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Authorities ID gunman who killed 27 in elementary school massacre

NBC's Pete Williams has more information on a report that Connecticut school shooter Adam Lanza may have been involved in an altercation with staff members at Sandy Hook Elementary one day before the murders.

Undated photo confirmed by government officials to be Adam Lanza, who apparently killed himself after killing more than two dozen others, including 20 school children.

A day after the Newtown massacre, gunman Adam Lanza’s motive – and any personal demons – remained a mystery.

Lanza, 20, was identified by authorities as the black-clad killer who fatally shot his mother, gunned down 26 children and adults at Sandy Hook Elementary School, and then committed suicide on Friday. 

His older brother told authorities Lanza had a history of mental problems, but the nature of them was not clear. Former classmates remembered him as a brainy and quiet teen who sometimes wore a pocket protector.

Tim Arnone told Reuters that he first met Lanza at Sandy Hook and attended Newtown High School with him, where the two were members of a technology club. He said Lanza was "driven hard" to succeed academically by his parents, particularly his mother.

Nancy Lanza and her husband, Peter Lanza, divorced in 2008, according to public records. Peter Lanza could not immediately be reached for comment but has spoken to police.

Joshua Milas, who graduated from Newtown High School in 2009, told The Associated Press that 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." 

Catherine Urso, of Newtown, told the Associated Press her college-age son knew Lanza. "He just said he was very thin, very remote and was one of the Goths," she said.

Law enforcement officials initially told NBC News that the gunman was Lanza's brother, Ryan, and they had sent out a bulletin to local and federal law enforcement agencies to that effect.

But when authorities went to Ryan's home in Hoboken, N.J., to search it, they unexpectedly found him there.

Ryan told police he was not involved and that his brother has a history of mental health issues and might have had his ID even though they had not seen each other in two years, officials said.

A senior official later said that Ryan was nowhere near the shooting, was not believed to be involved, and was cooperating with the investigation.

Lanza's aunt, Marsha Lanza, of Crystal Lake, Ill., told the AP she was close with Adam Lanza's mother and sent her a Facebook message Friday morning asking how she was doing. Nancy Lanza never responded.

Marsha Lanza described Nancy Lanza as a good mother and kind-hearted. She said her husband saw Adam Lanza as recently as June and recalled nothing out of the ordinary about him.

Nancy Lanza’s mother was too distraught to speak when reached by phone at her home in Brooksville, Fla., the AP reported.

"I just don't know, and I can't make a comment right now," Dorothy Hanson, 78, said in a shaky voice as she started to cry.

NBC News Justice Correspondent Pete Williams contributed to this report.

Authorities are investigating why the alleged gunman would have killed his mother at home and then killed so many children. NBC's Pei-Sze Cheng reports.

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Michelle Mcloughlin / Reuters

The second deadliest school shooting in U.S. history sent crying children spilling into the school parking lot as frightened parents waited for word on their loved ones.