AURORA, Colo. -- The Colorado shooting suspect planned the rampage that killed 12 midnight moviegoers with "calculation and deliberation," police said yesterday, receiving deliveries for months that authorities believe armed him for battle and were used to rig his apartment with dozens of bombs.

Authorities yesterday were still working to clear dangerous explosive materials from inside James Holmes' suburban Denver apartment a day after, police said, he opened fire and set off gas canisters in a suburban theater minutes into the premiere of the Batman film "The Dark Knight Rises." At least 70 people were wounded.

His apartment was rigged with jars of liquids, explosives and chemicals that were booby-trapped to kill "whoever entered it," Aurora Police Chief Dan Oates said, noting it probably would have been one of his officers.

"You think we're angry? We sure as hell are angry," Oates said.

Authorities wouldn't discuss a motive for one of the deadliest mass shootings in recent U.S. history, as makeshift memorials for the victims sprang up and relatives began to publicly mourn their loved ones.

Meanwhile, the White House said President Barack Obama would be in Colorado Sunday to visit with victims of the shooting and their families.

Holmes had recently withdrawn from a competitive graduate program in neuroscience. Neighbors and former classmates in California have said he was a smart loner who said little.

But he had apparently prepared the attack at the Aurora theater well in advance, receiving multiple deliveries by mail for four months to his home and school and buying thousands of rounds of ammunition on the Internet, Oates said.

"What we're seeing here is evidence of some calculation and deliberation," Oates added.

Federal authorities detonated one small explosive of their own and disarmed others inside Holmes' apartment after sending in a robot to circumvent a trip wire, FBI Special Agent James Yacone said.

Holmes, 24, was in a county detention facility yesterday, held without bond on suspicion of multiple counts of first-degree murder. He was set for an initial hearing on Monday and had been appointed a public defender, authorities said.

His lawyer is James O'Connor, head of the public defender's office that covers the sprawling 18th Judicial District, from suburban Denver to the eastern Colorado plains. He did not immediately return a call seeking comment.

Arapahoe County Sheriff Grayson Robinson said his office is not releasing a photo or mug shot of Holmes at the request of the Aurora Police Department because the case is still under investigation.

Stories of the dead began to emerge, including that of a 6-year-old girl, and of a man who died on his 27th birthday and a day before his anniversary. Families grieved and waited at hospitals, which reported at least seven wounded still in critical condition yesterday and others with injuries that probably were permanent.

The Batman movie, the last in the trilogy starring Christian Bale, opened worldwide Friday with midnight showings in the United States. The plot has the villain Bane facing Bale's Caped Crusader with a nuclear weapon that could destroy fictional Gotham City.

After excelling at the University of California-Riverside, Holmes was withdrawing from a neuroscience PhD program at the University of Colorado-Denver for unknown reasons.

First-year students must take a three-part exam at the end of the academic year to move on in the program, university spokeswoman Jacque Montgomery said yesterday. Montgomery did not know whether Holmes had taken the exam.

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