Claire Davis, 17, lone victim of Colo. school shooting

Davis, a senior at Arapahoe High School, was sitting by the door with a friend when the shooter, 18-year-old Karl Pierson, entered the school with a shotgun and fired. (Via KUSA)

Grayson Robinson: "She was an innocent victim and I do believe that she was in the wrong place at the wrong time." (Via KMGH)

Arapahoe County Sheriff Grayson Robinson told reporters Davis was shot at point blank range and suffered severe head trauma. Although Davis was upgraded from serious to critical condition after surgery at a local hospital, her father told KMGH she's "not doing very well."

A day after the shooting, investigators are trying to pinpoint a motive as to why Pierson would want to shoot and possibly kill members of the Arapahoe High School community. But first, the "how."

"The shooter purchased the shotgun on Dec. 6 at a local retail outlet, The weapon was purchased legally." (Via CNN)

"It is our strong belief that he came to that school with that weapon and with multiple rounds and his intention was to utilize those multiple rounds." (Via KCNC)

Authorities believe Pierson arrived at the school wearing a bandolier and armed with his shotgun, a knife and three Molotov cocktails to exact revenge on his speech and debate coach for a previous confrontation. (Via Fox News)

Investigators say only 80 seconds elapsed between the time Pierson entered the school and the time he took his own life. In that time, The Denver Post writes, he fired his gun in Davis' face, ignited a Molotov cocktail that set bookshelves in the library on fire and committed suicide.

The Denver Post adds Pierson's mother was out of town when the shootings happened. Investigators searched Pierson's home and car but did not release what, if any, evidence was discovered.

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