Investigators believe the gunman shot his mother at home, where he lived with her, and are researching the suspected gunman's writings, looking for any clues as to what might have precipitated one of the worst mass shootings in history. NBC's Pete Williams reports.

The weapons used in Friday’s shooting at Sandy Hook Elementary School in Newtown, Conn., were legally purchased and registered to Nancy Lanza, the mother of the gunman, Adam Lanza, two law enforcement officials told NBC News.

The gunman was clad in black and used two 9mm pistols to kill 20 small children and six adults at the school. It was unclear how many shots were fired there.

Two 9mm handguns, one made by Glock and the other by Sig Sauer, were recovered inside the school. An AR-15-type rifle also was found at the scene, but there were conflicting reports Friday night whether it had been used in the shooting.

In total, 28 people died in Friday's rampage, including the gunman, who was found at the scene, and a woman believed to be Nancy Lanza, found shot dead at a home in Newtown. She was a teacher.

Under Connecticut law, people under 21 are prohibited from purchasing or carrying handguns. Adam Lanza was 20.

The nonprofit Brady Campaign to Prevent Gun Violence ranks gun control laws in Connecticut and neighboring states New Jersey, New York and Massachusetts as the most stringent in the nation, after California.

Government officials 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.

Connecticut allows possession of assault rifles, except those with certain features, such as a fixed bayonet type lug, or a collapsible stock, according to attorney David Clough of Southbury, Conn.

Otherwise they are allowed, and like other rifles, easier to acquire than handguns.

Under Connecticut law, anyone 21 or older can purchase ammunition, Clough said.

The Associated Press, citing an unnamed official, reported that state police records show that Nancy Lanza had legally purchased five firearms, all registered in Connecticut, though the reported was not independently confirmed by NBC News. The AP later reported that authorities also recovered three other guns — a Henry repeating rifle, an Enfield rifle and a shotgun. It was not clear where those weapons were found.

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There have been several mass shootings in 2012 alone, and on Friday President Obama said politicians will need to come together to take action regardless of the politics. NBC's Tom Costello reports.

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