Report: School shooter wanted revenge for teasing

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Colorado School Shooting Leaves Arapahoe High School Student Wounded, Gunman Kills Self
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Report: School shooter wanted revenge for teasing
A makeshift tribute site bears the name of severely wounded student Claire Davis, who was shot by a classmate during school three days earlier in an attack, in front of Arapahoe High School in Centennial, Colo., Monday, Dec. 16, 2013. Davis, age 17, was shot in the head at close range with a shotgun, and remains in a coma. (AP Photo/Brennan Linsley)
CENTENNIAL, CO. - DECEMBER 19: Senior Grace Marlowe pets a dog outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. Grace said, I thought the school would look like it changed, but I realized that just the people inside it had changed, Marlowe said. I wasn't sure if the place that was my home for four years would be different. But its even more of a home now, especially after today. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
Arapahoe High School senior Lily Boettcher, right, and 2013 Arapahoe grad Joy Dafoe hug at a tribute site for severely wounded student Claire Davis, who was shot by a classmate during a school attack six days earlier at Arapahoe High School, in Centennial, Colo., Thursday, Dec. 19, 2013. On Thursday, students were allowed back into school to retrieve their belongings. (AP Photo/Brennan Linsley)
CENTENNIAL, CO. - DECEMBER 14: Hundreds of Arapahoe High School students gathered for a candlelight vigil Saturday night to share their prayers for Claire Davis who was shot inside the school Friday, December 13, 2013. The vigil was held at Arapaho Park in Centennial, not far from the school. Photo By Karl Gehring/The Denver Post via Getty Images
Arapahoe High School senior Lily Boettcher, right, and 2013 Arapahoe grad Joy Dafoe hug at a tribute site for severely wounded student Claire Davis, who was shot by a classmate during a school attack six days earlier at Arapahoe High School, in Centennial, Colo., Thursday Dec. 19, 2013. On Thursday, students were allowed back into school to retrieve their belongings. (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)
CENTENNIAL, CO. - DECEMBER 13: Students and parents wait to be reunited at a Burger King near Arapahoe High School in Centennial, CO December 13, 2013. A student who carried a shotgun into Arapahoe High School and asked where to find a specific teacher opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
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.
Freshman Allie Zadrow, center right, hugs classmate Liz Reinhardt at a church after a shooting at nearby Arapahoe High School. Students from the school were evacuated to the church.
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 students leave their school on a day in which students were allowed back in to school to retrieve their belongings, six days after a shooting attack at Arapahoe High School in Centennial, Colo., Thursday Dec. 19, 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)
Students gather just outside of Arapahoe High School as police respond to reports of a shooting at Arapahoe High School.
Arapahoe High School students hug at a tribute site for severely wounded student Claire Davis, who was shot by a classmate during a school attack six days earlier at Arapahoe High School, in Centennial, Colo., Thursday Dec. 19, 2013. On Thursday, students were allowed back into school to retrieve their belongings. (AP Photo/Brennan Linsley)
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)
Arapahoe High School student body vice president Grace Marlowe looks at a tribute site for severely wounded student Claire Davis, who was shot by a classmate during a school attack six days earlier at Arapahoe High School, in Centennial, Colo., Thursday Dec. 19, 2013. On Thursday, students were allowed back into school to retrieve their belongings. (AP Photo/Brennan Linsley)
Police respond to reports of a shooting at Arapahoe High School.
Sheriffs stand guard over students after they were evacuated to the track and football field at Arapahoe High School. 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.
Parents pick up their daughter at a church where students from nearby Arapahoe High School were evacuated to after the 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, then turned the gun on himself.
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)
Police gather at the Highlands Ranch, Colo., home of the 18-year-old shooting suspect who shot two students at Arapahoe High School on Friday.
CENTENNIAL, CO. - DECEMBER 14: Arapahoe County Sheriff's deputy Evan Driscoll removes tape at an entrance at to Arapahoe High School in Centennial, CO December 14, 2013. Student Karl Pierson carried a shotgun into Arapahoe High School and asked where to find a specific teacher then opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
An Arapahoe High School graduate writes a note at a makeshift tribute site 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)
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)
Surrounded by reporters, Chris Davis, a senior who plays basketball at Arapahoe High School, talks about raising donations for one of the students injured during a shooting at the school in Centennial, Colo., on Saturday, Dec. 14, 2013. (AP Photo/David Zalubowski)
A trooper from the Colorado State Patrol pulls down the safety tape at an entrance to the student parking lot at Arapahoe High School 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) (AP Photo/David Zalubowski)
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)
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
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)
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)
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)
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 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)
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
CENTENNIAL, CO. - DECEMBER 19: Senior Jake Mazer says a prayer outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 19: A woman has a message written on her car outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors will return to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 19: A group of students pray outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 13: Authorities rush to Arapahoe High School in Centennial, CO December 13, 2013. A student who carried a shotgun into Arapahoe High School and asked where to find a specific teacher opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 19: A group of students embrace at the tribute area outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 19: Senior Lily Boettcher, right, is comforted by graduate Joy Dafoe outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. Lily said, 'it was good to be back in the school with everybody. I love my school so much. I couldn't ask for a better community. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 19: Candles burn in the tribute area outside Arapahoe High School in Centennial, CO December 19, 2013. Seniors and Juniors returned to the school for two hour periods Thursday, Sophomores and Freshmen will return on Friday. The victim from Fridays shooting at Arapahoe High School, Claire Davis, 17, remains in critical condition. She was shot on Friday when classmate Karl Pierson opened fire in the school. The gunman died from a self-inflicted gunshot wound. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO - DECEMBER 15, 2013: Students, friends and family arrive at Arapahoe High School for a prayer circle on the track of the school to pray for shooting victim Claire Davis in Centennial, CO on December 15, 2013. Students prayed for the recovery of Davis who was shot during the recent shooting at the high school and remains in critical condition and in a coma. (Photo By Helen H. Richardson/ The Denver Post)
CENTENNIAL, CO - DECEMBER 15, 2013: Students, friends and family arrive at Arapahoe High School for a prayer circle on the track of the school to pray for shooting victim Claire Davis in Centennial, CO on December 15, 2013. Students prayed for the recovery of Davis who was shot during the recent shooting at the high school and remains in critical condition and in a coma. (Photo By Helen H. Richardson/ The Denver Post)
CENTENNIAL, CO. - DECEMBER 14: Arapahoe County Sheriff Grayson Robinson displayed a photo of shooting victim Claire Davis who was shot at Arapahoe High School Friday, December 13, 2013. She is in critical condition. Photo By Karl Gehring/The Denver Post via Getty Images
CENTENNIAL, CO. - DECEMBER 14: Hundreds of Arapahoe High School students gathered for a candlelight vigil Saturday night to share their prayers for Claire Davis who was shot inside the school Friday, December 13, 2013. The vigil was held at Arapaho Park in Centennial, not far from the school. Photo By Karl Gehring/The Denver Post via Getty Images
CENTENNIAL, CO. - DECEMBER 14: People were allowed to pick up cars from the parking lot at Arapahoe High School in Centennial, CO December 14, 2013. A student who carried a shotgun into Arapahoe High School and asked where to find a specific teacher opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 13: A mother comforts her daughter while waiting to be reunited with another outside Arapahoe High School in Centennial, CO December 13, 2013. A student who carried a shotgun into Arapahoe High School and asked where to find a specific teacher opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 14: Arapahoe High School sophomore Avery Griggs, 16, talks about the shooting at Arapahoe High School in Centennial, CO December 14, 2013. Griggs was on the debate team with the gunman as Karl Pierson and and friends with shooting victim Claire Davis. Pierson carried a shotgun into Arapahoe High School and asked where to find a specific teacher then opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - DECEMBER 14: A sign asking for donations hangs at an entrance to Arapahoe High School in Centennial, CO December 14, 2013. Student Karl Pierson carried a shotgun into Arapahoe High School and asked where to find a specific teacher then opened fire on Friday, wounding two fellow students before apparently killing himself, Arapahoe County Sheriff Grayson Robinson said. (Photo By Craig F. Walker / The Denver Post)
CENTENNIAL, CO. - December 13: (center) Jenni Meyers 17 year old senior is comforted by her older sister Mary Myers (left) and mom Julie as they leave Shepherd of the Hills church during a lockdown when a student carried a shotgun into Arapahoe High School and opened fire on Friday, wounding two fellow students before apparently killing himself December 13, 2013 Centennial, CO. (Photo By Joe Amon/The Denver Post via Getty Images)
LITTLETON, CO. DECEMBER 13: Arapahoe High School. A student carried a shotgun into Arapahoe High School and shot two fellow students in Centennial, Colorado December 13, 2013. (Photo by Hyoung Chang/The Denver Post via Getty Images)
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CENTENNIAL, Colo. (AP) - Investigators say the student who killed a classmate before taking his own life at a suburban Denver high school described himself in a diary as "a psychopath with a superiority complex" and indicated he was exacting revenge for being teased in elementary school.

In a report released Friday by the Arapahoe County Sheriff's Office, Karl Pierson, 18, wrote that he planned the Dec. 13 attack at Arapahoe High School to start a conversation about elementary school teasing.

"Words hurt, can mold a sociopath, and will lead someone a decade later to kill," he wrote in a document titled "A diary of a madman."

Police have said Pierson held a grudge against his debate coach and was targeting him when he entered the school with a shotgun, a machete, homemade bombs and 125 rounds of ammunition. Pierson shot and killed 17-year-old classmate Claire Davis before taking his own life in the school library as security officers closed in on him.

The coach escaped unharmed.

Police have said Pierson planned to harm many people. He wrote numbers and letters corresponding to the library and four other classrooms on his forearm before entering the school.

The shootings shocked Littleton Public Schools, one of many across Colorado that bolstered protocols for identifying the severity of threats and fashioning response plans after the 1999 shooting at nearby Columbine High School left 13 people dead. The two gunmen, both Columbine students, then killed themselves.

School disciplinary records showed that in September 2013, Arapahoe High officials deemed Pierson "not a high-level of threat" after he shouted a death threat against the debate coach after his demotion from team captain.

Pierson was allowed to return to class less than a week after the threat. Disciplinary records said Pierson showed no remorse over the incident.

The threat assessment indicated that the teen would see a psychologist once a week to talk about how to manage his anger.

Littleton Public Schools officials have refused to discuss their handling of that incident.

Two days before the shooting, Pierson was sent to the assistant principal's office after pounding on a locked classroom door and yelling, disturbing other classrooms, according to the documents. He was sent home for the day.

Authorities have said Pierson entered the school through a door that should have been locked but was propped open.

Christina Erbacher-Kolk, a school security guard at the time, has said that administrators took no action after she and another guard saw Pierson looking up guns on his computer at school less than two months before the shooting. School officials refused to comment on Erbacher-Kolk's statements.

Second-by-Second Breakdown of the Arapahoe High Shooting

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