Catherine Urso, of Newtown, said her college-age son knew the killer and remembered him for his alternative style. “He just said he was very thin, very remote and was one of the goths,” she said.

Adam Lanza attended Newtown High School, and several news clippings from recent years mention his name among the honor roll students.

Joshua Milas, who graduated from Newtown High in 2009 and belonged to the school technology club with him, said Adam Lanza was generally a happy person but that he hadn’t seen him in a few years.

“We would hang out, and he was a good kid. He was smart,” Joshua Milas said. “He was probably one of the smartest kids I know. He was probably a genius.”

An official who spoke on condition of anonymity said it was not clear that Adam Lanza had a job, and there was no indication of law enforcement interviews or search warrants at a place of business.

The mass shooting is one of the deadliest in U.S. history, and among school attacks is second in victims only to the 2007 Virginia Tech massacre, which left 33 people dead, including the gunman. Reaction was swift and emotional in Newtown, a picturesque New England community of 27,000 people, as well as across the country and around the world.

“It has to stop, these senseless deaths,” said Frank DeAngelis, principal of Colorado’s Columbine High School, where a massacre in 1999 killed 15 people.

In Washington, the Coalition to Stop Gun Violence organized a vigil at the White House, with some protesters chanting, “Today IS the day” to take steps to curb gun violence. In New York’s Times Square, a few dozen people held tea lights in plastic cups, with one woman holding a sign that read: “Take a moment and candle to remember the victims of the Newtown shooting.”

President Barack 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 at a White House news briefing. He paused for several seconds to keep his composure as he teared up and wiped an eye. Nearby, two aides cried and held hands.

Australian Prime Minister Julia Gillard described the attack as a “senseless and incomprehensible act of evil.”

“Like President Obama and his fellow Americans, our hearts too are broken,” Gillard said in a statement.

In Japan, where guns are severely restricted and there are extremely few gun-related crimes, the attack led the news two days before nationwide parliamentary elections. In China, which has seen several knife rampages at schools in recent years, the attack quickly consumed public discussion.

At the Newtown vigil, Anthony Bloss, whose three daughters survived, said they are doing better than he. “I’m numb. I’m completely numb,” he said.

The gunman entered the school through its front door, and authorities are looking into the possibility that he shattered glass next to it to get in, said Newtown Police Lt. George Sinko.

Panicked parents looking for their children raced to Sandy Hook, a kindergarten-through-fourth-grade school where police told youngsters to close their eyes as they were led from the building so that they wouldn’t see the blood and broken glass.

Schoolchildren — some crying, many looking frightened — were escorted through a parking lot in a line, hands on one another’s shoulders.

Robert Licata said his 6-year-old son was in class when the gunman burst in and shot the teacher. “That’s when my son grabbed a bunch of his friends and ran out the door,” he said. “He was very brave. He waited for his friends.”

He said the shooter didn’t utter a word.

Kaitlin Roig, a teacher at the school, said she implored her students to be quiet.