NEWTOWN, CT (ABC News) - The FBI is in at least three states interviewing relatives and friends of the elementary school gunman who killed 20 children, seven adults and himself, trying to put together a better picture of the shooter and uncover any possible explanation for the massacre, ABC News has learned.
The authorities have fanned out to New Jersey, Connecticut and Massachusetts to interview relatives of Adam Lanza, 20, and his mother, who was one of Lanza's shooting victims.
The victims died Friday when Lanza invaded Sandy Hook Elementary School in Newtown, Conn., and sprayed staff and students with bullets, officials said. Lanza also was found dead in the school.
Lt. Paul Vance said 18 children died in the school and two more died later in a hospital.
Six adults also were slain, bringing the total to 26. Among them was the school's principal, Dawn Hochsprung, multiple sources told ABC News. Another adult victim was teacher Vicki Soto, her cousin confirmed.
In addition to the casualties at the school, Lanza's mother, Nancy Lanza, was killed in her home, federal and state sources told ABC News.
According to sources, Lanza shot his mother in the face, then left his house armed with at least two semi-automatic handguns, a Glock and a Sig Sauer, and a semi-automatic rifle. He was also wearing a bulletproof vest.
Lanza then drove to the elementary school and continued his rampage, authorities said.
It appeared that Lanza died from what was believed to be a self-inflicted gunshot wound. The rifle was found in his car.
"Evil visited this community today," Gov. Dan Malloy said at a news conference Friday evening.
In the early confusion surrounding the investigation, federal sources initially identified the suspect as Adam's older brother Ryan Lanza, 24. Identification belonging to Ryan Lanza was found at the shooting scene, federal sources told ABC News.
Ryan Lanza soon took to Facebook to say he was alive and not responsible for the shooting. He later was questioned by police.
During the rampage, first-grade teacher Kaitlin Roig, 29, locked her 14 students in a class bathroom and listened to "tons of shooting" until police came to help.
"It was horrific," Roig said. "I thought we were going to die."
She said that the terrified kids were saying, "I just want Christmas. ... I don't want to die. I just want to have Christmas."
A tearful President Obama said Friday that there was "not a parent in America who doesn't feel the overwhelming grief that I do."
The president had to pause to compose himself after saying these were "beautiful little kids between the ages of 5 and 10."
As he continued with his statement, Obama wiped away tears from each eye. He has ordered flags flown as half staff.
It is the second worst mass shooting in U.S. history, exceeded only by the Virginia Tech shooting in 2007 when 32 were killed before the shooter turned the gun on himself. The carnage in Connecticut exceeded the 1999 Columbine High School shooting in which 13 died and 24 were injured.
Friday's shooting came three days after masked gunman Jacob Roberts opened fire in a busy Oregon mall, killing two before turning the gun on himself.
The Connecticut shooting occurred at the Sandy Hook Elementary School, which includes 450 students in grades K-4. The town is located about 12 miles east of Danbury, Conn.
The massacre prompted the town of Newtown to lock down all its schools and draw SWAT teams to the school, authorities said.
State Police received the first 911 call at 9:41 a.m. and immediately began sending emergency units from the western part of the state. Initial 911 calls said multiple students were trapped in a classroom, possibly with a gunman, according to a Connecticut State Police source.
Vance said on-duty and off-duty officers swarmed to the school and quickly checked "every door, every crack, every crevice" in the building looking for the gunman and evacuating children.
PHOTO: People gather outside a fire house near the Sandy Hook Elementary School following a shooting that left at least 27 people dead, many of the young children, in Newtown, Connecticut, on December 14, 2012.
Soon, state police from across western Connecticut would be there. And they would be joined by FBI SWAT and evidence teams as well as members of the federal Bureau of Alcohol Tobacco and Firearms.
A photo from the scene showed a line of distressed children being led out of the school.
Three patients were taken to Danbury Hospital, which also went on lockdown, according to the hospital's Facebook page.
ABC News' Michael S. James contributed to this report.