UPDATED 10:00 p.m. ET: Authorities have identified the shooter as 18-year-old Karl Halverson Pierson.

The victim reported to be in critical condition is a 15-year-old girl and it's unclear if Pierson intentionally shot her. Arapahoe County Sheriff Grayson Robinson also "did not elaborate on any possible motive."

UPDATED 5:15 p.m. ET: Authorities will not release the name of the suspected shooter, although the sheriff did confirm that person was a student at the school.

The "gunman asked for the location of a specific teacher, who heard he was being looked for, and left the school 'in an effort to draw the student away from the school.'"

A second student was injured during the incident, although that person was not shot.

One student at the school said he became aware of the incident after hearing "three bangs."

UPDATED 4:20 p.m. ET: According to an Associated Press report, the suspected gunman killed himself.

UPDATED 4:00 p.m. ET: The Denver Post is reporting the suspected shooter is dead.

UPDATED 3:50 p.m. ET: The Associated Press is reporting one student is in critical condition.

Police in Centennial, Colorado say there's an "active shooting situation" at Arapahoe High School.

Arapahoe High School is in a nearby district to Columbine High School, which was the site of an infamous 1999 mass shooting spree.

It's also worth noting that tomorrow will be the one-year anniversary of the tragedy at Sandy Hook Elementary School in Newtown, Connecticut.

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