CENTENNIAL, Colo. – The student who opened fire at his suburban Denver high school last week apparently planned to attack at least five different areas, investigators said Tuesday.

Letters and numbers corresponding to the locations of the Arapahoe High School library and four adjacent classrooms were written in indelible marker on Karl Pierson’s arm, and investigators believed he planned to target those spots, Arapahoe County Sheriff Grayson Robinson said in a statement.

Additional Photos

Arapahoe students leave flowers and other items at a makeshift tribute site three days after a shooting attack at Arapahoe High School in Centennial, Colo., Monday, Dec. 16, 2013. They are from left, Hannah Eddy, at bottom, Gavyn Bills, and Vania Arevalo. During the attack, the shooter shot a classmate in the head at close range with a shotgun, before killing himself. AP Photo/Brennan Linsley

This Sept. 7, 2013 photo shows Arapahoe High School senior Karl Pierson as he poses for his class picture in Centennial, Colo. Pierson shot fellow student Claire Davis at the school on Friday, Dec. 13, 2013, before killing himself. AP Photo/Mary McGregor

Arapahoe County Sheriff Grayson Robinson holds a picture of Claire Davis the 17-year-old student that was shot during a briefing Saturday, Dec. 14, 2013, at Arapahoe High School in Centennial, Colo. Davis was shot by 18-year-old shooting suspect Karl Halverson Pierson at the school on Friday before he took his own life. AP Photo/Ed Andrieski

A security officer and a sheriff’s deputy walk together, three days after a shooting attack at Arapahoe High School in Centennial, Colo., Monday, Dec. 16, 2013. During the attack, the shooter shot a classmate in the head at close range with a shotgun, before killing himself. AP Photo/Brennan Linsley

Arapahoe High School students hug after leaving items at a makeshift tribute site three days after a shooting attack at the school in Centennial, Colo., Monday, Dec. 16, 2013. They are, left to right, Hannah Eddy, Gavyn Bills, and Vania Arevalo. During the attack, the shooter shot a classmate in the head at close range with a shotgun, before killing himself. AP Photo/Brennan Linsley

Investigators were trying to determine if the occupants of those rooms may have been personally targeted by Pierson.

Robinson has previously said that investigators believed a librarian who headed the school’s speech and debate team was Pierson’s intended target Friday, but he also planned to harm many others. The librarian escaped, but Pierson critically wounded a 17-year-old senior, Claire Davis, whom he encountered soon after entering the school armed with a 12-gauge pump-action shotgun, a machete and three Molotov cocktails. Davis was sitting with a friend near the school library when Pierson shot her in the head point-blank. She remains in a coma.

Pierson ended up killing himself in the library with his sixth and final shot 80 seconds after entering the school, as a school resource officer was closing in.

Robinson also gave more details Tuesday about the amount and type of ammunition Pierson carried – more than 125 rounds of steel-shot, buckshot and slug ammunition.

Also written on Pierson’s arm was the Latin phrase “Alea iacta est,” which translates to “The die has been cast.”

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