the news hard, but knowing her fate after waiting without word brought them some peace, said Anita Busch, the cousin of Medek's father.

"I hope this evil act, that this evil man doesn't shake people's faith in God," she said.

Besides Medek, six-year-old Veronica Moser, whose mother remains in hospital, and Jessica Ghawi were among those killed, as well as Alex Sullivan, who was out celebrating his 27th birthday.

Police grimly went door to door late Friday with a list of the victims killed in the worst mass shooting in the U.S. in recent years, notifying families who had held out anxious hope that their loved ones had been spared inside the packed theatre near Denver.

Hours after the shootings, it remained unclear what might have driven the gunman to fire round after round at the unsuspecting audience watching The Dark Knight Rises. Police Chief Oates said the assailant used a military-style semi-automatic rifle, a shotgun and a pistol that he had bought at local gun stores within the last two months. He also recently purchased 6,000 rounds of ammunition over the internet, the chief said.

The suspect in the killings has been identified as 24-year-old James Holmes. His stellar academic record, apparent shy demeanour and lack of a criminal background made it even more difficult to fathom that he was behind the attack.

It also wasn't known why he might have chosen a movie theatre to stage an assault, or whether he intended some twisted, symbolic link to the film itself.

The new Batman movie, the last in the trilogy starring Christian Bale, opened worldwide Friday with midnight showings in the U.S. The plot has the villain Bane facing Bale's caped crusader with a nuclear weapon that could destroy all of fictional Gotham.

'Deranged individual'

Near the entrance to the Aurora theatre's parking lot, a makeshift memorial of 12 candles sat in a row near piles of flowers. Up the hill, about 20 pastors led an emotional vigil for about 350 people, some hugging and crying. A sign read, "7/20. Gone Not Forgotten."

'When is this going to become a hostage situation?'—Movie goer Tanner Coon

A federal law enforcement official said Holmes bought a ticket to The Dark Knight Rises, went into the theatre as part of the crowd and propped open an exit door as the movie was playing. The suspect then donned protective ballistic gear and opened fire, the official said, speaking on condition of anonymity to discuss the ongoing investigation.

Authorities said he hit scores of people, picking off people who tried to flee. At least one person was struck in an adjacent theatre by gunfire that went through the wall. Adding to the terror and chaos were gas canisters thrown by the suspect that filled the packed suburban Denver theatre with smoke.

Tanner Coon, a 17-year-old Aurora resident who was watching the film with two friends, said he first thought the gunshots were firecrackers. When he realized what was happening, he ducked between the seats and waited for the shooter to say what he wanted.

A memorial site for victims has been created behind the theatre. (Shannon Stapleton/Reuters)

"When is he going to start telling us what to do? When is this going to become a hostage situation?" Coon said.

When the firing ended, Coon said he started running up the row but slipped in blood and fell on top of a woman who was lying on the ground. He tried shaking her, he said, but she didn't respond, so he left her behind and ran out of the theatre.

Police swarmed theatre

Within minutes, frantic 911 calls brought some 200 police officers, ambulances and emergency crews to the theatre. Holmes was captured in the parking lot.

Kaitlyn Fonzi, a graduate student at University Hospital who lives in the apartment below, said she heard loud music coming from that unit apartment. She went upstairs 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.

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 shaken to learn later that the apartment was booby trapped.

"I'm concerned if I had opened the door, I would have set it off," she said.

The shooting was the worst in the U.S. since the Nov. 5, 2009, attack at Fort Hood, Texas. An Army psychiatrist was charged with killing 13 soldiers and civilians and wounding more than two dozen others. It was the deadliest in Colorado since the 1999 attack at Columbine High School, where two students killed 12 classmates and a teacher and wounded 26 others before killing themselves.

Holmes had enrolled last year in a neuroscience Ph.D. program at the University of Colorado-Denver, though he left the program last month for unknown reasons. In academic achievement, "he was at the top of the top," recalled Timothy P. White, chancellor at the University of California, Riverside, where Holmes earned his undergraduate degree before attending the Denver school.

Those who knew Holmes described him as a shy, intelligent person raised in California by parents who were active in their well-to-do suburban neighborhood in San Diego. Holmes played soccer at Westview High School and ran cross-country before going to college.

Police released a statement from his family Friday that said, "Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved."

According to officials Holmes is being held in solitary confinement for "his own protection" at the Arapahoe County Jail.