President Barack Obama suspended campaigning and said the nation should take a day for reflection in the wake of the "senseless" mass shooting in Colorado.
"We may never understand what leads anybody to terrorize their fellow human beings like this," Obama said in Fort Myers, Florida. "Such violence, such evil is senseless. It's beyond reason."
At least 12 people were killed and 50 injured when a gunman opened fire during a midnight showing of the new Batman movie, "The Dark Knight Rises," federal and local authorities said. A suspect is in custody.
Obama was informed of the shooting at 5:26 a.m. by his homeland security adviser, John Brennan, and later got a briefing from FBI Director Robert Mueller, White House press secretary Jay Carney told reporters traveling with the president in Florida. Obama also spoke with the mayor of Aurora and the governor of the state.
There is no indication that the shooting was linked to any terrorist group, Carney said.
Upon learning of the tragedy, the president said his first reaction was that of a parent.
"My daughters go to the movies," he said. "What if Malia and Sasha had been at the theater?"
He said he and first lady Michelle Obama will "hug our girls a little tighter tonight."
"If there's anything to take away from this tragedy, it's a reminder that life is very fragile," Obama said. "Our time here is limited and it is precious."
The president said federal law enforcement authorities will do whatever is necessary to assist Colorado officials.
The president was in Florida as part of a two-day campaign swing. He canceled later scheduled events and will to return to Washington, campaign spokeswoman Jen Psaki told reporters. The campaign is asking television stations in Colorado to suspend "contrast advertising" in the wake of the shooting.
Republican presidential candidate Mitt Romney said he and his wife, Ann, "are deeply saddened by the news of the senseless violence" in the Denver suburb.
The Romney campaign also canceled events and is pulling advertising in Colorado.
"There are going to be other days for politics," Obama said. "This, I think, is a day for prayer and reflection."
The victims were "mothers and fathers, husbands and wives, sisters and brothers," Obama said. "They had hopes for the future and they had dreams that were not yet fulfilled."