The alleged gunman behind the movie theater shooting in Colorado made his first court appearance Monday.

James Holmes, 24, showed little emotion as he was read his rights.

Holmes will be formally charged next Monday and could face the death penalty.

Colorado District Attorney Carol Chambers says the decision on whether to seek the death penalty could take months.

"Victims will be impacted by that decision in an enormous way for years if the death penalty is sought. That is a very long process that impacts their lives for years," Chambers said. "So they will want to have and we will want to get their input on that before we make any kind of decision on that."

Chambers adds it will likely be at least a year before Holmes stands trial.

Authorities say the former graduate student, who is being held in solitary confinement, is refusing to cooperate.

Investigators say it could take months to learn what prompted the horrific attack that killed 12 and injured 58 others at a midnight screening of the latest Batman film last Friday.

Authorities say they found a Batman mask inside Holmes' booby-trapped apartment.

University of Colorado officials are looking into whether the former neuroscience graduate student used his position to order materials to assemble the traps.

The U.S. Senate paid tribute to the victims of the Colorado movie theater shooting Monday.

Senators observed a moment of silence for the victims and Minority Leader Mitch McConnell read the names of those who were killed in the Senate chamber.

Meanwhile, in the wake of the Colorado massacre, Mayor Michael Bloomberg is keeping up his offensive in favor of stronger gun laws.

Appearing at a community health center in the East Village to tout his proposed ban on large sugary drinks, Bloomberg spoke to reporters on the issue of rationalizing the nation's gun laws which, for instance, require background checks when a gun is purchased in a store but not in a private sale.

Similar to his calls this past weekend, the mayor again directly challenged President Barack Obama and GOP presidential candidate Mitt Romney to take a firmer stance on the issue.

"Governor Romney signed a bill in Massachusetts prohibiting the sale of assault weapons and he spoke eloquently about it. Today he's not in favor of it. President of the United States Barack Obama campaigned four years ago on a platform of saying he was going to try to ban the sale of assault weapons and has done nothing since then. I think both of these people who want this job have an obligation not to duck the issue but to tell us what they're going to do, this is a scourge," Bloomberg said.

The mayor says some 48,000 Americans will be killed with illegal guns during the next president's term in office.