Police: Colorado school shooter wrote 'The die is cast' on himself before attack

The student who opened fire in a Colorado school last week had over 100 rounds of ammunition, molotov cocktails and a machete and planned to attack five different classrooms, police said Tuesday.

Karl Pierson also wrote the Latin phrase Alea iacta est -- meaning "The die is cast" -- on his arm when he stormed into Arapahoe High School Friday.

He shot and seriously injured a 17-year-old girl before killing himself in the attack, which triggered hundreds of students and teachers to lock themselves in classrooms, on the eve of the first anniversary of the Sandy Hook massacre.

"The shooter entered the high school armed with a .12 gauge pump action shotgun, and made no effort to conceal the weapon from the view of others," said Arapahoe County Sheriff Grayson Robinson, giving an update of the investigation.

He fired once randomly, then a second shot hit 17-year-old Claire Davis, who has been in a coma and remains in critical condition according to her family. The student fired three more shots, without causing further injuries, Robinson said.

"In addition to the shotgun, the shooter also brought three functional molotov cocktails, a machete in a canvas scabbard and more than 125 rounds of assorted types of shotgun ammunition," he added in a statement.

He used an indelible marker to write the Latin phrase on the inside of his forearm, and also had five different letters and numbers on his arm which detectives correlate to rooms in the school.

Students evacuated from the school Friday reported that Pierson said he was looking for a particular staff member, reportedly a librarian, when he entered the school. That person fled with the help of a janitor.

The sheriff's statement said the teenager "planned to attack at least five areas of the school," adding that investigators are "evaluating if the occupants of those classrooms may also have been targeted for harm by the shooter."

The tragedy occurred a few miles from the sites of last year's Aurora cinema shooting that left 12 people dead during a Batman movie screening, and the 1999 Columbine bloodbath in which 13 were killed as well as the two student gunmen.

The incident came a day ahead of the first anniversary of the Newtown shooting in which Adam Lanza gunned down 20 young children and six adults at Sandy Hook Elementary School.

The Newtown attack briefly reignited the US gun control debate, triggered every time there is a major shooting, but attempts to pass tougher laws have made little headway in Congress.

Watch a report from CNN, as aired on Tuesday, below.