From the BBC page on this story:
He said video footage showed Mr Peterson arriving at the building where the shooting broke out about 90 seconds after the first shots were fired, and that he remained outside for about four minutes. The attack lasted six minutes, Sheriff Israel said.
"I am devastated. Sick to my stomach. He never went in," Sheriff Israel said.
Asked what Mr Peterson should have done, Sheriff Israel said: "Went in, addressed the killer, killed the killer."
Mr Peterson is yet to publicly comment on what happened. Officers are reportedly guarding his home. It is unclear if he will face charges.
The suspect used a semi-automatic AR-15 rifle, police say, and escaped the scene before being captured later.
What was Deputy Peterson's role?
School resource officers are sworn law enforcement officers who are responsible for safety and crime prevention in schools, although their exact roles differ from school to school and authority to authority.
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As suspected, an armed and sworn law enforcement officer who failed to carry out the basic duties he was charged with on a daily basis. Shame on him.