Assault rifle used during Sandy Hook massacre

(CBS News) NEWTON, Conn. - It's still unclear what -- if any -- connection suspected gunman Adam Lanza's mother had to Sandy Hook Elementary School, the scene of the mass murder on Friday. But we do know the weapons Adam Lanza used to kill his victims came from her home.

As new details emerge, the scope of the horror expands. Lanza apparently sprayed two classrooms at the school with relentless fire from a semi-automatic assault rifle.

It was a massacre, and most of the victims were first-graders. Autopsies on the bodies of the children reveal that many, if not all, had been shot multiple times.

"I only did seven of the autopsies," medical examiner Wayne Carver said. "The victims I had ranged from three to 11 wounds a piece, and I only saw two of them with close-range shooting."

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Investigators believe most of the bullets came from a Bushmaster .223 assault rifle. It was one of four guns Lanza took from the home he shared with his mother after he shot and killed her.

Sources say he left one gun in his car and forced his way into the school carrying the assault rifle in his hands and two semi-automatic pistols in the dark military-style cargo pants he was wearing.

Inside the school, he zeroed in on two classrooms, killing 20 children and six adults. One of them was the school principal, who sources say tried to stop the shooting by lunging at the gunman.

The spree ended when Lanza shot himself with one of the handguns.

Police have yet to find any journal or detailed notes Lanza may have left behind explaining his horrific actions. But Lt. Paul Vance said clues to the possible motive have been recovered in multiple searches.

"(We) did produce some very good evidence in this investigation that our investigators will be able to use and hopefully painting a complete picture as to how and more importantly why this occurred," Vance said.

It's not clear why Lanza targeted that elementary school. There were early reports on Friday that indicated his mother had been a teacher or an aide at Sandy Hook. Police have found no evidence she had any obvious connection to the school.

Police are also checking on a different report that maybe Lanza had been involved in an argument with staffers at the school the day before the shooting. Police have not confirmed that.