An armed gunman standing in front of a Florida school and killing 1
US President Donald Trump called him a "coward" for not acting.
Mr. Peterson said he did not know where the shots came from.
The Parkland massacre on Valentine's Day 2018 killed 17 students.
Nikolas Cruz, 19, a former student at the school. was charged with 17 premeditated murder. The police said he admitted the shooting.
- "The day the parkland shooter came to my school"
- One minute after the shootout, silence lasted.
Shortly after, the authorities released footage of Mr. Peterson waiting outside the school when the shootings took place.
Following a Florida Department of Law Enforcement (FDLE) investigation, Mr. Peterson was arrested on Tuesday in seven cases of child neglect, three cases of culpable negligence, and one case of injury.
The investigation found that Mr. Peterson "did absolutely nothing" to prevent the shootings, FDLE Commissioner Rick Swearingen said in a statement.
"There is no excuse for his complete inactivity and no question that his inactivity cost him life," he added.
Broward County sheriff, Scott Israel, voiced his anger after watching the photographs of Mr. Peterson, the four Minutes before the building was left while the murders were taking place. The shoot-out lasted only six minutes.
"I'm devastated, I'm sick, he never went in," Sheriff Israel said, adding that he should have stepped in and killed the murderer.
President Trump said the officer "has certainly done a poor job" and branded him a coward.
Mr. Peterson claimed he believed the shots came from outside the school.
He told NBC that he "did not understand it correctly," but added, "These are my kids in there, I would never have sat there and had my children slaughtered."