Authorities have identified 18-year-old Karl Pierson as the student who allegedly opened fire at Arapahoe High School in Centennial, Colo. on Friday afternoon.

At a press conference, Sheriff Grayson Robinson said the suspect entered the school armed with a shotgun and asked for a specific teacher. When that teacher heard that the armed student was asking for him, he left the school immediately, and was uninjured. The suspect then opened fire, leaving one 15-year-old girl in critical condition.

Pierson died of a self-inflicted gunshot wound.

This story has been updated to reflect the number of students injured.

Loading Slideshow...
  • A father picks up his daughter at a church where students from nearby Arapahoe High School were evacuated to after a shooting on the Centennial, Colo., campus Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • School Shooting, Grayson Robinson

    Media cover a briefing by Arapahoe County Sheriff Grayson Robinson Saturday, Dec. 14, 2013, at Arapahoe High School in Centennial, Colo., where 18-year-old shooting suspect Karl Halverson Pierson shot student Claire Davis, 17,on Friday, then turned the gun on himself. AP Photo/Ed Andrieski)

  • School Shooting, Grayson Robinson

    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)

  • Arapahoe High School

    Roses and a sign of support are woven into a cyclone fence around a tennis court at Arapahoe High School in Centennial, Colo., on Saturday, Dec. 14, 2013. The school was the scene of a shooting on Friday that left a student gunman dead and two other students injured. (AP Photo/David Zalubowski)

  • School Shooting, Sharon Adams

    Sharon Adams looks through a 2013 Arapahoe High School yearbook at her home near the school in Centennial, Colo., on Saturday, Dec. 14, 2013. The Adams daughter is a cheerleader at the school and escaped unharmed. Pierson critically wounded one student, before apparently killing himself Friday at Arapahoe High School as police moved in. (AP Photo/Ed Andrieski)

  • School Shooting

    The front door at the Highlands Ranch, Colo., home of the 18-year-old shooting suspect Karl Halverson Pierson is covered with plywood on Saturday, Dec. 14, 2013, after the police searched the home. Pierson critically wounded one student, before apparently killing himself Friday at Arapahoe High School as police moved in. (AP Photo/Ed Andrieski)

  • Arapahoe County Sheriff's Department deputy

    A deputy of the Arapahoe County, Colo., Sheriff's Department walks next to crime scene tape in front of a doorway to Arapahoe High School in Centennial, Colo., on Saturday, Dec. 14, 2013. The school was the scene of a shooting on Friday that left the student gunman dead and two other students injured. (AP Photo/David Zalubowski)

  • Arapahoe High School, Arapahoe Sheriff's deputy

    A deputy from the Arapahoe County, Colo., Sheriff's Department gets in his patrol car parked outside the west entrance to Arapahoe High School, the scene of a shooting on Friday, in Centennial, Colo., early on Saturday, Dec. 14, 2013. Investigators were working to find out what motivated a teenage gunman to enter his suburban Denver high school armed with a shotgun looking for a specific teacher a day earlier. The 18-year-old shooter critically wounded a 15-year-old student and was later found dead in the school, apparently of a self-inflicted gunshot wound. (AP Photo/David Zalubowski)

  • Sean Sweeney

    Sean Sweeney, a runner who lives near Arapahoe High School in Centennial, Colo., pauses to say a prayer for the victims and the gunman of a shooting at the school during his early morning run on Saturday, Dec. 14, 2013. The school was the scene of a shooting on Friday that left the student gunman dead and two other students injured. (AP Photo/David Zalubowski)

  • Chris Davis

    Chris Davis, a senior who plays basketball at Arapahoe High School, talks to reporters as he places a donation box for the victim of the shooting at the school located in Centennial, Colo., on Saturday, Dec. 14, 2013. Investigators were working to find out what motivated a teenage gunman to enter his suburban Denver high school armed with a shotgun looking for a specific teacher a day earlier. The 18-year-old shooter critically wounded a 15-year-old student and was later found dead in the school, apparently of a self-inflicted gunshot wound. (AP Photo/David Zalubowski)

  • Michael Vartuli, Chris Davis

    Michael Vartuli, left, and Chris Davis, both seniors at Arapahoe High School, hang a sign asking for donations for the victim of the shooting at the school in Centennial, Colo., early on Saturday, Dec. 14, 2013. Investigators were working to find out what motivated a teenage gunman to enter his suburban Denver high school armed with a shotgun looking for a specific teacher a day earlier. The 18-year-old shooter critically wounded a 15-year-old student and was later found dead in the school, apparently of a self-inflicted gunshot wound. (AP Photo/David Zalubowski)

  • School Shooting

    Police walk up to search the Highlands Ranch, Colo., home of the 18-year-old shooting suspect Karl Halverson Pierson who shot a student at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, then turned the gun on himself. (AP Photo/Ed Andrieski)

  • School Shooting

    Police used a dog to do an initial search at the Highlands Ranch, Colo., home of the 18-year-old shooting suspect Karl Pierson who shot a student at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, then turned the gun on himself. (AP Photo/Ed Andrieski)

  • School Shooting

    Police gather at the Highlands Ranch, Colo., home of the 18-year-old shooting suspect who shot two students at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. The police are expected to search the house Friday night. (AP Photo/Ed Andrieski)

  • Allie Zadrow, Liz Reinhardt

    Freshman Allie Zadrow, right, is hugged by a friend Liz Reinhardt at a church after a shooting at nearby Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. Students from the school were evacuated to the church. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • A parents picks up her daughter at a church where students from nearby Arapahoe High School were evacuated to after a shooting on the Centennial, Colo., campus Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • School Shooting

    Parents pick up their daughter at a church where students from nearby Arapahoe High School were evacuated to after a shooting on the Centennial, Colo., campus Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • Allie Zadrow, Liz Reinhardt

    Freshman Allie Zadrow, right, is hugged by a friend Liz Reinhardt at a church after a shooting at nearby Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. Students from the school were evacuated to the church. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • Courtney Leypoldt

    Courtney Leypoldt, left, is hugged by a family member as she is picked up at a church after a shooting at nearby Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. Students from the school were evacuated to the church. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • School Shooting

    A student stares out a bus window as it arrives at a church to be reunited with family after students from nearby Arapahoe High School were evacuated their after a shooting at the school in Centennial, Colo., Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • A woman screams as she arrives at a church where students from nearby Arapahoe High School were evacuated to after a shooting on the Centennial, Colo., campus Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • Jenni Meyers, Mary Meyers, Julie Meyers

    Senior Jenni Meyers, center, is hugged by her sister Mary as they leave a church with their mother Julie after they were reunited after a shooting at nearby Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said the shooter shot two others at the school, before apparently killing himself.(AP Photo/Brennan Linsley)

  • School Shooting

    Students comfort each other outside of Arapahoe High School after a shooting on the campus in Centennial, Colo., on Friday, Dec. 13, 2013. Arapahoe County Sheriff Grayson Robinson said Friday that the shooter, who died, was a student at the high school. He said another student was wounded when he confronted the armed student and was shot. (AP Photo/Ed Andrieski)

  • School Shooting

    Sheriffs deputies stand guard over students after they were evacuated to the track and football field at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, where a student shot at least one other student at a Colorado high school Friday before he apparently killed himself, authorities said. The shooter entered Arapahoe High School in a Denver suburb armed with a shotgun and looking for a teacher he identified by name, said Arapahoe County Sheriff Grayson Robinson. (AP Photo/Ed Andrieski)

  • School Shooting

    Sheriffs deputies stand guard over students after they were evacuated to the track and football field at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, where a student shot at least one other student at a Colorado high school Friday before he apparently killed himself, authorities said. The shooter entered Arapahoe High School in a Denver suburb armed with a shotgun and looking for a teacher he identified by name, said Arapahoe County Sheriff Grayson Robinson. (AP Photo/Ed Andrieski)

  • School Shooting

    A sheriff deputy talks on his radio at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, where a student shot at least one other student at a Colorado high school Friday before he apparently killed himself, authorities said. The shooter entered Arapahoe High School in a Denver suburb armed with a shotgun and looking for a teacher he identified by name, said Arapahoe County Sheriff Grayson Robinson. (AP Photo/Ed Andrieski)

  • School Shooting

    Students comfort each other at Arapahoe High School in Centennial, Colo., on Friday, Dec. 13, 2013, where a student shot at least one other student at a Colorado high school Friday before he apparently killed himself, authorities said. The shooter entered Arapahoe High School in a Denver suburb armed with a shotgun and looking for a teacher he identified by name, said Arapahoe County Sheriff Grayson Robinson. (AP Photo/Ed Andrieski)

  • In this still image taken from video provided by Fox 31 Denver, students gather just outside of Arapahoe High School as police respond to reports of a shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013. Colorado division of emergency management spokeswoman Micki Trost said her director went to the school and their weren't any more immediate details. (AP Photo/KDVR) MANDATORY CREDIT

  • In this still image taken from video provided by Fox 31 Denver, police respond to reports of a shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013. Colorado division of emergency management spokeswoman Micki Trost said her director went to the school and their weren't any more immediate details. (AP Photo/KDVR) MANDATORY CREDIT

  • In this still image taken from video provided by Fox 31 Denver, students gather just outside of Arapahoe High School as police respond to reports of a shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013. Colorado division of emergency management spokeswoman Micki Trost said her director went to the school and their weren't any more immediate details. (AP Photo/KDVR) MANDATORY CREDIT

  • In this still image taken from video provided by Fox 31 Denver, police respond to reports of a shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013. Colorado division of emergency management spokeswoman Micki Trost said her director went to the school and their weren't any more immediate details. (AP Photo/KDVR) MANDATORY CREDIT

  • Police respond to the shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • The FBI is seen responding to a shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Police respond to the shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Students were escorted out Arapahoe High School in Centennial, Colo. with their hands up after a shooting broke out on Friday, Dec. 13, 2013.

  • Police respond to the shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Arapahoe County Sheriff Grayson Robinson speaks during a media briefing about the shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Colorado Gov. John Hickenlooper speaks at a media briefing about the shooting at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Colorado Gov. John Hickenlooper is seen shortly after a press conference at Arapahoe High School in Centennial, Colo. Friday, Dec. 13, 2013.

  • Arthur Blessitt of Littleton who is <a href="http://www.guinnessworldrecords.com/world-records/1/longest-ongoing-pilgrimage" target="_blank">listed in the Guinness World Records</a> for the world's longest walk carrying a wooden cross around the world was nearby after the the shooting at Arapahoe High School in Centennial, Colo. on Friday, Dec. 13, 2013.

  • Buses carrying students from Littleton Public Schools leave after a shooting occurred at Arapahoe High School in Centennial, Colo. on Friday, Dec. 13, 2013.

  • CO SCHOOL SHOOTING 2

    UPDATES WITH DETAILS OF THE EVENTS: Map locates Arapahoe High School shooting. ; 1c x 3 inches; 46.5 mm x 76 mm;