Speaking at an interfaith vigil in Newtown, Conn., Sunday night in memory of the 26 schoolchildren and teachers killed during a shooting massacre at an elementary school a few days earlier, U.S. President Barack Obama said he would use the power of his office to engage citizens and officials in the coming weeks to help prevent further tragedies.

"We can’t tolerate this anymore. These tragedies must end. And to end them, we must change," said Obama, speaking at Newtown High School, less than two kilometres away from Sandy Hook Elementary School, the site of Friday's shooting.

This is the fourth trip of Obama's presidency to a grieving city in the aftermath of a mass shooting. Most recently, last summer, Obama went to Aurora, Colo., to visit victims and families after a shooting rampage at a movie theatre in the Denver suburb left 12 dead.

Delivering his remarks following several members of the faith community and Connecticut Governor Dannel P. Malloy, Obama thanked the school's staff and first responders for their courage and offered condolences to the small Connecticut town, home to 27,000 people.

"I come to offer the love and prayers of a nation,” Obama said. "I can only hope it helps for you to know that you’re not alone in your grief, that our world, too, has been torn apart, that all across this land of ours, we have wept with you."

The president closed by reading aloud the names of the victims, saying "God has called them all home. For those of us who remain, let us find the strength to carry on and make our country worthy of their memory."

Mother shot four times in bed

Earlier today, Connecticut police confirmed the identity of the gunman linked to the massacre of 27 people — including 20 children, ages 6 and 7 — in Newtown, Conn., as Adam Lanza and verified that one of his victims as his mother, Nancy Lanza.

A Connecticut official said the 52-year-old mother was found dead in her pyjamas in bed in the home they shared, shot four times in the head with a .22-calibre rifle. The killer then went to the school Friday morning with guns he took from his mother, got inside by breaking a window and began blasting his way through the building.

The state medical examiner said the victims were shot multiple times.

State police spokesman Lt. Paul Vance said the majority of victims were killed by an "assault-type" rifle, a Bushmaster AR-15. Two guns were also recovered at the the school where the rampage occured — one of which was a handgun that the 20-year-old Lanza used to take his own life.

Police said Lanza shot himself in the head just as he heard police drawing near to the classroom where he was shooting helpless children.

Lanza also had more ammunition at the ready in the form of multiple, high-capacity clips each capable of holding 30 bullets.

"There was a lot of ammo, a lot of clips," Vance said. "Certainly a lot of lives were potentially saved."

Vance said a shotgun was also found in the vehicle he had been driving.

"We will determine every path those weapons took since they were manufactured," said Vance, who added that investigators were "successful" in the amount of material seized in their searches.

Vance said the next police news conference will take place Monday morning, likely at 9 a.m. local time.

Mourners, including children, squeezed into all three masses held at St. Rose of Lima Catholic church on Sunday.

The frayed nerves of the town's residents were tested when the church, located just 1.5 kilometres from the school, had to be evacuated around midday due to what churchgoers were told was bomb threat.

State troopers, police and ambulances briefly converged on the church. Police, with guns drawn, surrounded the rectory across the parking lot from the main church building. The situation quickly wrapped up. No other details were immediately known.

Vance said he "did not know the content of the threat" at the church.

Newtown, Conn., residents hold candles at a memorial for victims on the first Sunday following the mass shooting at Sandy Hook Elementary School on Friday. (Mario Tama/Getty Images)

Memorials dot Newtown's landscape. Eric Mueller, who lives down the street from the school, crafted 27 wooden angels and planted them in his front yard. Several shrines have been set up around the Catholic church with flowers, candles and plush toys. Memorials also ring the school where the attack happened Friday and a stone bridge over a river bears a giant, red cloth with the words "Pray for Newtown."

Amid the town's sorrow, stories of heroism have emerged over how teachers tried to save their young students from the gunman.

Witnesses say principal Dawn Hochsprung and school psychologist Mary Sherlach were shot and killed after lunging toward the assailant in an attempt to overpower him at Sandy Hook Elementary School.

"The principal and psychologist ran down the hall trying to intercept the gunman," CBC's Melissa Kent said, reporting from the town of 27,000 two days after the horrific shooting.

The vice principal also came out of the office when she heard shots and entered the hallway where she was wounded in the foot, forcing her to crawl back to the office. School therapist Diane Day stayed behind and hid.

“They didn’t think twice about confronting or seeing what was going on,” Day told the Wall Street Journal.

Police slam social media posts

What remains unclear is what motivated Lanza to carry out the horrific attack.

Vance has said in the past that key evidence in that regard had already been recovered but confirmed again on Sunday that investigators are nowhere close to releasing a summary of the possible motive.

"We have to have the whole picture first," he told reporters Sunday. "There are weeks worth of work left before we are to complete this."

Vance complained at length about "threatening and inaccurate" information circulating on social media websites and said those responsible "could be subject to arrest."

"There has been misinformation coming from people posing as the shooter in this case."

All he would say about the second crime scene is the shooting took place in "a singular section of the school, two classrooms and a hallway."

No survivors left in 1st classroom

The Hartford Courant newspaper says the first classroom Lanza entered was that of Grade One substitute teacher Lauren Rousseau where he shot her and all 14 of her students.

He next arrived at teacher Victoria Soto's classroom. Soto is believed to have hidden her 6- and 7-year old students in a classroom closet, the paper says.

Connecticut Chief Medical Examiner H. Wayne Carver talked of a very devastating set of injuries after the names of victims were released. (Jared Wickerham/Getty)

Six students who tried to flee were shot and killed. The gunman also killed Soto and another teacher who was in the room. Soto apparently tried to shield the children with her body, said one police officer .

“That is how she was found,” Jim Wiltsie told the Wall Street Journal. "Huddled with her children.”

The gunman's body was reportedly found near Soto's classroom.

Those killed included Ana Marquez-Greene, a six-year-old girl whose family lived in Winnipeg before they moved to Connecticut this year. Ana was the daughter of a professional jazz musician and she herself loved music. Ana's 9-year-old brother also was at the school, but escaped.

Teacher Janet Vollmer was teaching 19 five-year-old children when they heard popping sounds.

"My instinct was it wasn't good, so we kept them calm. We stayed in the room until there was banging on the door, which was the police and the troopers, and they had us exit the building," she told CNN.

While waiting for help, Vollmer locked the doors and put the blinds down. She then told the children to go to the back of the classroom where she read them a story.

With files from The Associated Press