(credit: CBS)

(credit: CBS)

CENTENNIAL, Colo. (CBS4) – A friend of the 18-year-old responsible for the Arapahoe High School shooting says his act of violence came as a surprise to him.

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Alex Espinosa worked at a McDonalds with Karl Pierson for a year in Centennial.

“This is the type of guy that would take a bullet for another,” said Espinosa.

Espinosa called Pierson a great employee who was never argumentative.

“He wasn’t an angry person,” said Espinosa.

Arapahoe County Sheriff Grayson Robinson says that Pierson entered the school armed with a shotgun, a machete and multiple rounds of ammunition.

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He said that 18-year-old Pierson shot one round down a hallway and then another inexplicably at 17-year-old student Claire Davis.

“Shot the female victim point-blank,” said Robinson.

Davis is in critical condition at Littleton Adventist Hospital.

Espinosa says he was shocked after hearing what had happened at the high school.

“I broke down in tears, just very upset and in disbelief. I got in my car and literally pounded the steering wheel a few times,” said Espinosa.

Pierson went on to fire three more rounds and detonate a molotov cocktail in the library before taking his own life.

According to the sherriff the entire shooting event happened in less that one minute and 20 seconds.

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The sheriff says that Pierson bought the shotgun legally on Dec. 6 from a local retail outlet and purchased the ammo sometime a few days ago.