(CNN) -- The man accused of opening fire in a crowded Colorado movie theater left a trail of evidence that police say suggests the rampage was part of a calculated plan that included killing anyone who tried to learn more about him in the aftermath of the attack.
The revelations raised new questions about a possible motive in the attack in the suburban Denver community of Aurora that shocked a nation. President Barack Obama was scheduled Sunday to meet with victims' families and get an update on the investigation.
Authorities have said little about what they believe was the motive of suspect James E. Holmes, though investigators say there is evidence planning was under way for up to two months before the early Friday morning attack that left 12 dead and 58 wounded at the theater.
Holmes, 24, is being held in connection with the rampage at the theater and the subsequent discovery of his booby-trapped apartment, which authorities believe he rigged before leaving for the Century Aurora 16 multiplex.
Holmes received a high volume of deliveries over the past four months to both his home and work addresses, which police believe begins to explain how he got his hands on some of the materials used in the attack and those found at his apartment, said Aurora Police Chief Daniel Oates.
"What we're seeing here is evidence of, I think, some calculation and deliberation," Oates said.
"We have the evidence of a deliberative process to commit this assault, and we have the evidence of a deliberative process in his mind to attack whoever opened the door of his apartment."
Police gained access Saturday to Holmes' apartment after intentionally detonating two rigged explosives.
Technicians, with the help of a robot, worked to handle traps, wires and possible explosive and incendiary devices, Jim Yacone, a special agent with the FBI, told reporters Saturday.
The operation proceeded with an eye toward preserving evidence, all of which will be sent to an FBI lab in Quantico, Virginia, Yacone said.
Hundreds of residents were evacuated from five buildings, including the modest, three-story brick building where Holmes told police he had rigged his top-floor, one-bedroom apartment with explosives. All occupants except those who live in the suspect's building were allowed to return home Saturday night, police said.
While the threat to the apartment building Holmes lived was eliminated Saturday, Oates said the residences were being kept out at least until Sunday as investigators work "to preserve evidence."
By early Sunday morning, at least 26 people remained hospitalized -- nine in critical condition -- in five area hospitals.
Aurora's residents, meanwhile, were grappling with the aftermath of the carnage.
President Obama was due to meet with the injured and the families of those killed Sunday night in Aurora, where the city was planning a vigil that was expected to draw various public officials.
Oates said the Century 16 multiplex would remain shuttered at least until Wednesday to give police time to complete the investigation inside and allow the suspect's defense team access by Tuesday.
Holmes, who is being held in Arapahoe County Jail, is scheduled to appear in court on Monday morning. The court file was sealed, according to a court order.
Investigators have said little about what may have led the suspect to open fire during "The Dark Knight Rises."
Witnesses described the gunman as wearing a gas mask that concealed much of his face and head.
Holmes' hair had been dyed red, and he told police when he was arrested in the rear parking lot of the theater minutes after the rampage that he was "the Joker," according to a federal law enforcement source with knowledge of the investigation. The source was not authorized to release details to the media.
The Joker has long been a fixture in Batman comics and was famously portrayed by Heath Ledger in 2008's "The Dark Knight," the predecessor to "The Dark Knight Rises."
Oates has declined to release details about Holmes' appearance other than to describe what he was wearing: a ballistic helmet and protective gear for his legs, throat and groin, black gloves and a gas mask.
He also said he would not release the booking photo "for investigative reasons."
CNN's Tom Watkins, Dana Ford, Carol Cratty, Ed Lavandera, Susan Candiotti, Joe Sutton, Mike Brooks, Sarah Aarthun and Jim Spellman contributed to this report.
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