NEWTOWN, Conn. - The weapon "utilized most of the time" during Friday's Connecticut school shooting was a Bushmaster AR-15 "assault-type weapon," Connecticut State Police Lt. J. Paul Vance said Sunday afternoon.
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Adam Lanza fired "hundreds of bullets" from "multiple magazines" from the Bushmaster during the massacre, Vance said. Lanza killed himself with a handgun.
Connecticut State Police also positively identified Lanza as the gunman for the first time during the Sunday news conference.
In a town still numb from the inexplicable massacre of children, investigators were interviewing witnesses and searching for clues Sunday.
"Our people are talking with everybody slowly but surely, but methodically, too," Vance told reporters. "This is something where people's hearts are broken, as we all well know. And we have to be sensitive."
Questions and anguish abound two days after police said Lanza shot his mother before killing 20 students and six adults at a Connecticut elementary school. He apparently turned his weapon on himself, silencing any way for the world to understand fully what was in his mind.
As the community grieves, relatives of the victims will meet with President Barack Obama on Sunday when he visits the city.
Here's the latest on the massacre at Sandy Hook Elementary School in Newtown:
The shooter used a gun to force his way into the building, Connecticut Gov. Dan Malloy said Sunday.
"What we know is he shot his way into the building. He was not buzzed in," Malloy said. "He penetrated the building by literally shooting an entrance into the building. That's what an assault weapon can do for you."
Investigators believe the gunman opened fire in two classrooms at the school, then shot himself as authorities entered the building, Malloy told ABC's "This Week."
"We surmise that it was during the second classroom episode that he heard responders coming and apparently at that decided to take his own life," he said.
Authorities still have many witnesses they plan to interview about the shooting, Vance said, and they're analyzing evidence they've collected. The investigation could take weeks, he said.
As authorities continued their search for evidence, a new investigation was starting Sunday.
Inaccurate information about the elementary school shooting is spreading on social media, and authorities could prosecute those responsible, Vance said.
"There has been misinformation from people posing as the shooter in this case, posing using other IDs, mimicking this crime and crime scene and criminal activity that took place in this community," he said. "There's been some things in somewhat of a threatening manner."
Vance did not provide details about the threats or specify whether authorities had questioned or arrested anyone in connection with them.
"Prosecution will take place when people who are perpetrating this information are identified," he said.
All the victims died from gunshot wounds and were struck multiple times, said H. Wayne Carver II, Connecticut's chief medical examiner. Their deaths were classified as homicides.
"This probably is the worst I have seen or the worst that I know of any of my colleagues having seen," Carver told reporters.
All 20 of the slain children were either 6 or 7 years old.
Among those killed was 6-year-old Emilie Parker. Her father struggled to hold back tears while recalling the life cut far too short.
"As the deep pain begins to settle into our hearts, we find comfort reflecting on the incredible person that Emilie was and how many lives that she was able to touch in her short time here on earth," Robbie Parker told reporters.
"She loved to use her talents to touch the lives of everyone that she came in contact with," he added. "She always carried around her markers and pencils so she never missed an opportunity to draw a picture or make a card for those around her."
Robbie Parker also offered his condolences to all the families affected.
"This includes the family of the shooter," he said. "I can't imagine how hard this experience must be for you, and I want you to know that our family, and our love and support goes out to you as well."
Six adults were also killed in the school rampage, including principal Dawn Hochsprung, school psychologist Mary Sherlach, first-grade teacher Vicki Soto and substitute teacher Lauren Rousseau.
Hochsprung recently oversaw the installation of a new security system requiring every visitor to ring the front entrance's doorbell after the school doors locked at 9:30 a.m.
Authorities said the first emergency call about the shooting came in at "approximately" 9:30 a.m. Friday.
The few relatives and acquaintances who have spoken out about Adam Lanza were at a loss to explain how this could have happened.
An aunt and a former classmate described him as very intelligent and quiet. He had no known criminal record.
His father, Peter Lanza, released a statement Saturday expressing condolences to the families of victims.
"Our family is grieving along with all those who have been affected by this enormous tragedy. No words can truly express how heartbroken we are," the statement read. "We are in a state of disbelief and trying to find whatever answers we can."
The gunman's father and brother have been questioned by authorities, law enforcement officers said.
As a teenager, the shooter often sat alone in the back of the school bus, his former bus driver said.
"He didn't sit with the other kids and didn't seem to have any friends," said Marsha Moskowitz, 52, who said she drove Lanza to school for three years starting when he was age 13.
Lanza was one of the older kids on the bus and did little to interact with the others, she said. "He was quiet, a very shy and reserved kid."
The gun control debate
The deadly shooting that shattered this quiet New England town also reignited the ongoing debate about gun laws in America.
Democratic Sen. Dianne Feinstein of California said Sunday that she will introduce a bill next month in the Senate to place a ban on assault weapons.
"It will ban the sale, the transfer, the importation, and the possession. Not retroactively, but prospectively. It will ban the same for big clips, drums or strips of more than 10 bullets," Feinstein said on NBC's "Meet the Press." "There will be a bill."
Adam Lanza was found dead next to three guns -- the semiautomatic .223-caliber rifle made by Bushmaster and two handguns made by Glock and Sig Sauer, a law enforcement source told CNN. All belonged to his mother.
Carver, who performed autopsies on seven of the victims, said the wounds he knew about were caused by a "long weapon" and that the rifle was the primary weapon used.
Adam's mother, Nancy Lanza, was a gun collector and recently showed off a newly bought rifle to fellow Newtown resident Dan Holmes, who owns a landscaping business in the town.
Besides the three weapons found at the school, the shooter also had access to at least three more guns, a law enforcement source said.
On Sunday, Connecticut's governor said federal officials need to do more to regulate guns.
"These are assault weapons. You don't hunt deer with these things. ... One can only hope that we can find a way to limit these weapons that really have one purpose," Malloy said.
The massacre in Newtown is the second-deadliest school shooting in U.S. history, behind the 2007 Virginia Tech shooting spree that left 32 dead.
"Stuff like this does not happen in Newtown," said Renee Burn, a teacher at another school in the town, which is roughly 75 miles northeast of New York.
Until Friday, only one homicide in 10 years had been reported in the upscale community of expansive homes surrounded by woods, where many residents commute to jobs in Manhattan and the nearby Connecticut cities of Stamford and Hartford.
The shooting wounded the entire community, said Sen. Richard Blumenthal, D-Connecticut, who has met with victims' families and watched devastated parents learn their children had been slain last week.
"I don't think I will ever forget the cries of grief and pain that I saw at the firehouse on that day," he said, "as a parent, as a person, just the unspeakable sadness that pervades this town still, and will go on for quite some time."