Early Thursday morning, a school bus carrying students from Sandy Hook Elementary headed to their new school. Timothy A. Clary/AFP/Getty Images hide caption

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After the attack: Balloons hung from the Sandy Hook Elementary School sign on Dec. 15. On Dec. 14, six adults and 20 children were killed there before the gunman took his own life. Shannon Stapleton/Reuters /Landov hide caption

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Mourners put decorations on a Christmas tree, part of a memorial in Newtown, Conn. Holiday greetings, toys and cards have flowed into the town, and some residents say the community feels closer-knit since the shooting. Zhang Chuanshi /Xinhua/Landov hide caption

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Christmas stockings with the names of shooting victims hang from a railing in the Sandy Hook village of Newtown, Conn. Julio Cortez/AP hide caption

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Police Lt. Ray Mesek registers a rifle at a gun buyback event on Saturday in Bridgeport, Conn. Spencer Platt/Getty Images hide caption

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A school bus drives past a welcome sign near the Chalk Hill Middle School in Monroe, Conn. Students from Sandy Hook Elementary in neighboring Newtown will attend the school in January. Lucas Jackson/Reuters/Landov hide caption

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A person's DNA can say a lot about a person, but not why someone has committed a horrific crime like mass murder. iStockphoto.com hide caption

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Stuffed animals and flowers at a makeshift memorial near the entrance to the grounds of Sandy Hook Elementary School. Brendan Smialowski /AFP/Getty Images hide caption

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A Sig Sauer handgun on sale at a shop in Tucker, Ga. Erik S. Lesser /EPA /LANDOV hide caption

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A woman and child earlier this week at a makeshift memorial in Newtown, Conn. Shannon Stapleton /Reuters /Landov hide caption

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A child peers through firefighters standing as the procession heads to the cemetery outside the funeral for school shooting victim Daniel Barden at St. Rose of Lima Catholic Church in Newtown, Conn., Charles Krupa/AP hide caption

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