"Tomorrow evening, the president will travel to Newtown, Conn., to meet with the families of those who were lost and thank first-responders," the office of press secretary Jay Carney said in a statement. "The president will also speak at an interfaith vigil for families of the victims as well as families from Sandy Hook Elementary School scheduled for 7 p.m. EST."
A law enforcement source told CNN the shooter, Adam Lanza, 20, had gotten into a disagreement Thursday with four adults at Sandy Hook Elementary School. Three of those adults were among the six adults and 20 children killed Friday, CNN said.
The state's chief medical examiner said Saturday all of the children were shot multiple times, all apparently with a rifle, The New York Times reported.
"This is a very devastating set of injuries," Dr. H. Wayne Carver II, the chief medical examiner, was quoted as saying. If they suffered, he said, it was "not for very long."
Parents were shown photos of their children for identification purposes, he said.
The victims ranged in age from 6 to 56. The children -- 12 girls and eight boys -- were all first-graders between the ages of 6 and 7.
The children were identified as: Charlotte Bacon, 6, Daniel Barden, 7, Olivia Engel, 6, Josephine Gay, 7, Ana M. Marquez-Greene, 6, Dylan Hockley, 6, Madeleine F. Hsu, 6, Catherine V. Hubbard, 6, Chase Kowalski, 7, Jesse Lewis, 6, James Mattioli, 6, Grace McDonnell, 7, Emilie Parker, 6, Jack Pinto, 6, Noah Pozner, 6, Caroline Previdi, 6, Jessica Rekos, 6, Avielle Richman, 6, Benjamin Wheeler, 6, and Allison N. Wyatt, 6.
The adults killed were: Rachel Davino, 29, Dawn Hochsprung, 47, Anne Marie Murphy, 52, Lauren Rousseau, 30, Mary Sherlach, 56, and Victoria Soto, 27.
Investigators spent Saturday poring over the school.
"The detectives will certainly analyze everything and put a complete picture together of the evidence that they did obtain, and we're hopeful -- we're hopeful -- that it will paint a complete picture as to how and why this entire unfortunate incidence occurred," CNN quoted Lt. J. Paul Vance of the State Police as saying.
Authorities say they believe Lanza shot and killed his mother Nancy Lanza at the Newtown home they shared before heading to the school, where Vance said the young shooter "forced his way" into the building Friday morning and opened fire. Lanza ended the rampage by taking his own life, police said.
Vance said investigators had spoken with the one unidentified wounded adult who survived the rampage. The woman was shot in the foot.
"She has been treated and she'll be instrumental in this investigation, as I'm sure you can understand," Vance said.
Vance said at a morning news briefing that detectives likely would remain at the crime scene for the next couple of days.
Lanza may have had access to at least five guns, a law enforcement official told CNN Saturday. Officials said previously three weapons were recovered from the school -- a semi-automatic .223-caliber rifle in a car in the school parking lot, and two pistols found by Lanza's body.
CNN reported a member of Lanza's family told investigators he had a form of autism.
A kindergarten teacher at Sandy Hook said Lanza's mother, Nancy Lanza, was not a teacher at the school, despite earlier reports that she was.
Former classmates described the shooter as a shy child and teenager.
Kateleen Soy told the Hartford Courant she knew Lanza as a seventh-grader at St. Rose of Lima School in Newtown and later saw him in the halls at Newtown High School. She described him as "really painfully shy."
"I wanted people to know he wasn't always a monster," Soy said. "He became one, but he wasn't always that way."
Andrew Lapple said he was on the same Little League team and also sat next to Lanza in homeroom at the high school. He called Lanza a "tech-geek" with little talent for baseball.
"He was always carrying around his laptop holding onto it real tight," Lapple said. "He walked down the halls against the wall almost like he was afraid of people. He was definitely kind of strange, but you'd never think he'd do something like this."
The Newtown shooting is believed to be the second-most deadly school shooting in U.S. history. In 2007, a student at Virginia Tech, Seung-hui Cho, killed 32 students and teachers and then killed himself.