Attacker opens fire at Conn. school where mother worked; 26 killed, including 20 children

The shootings instantly brought to mind such tragedies as the Columbine High School massacre that killed 15 in 1999 and the July shootings at a movie theater in Aurora, Colo., that left 12 dead.

"You go to a movie theater in Aurora and all of a sudden your life is taken," Columbine Principal Frank DeAngelis said. "You're at a shopping mall in Portland, Ore., and your life is taken. This morning, when parents kissed their kids goodbye knowing that they are going to be home to celebrate the holiday season coming up, you don't expect this to happen."

He added: "It has to stop, these senseless deaths."

Obama's comments on the tragedy amounted to one of the most outwardly emotional moments of his presidency.

"The majority of those who died were children — beautiful little kids between the ages of 5 and 10 years old," Obama said.

He paused for several seconds to keep his composure as he teared up and wiped an eye. Nearby, two aides cried and held hands as they listened to Obama.

"They had their entire lives ahead of them — birthdays, graduations, wedding, kids of their own," Obama continued about the victims. "Among the fallen were also teachers, men and women who devoted their lives to helping our children."

Associated Press writers Jim Fitzgerald and Pat Eaton-Robb in Newtown, Bridget Murphy in Boston, Samantha Henry in Newark, N.J., Pete Yost in Washington and Michael Melia in Hartford contributed to this report, as did the AP News Research Center.