Scot Peterson, the police officer assigned to Marjory Stoneman Douglas High School in Parkland, resigned on Thursday, under investigation for failing to enter the building as a gunman opened fire and killed 17 people.

Sheriff Scott Israel said Peterson should have “gone in. Addressed the killer. Killed the killer.”

“What I saw was a deputy arrive … take up a position and he never went in. There are no words. I mean these families lost their children. We lost coaches,” he said. “When we in law enforcement arrive to an active shooter, we go in and address the target and that's what should have been done.”

Video footage showed Peterson did none of that, Israel added, noting that Peterson was armed and in uniform when the shooting began.

The footage shows Peterson outside the building for more than four of the shooting's six minutes. He hid behind a concrete pillar, speaking on his radio, a student said.

Peterson, 54, worked for the Broward County Sheriff's Office since 1985. In 2009, he was chosen as the high school's school resource officer, responsible for safety and crime prevention in the school. There were two prior internal investigations against him.